Column

Answer:

Hi Jan,

The absolute best is to bury the tree directly into the ground. The first few years, I would probably protect the ground where the trunk stands, because it is a big tree. You can for example use a thin plante of polystyrene for that. If there is hard frost, wrap the tree in some fiber cloth. If you plant the olive tree in a pot, it is particularly sensitive and it is important to insulate the pot thoroughly. It is especially frost at the root that can kill an olive tree.

Best wishes,

Lars Lund

Answer:

Hi Sten,

Thanks for your question.

It is not the bubble wrap as such that increases the heat, but the glass. Only a little sunshine is needed these days to warm up the greenhouse - that's right. When the greenhouse is warm leave the door open and if you have windows, you can open them as well. That should be sufficient to keep the temperature at the right level. Most people remove the bubble wrap around April 1st. Should there be frost afterwards, you can wrap delicate plants and then take the wrapping off again when the frost is over.

Best wishes,

Lars Lund

Answer: 

Hi Susanne,

There are several herbs you can cultivate in the greenhouse in winter. However, it is important to use herbs, which are accustomed to the climate, and which have grown outside all summer. That means, using herbs bought in the supermarket, which were cultivated in an industrial greenhouse, are not an option. The classical herbs can be divided into two main groups:

Tolerate frost and can overwinter:

Some herbs are hardy and perennial plants or low shrubs, depending on their growth. Characteristic for those herbs is that they grow again year after year. Herbs in this group are for example: chervil, mint, oregano, sage, parsley, thyme, chives, chamomile, lavender, and lemon balm. Rosemary is also perennial, but not always hardy. All those herbs can be cultivated in the greenhouse in winter.

Herbs requiring warm temperatures:

Herbs in this group require warm temperatures to thrive. Some herbs need the warmth because they originate from warmer countries. In this group are all types of basil and coriander. They need at least 15-20 degrees Celsius for the seeds to germinate and for the plants to grow harmoniously. Both basil and coriander are very sensitive and don’t thrive outside in could summers. Basil can be sown in the greenhouse in the end of May, when the temperatures begin to rise. Those herbs cannot be cultivated in the greenhouse in winter.

Best wishes

Christine Wiemann

Answer: 

Dear Kirsten,
If the problem is the capacity of the rainwater butts and that the butts are overfloating, I would use a piece from a garden hose to divert the water.

Attach the garden hose piece at the tip (see picture) and slowly turn on the tap to divert the water.

Best wishes Klaus Lillsø

Answer:

Dear Susanne,

I have written a couple of articles about this topic in the past. If you write “storm” in the search box, you find the articles. You also find the links below:

• Avoid storm damages
• The great storm investigation
• Safeguard the greenhouse before the storm
• Shards of glass

These tips are of course no guarantee, and even with careful preparations, damages can happen. It can be a good idea to check what your insurance covers, just in case, or to consider getting an insurance, if you don’t have one to begin with.

Best wishes

Lars Lund

Answer: 

Dear Carsten,
You don’t have to be concerned. Sometimes my vine looks the same, especially the older leaves. There might as well be a natural explanation since they start winter dormancy early in which the chlorophyll is drawn out of the leaves. Often this happens when the plant is stressed during periods of drought. Another reason could be lack of calcium or magnesium – especially the last one. If magnesium is the issue, you can dissolve 100g of Epsom salt in 10 litres of water. Spray the mixture on your vine after flowering. This is normally mid-June. The soil you cultivate your vine in should have a pH between 6 and 7. And rather 6 than 7 if the plant lacks magnesium. Don’t use too much nitrogen when fertilizing. Only use a small dose just before the flowering in May and some again in July. If they get too much, it will grow a lot of leaves, the grapes will become worse and the vine will get damaged during winter. But you shouldn’t be worried. Just pay attention during periods of drought. Read more about the possible causes here.

Best wishes Lars Lund

Answer: 

Dear Bent,
Some tomato sorts produce a lot of large clusters with flowers. It is usually sorts with small tomatoes. The plant will regulate this depending on how many tomatoes it can develop and produce. If the plant has too many female flowers, it will stop the development of the fruit and the female flower dies. Remember to only use tap water and fertilizer when cultivating in capillary boxes. It is also important to remove the leaves from the roots and up to the first cluster which is ripening in July.

Best wishes Christine Wiemann

Answer: 

Dear Lene,
There are multiple reasons for leaf edges to brown. In some cases the plant is getting too little or too much fertilizer. In other cases it is too little water. But since you are using capillary boxes and I believe you are correctly fertilizing, I don’t think irrigation or fertilizer are the problem. And yet: if it is very hot, you don’t need to fertilize or at least only fertilize every other week. If the leaves get pale, it is a sign of too little fertilizer otherwise more fertilizer is not needed. The plant uses a lot of water to cool itself down when it is hot, therefore, overfertilizing can be harmful. Another reason is that the greenhouse has been too warm and that the plants have not been protected from the light. The top is definitely attacked by grey mould (due to high humidity), but I cannot say whether the mould is the cause of the top withering (it could also be the heat) or if the mould appeared after. In general, avoid overfertilization and don’t forget to shade your plants and ventilate.

Best wishes
Lars Lund

Answer: 

Dear Tove,
Whiteflies are problematic in the greenhouse. Whiteflies are related to lice and they have sucking mouth parts which is why they are typically found on the undersides of leaves and sucking the sap from the cells of the plant. They are easy to see since they are white. Whiteflies excrete a sugary sticky liquid called honeydew. The honeydew appears on the leaves as a glistening layer. The honeydew is the actual problem rather than the pests. The dew makes it more likely for the plant to get attacked by fungus diseases such as sooty mould which will lie as a brown or black layer of powder on the leaves. In my garden it happens to my cabbage when I winter cultivate, and in the greenhouse it is the tomato plants. The solution is to keep the greenhouse clean by washing the greenhouse twice a year.  

Best wishes
Christine Wiemann

Answer: 

Dear Villy,
Hopefully, you have bought Laurus Nobilis and not the cherry laurel (Prunus laurocerasus) because the cherry laurel is poisonous. Usually, the laurels are not eaten, not even the Laurus Nobilis. Instead, the oil is extracted from the leaves and the leaves are then disposed. But if you like a dry bay laurel, that is fine too. Bay laurel is not resistant to frost, so it may depend on when you bought it. If it was here in the spring and the leaves are already brown, then I would return it and get a new one. In case it has not been protected from the frost, it is likely it has been damaged by the cold. Maybe the plant has not gotten enough water or gotten too much. Theoretically, it could also have been attacked by a fungus disease. No matter what you can still dry the leaves, and if the plant is dead due to overwatering (during winter they need almost no water) then it means that the leaves have been drying anyway. On the other hand, there are not much aroma in the ones that are dry. The plant must be placed in the greenhouse or somewhere sunny and sheltered.  

Best wishes
Lars Lund

Answer:

Dear Christina,

Yes, it will be 3 meters, and that is the length that most seedless vines get. Another popular variety, which is almost seedless is Himrod. They get up to 10 meters. I have a blue Schuyler in my greenhouse. It can easily become 10 meters and has small seeds. Vanessa is almost seedless with red grapes and it can also get up to 10 meters. When you transplant the vine directly in the ground, remove a stone and irrigate now and then for two years. Thereafter, it can get water by itself. In my blog “Get a southern roof in your greenhouse” I show how to hang up vines.

Best wishes
Lars Lund

Answer: 

Dear Tove,

Thank you for the question. Matina is an older sort, that grows leaves similar to the leaves on a potato plant. Which makes sense since tomatoes and potatoes are part of the same botanical family. The colour may differ from newer sorts. Using potting soil is fine but remember that potting soil often has an expiration date.

Add fertiliser to the irrigation water a few times a week and follow the instructions on the packaging. Also, avoid using rainwater and instead use tap water. Your plants should be placed somewhere with a lot of light and at a temperature at about 20 degrees. If the plants are getting long and thin, it is a sign of that they are not getting enough sunlight.

Best wishes
Christine Wiemann 

Answer: 

Dear Inger,

If it is small and curved trails it could be leaf miners. They usually walk on the leaves, and it is often on tomato leaves, but they also appear on cucumbers. Fungus diseases may also leave trails, but these are usually yellow or brown with small indentations. Another fugus named Phytophtora capsici. can also leave some white stains. Plant Villages, an organisation helping smallholder farmers grow more food, has made an image gallery of cucumber diseases and pests. Here you may find your answer plantvillage.psu.edu. The photo above is from Nyttedyr.dk and shows trails from the leaf miner. You can trap the insects with yellow sticky traps. Put up the traps when or after you transplant your plants.

Best wishes
Lars Lund 

Answer: 

Dear Mrs. Friis,

You are not alone with this problem. There are multiple options. It is most likely some kind of moth larvae. They lay their eggs on the leaves and when it hatches the larva eats the peppers. Alternatively, it could also be slugs. To be more certain an image of the damages or the pest would be helpful.

I have discussed the matter with my colleague Magnus Gammelgaard, a garden expert from plantedoktoren.dk. He does not think it is earwigs that have fed on the peppers, but they do sometimes crawl inside the fruits. Slugs are also a good bet or the bright-light brown-eye moth (Lacanobia oleracea). This moth gets large larvae, but even large larvae were once small. They love peppers (Capsicum), Magnus says. Another option is the angle shades moth, who also likes peppers. This moth flies inside to lay its eggs on the leaves in summer.

It is difficult to give advice without any images, but I will try nonetheless. You can make a beer trap to get rid of slugs and snails. The slugs will be attracted to the beer and fall in and drown.

Magnus suggests to put up netting in front of the door and the windows in the greenhouse, so the moths cannot get inside. But this will also make it more difficult to ventilate. Otherwise, you can remove the larvae by hand at night since they are hiding during the day.

A last suggestion is to sprinkle cayenne pepper on the leaves of the pepper plant. This helps to keep the pests away. You can also use a mixture of garlic and cayenne pepper to spray on the plant. It is easy to make, you only need six cloves of garlic, 1 tablespoon of cayenne pepper, 1 tablespoon of onion juice and 1 teaspoon of liquid soap in 4 L of hot water. Put it all in a food processor until the garlic cloves turn to liquid.

Best wishes
Lars Lund

Answer: 

Dear Bjarne,

Yes, it is scale insects. With that many scales on the plant, it will need multiple treatments with neem oil. In fact, I would also use alcohol and try to brush the insects away. Place a paper over the pot, so the insects do not fall in the pot while brushing them away. You must be thorough and go through every leaf and stem. Then you can use the insect soap or the neem oil mixed with water and repeat this process once a week for at least three weeks.

Best wishes
Lars Lund 

Answer: 

Dear Grethe,

You can start to find out how they have gotten inside a closed capillary box. They must have crawled up under it or from the side. Ants do not like a humid environment, so keep it moist for a while. A more harsh way is to use boiling water. They must be right under some of the tiles in the greenhouse. There are a few options. You can buy organic pesticides that seal their tunnels. You can also use coconut oil, which will kill the ants. Another method is to use a mixture of icing sugar and potato starch (half and half). In general, ants are useful animals, but they also help aphids, which is an insect we do not want. A tip to keep them away for a while is to use coffee grounds.

Best wishes
Lars Lund 

Answer: 

Dear Tove,

It looks like spider mites, which are common on citrus plants. You can get predatory mites that eat them, but it might be a bit expensive way to get rid of spider mites. First, you can try with insect soap. Otherwise, you can use neem oil which many have had success with. On the Greenhouse Forum you can find a video that shows you how to use it.

Best wishes
Lars Lund 

Answer: 

Dear Else,

My first thought was that it is slugs. They can make a foam that looks like that, but then I talked to a previous producer of hyacinths. According to him, it is a fungal disease and he recommends that you get rid of them immediately. You will never get them to bloom and the disease can be transmitted to other plants. I will advise you to take the plants to the shop where you bought them, to get some new ones and to ask the shop to make their producer aware of the problem.

Best wishes
Lars Lund 

Answer: 

Hi Ole,
Yes, it is possible. But you may need to control the humidity, the amount of light and the temperature – at least if it is done on a larger scale and professionally. Many people are also growing tomatoes with artificial light as a hobby. I, myself am cultivating chillis that I sowed this September. But they are growing very slowly. For further reading I recommend my article about artificial light which you can find here.

Best wishes
Lars Lund 

Answer: 

Hi Jens,
The fewer leaves there are after the grapes the more sour the grapes may be. In the greenhouse there should be two leaves after a cluster but four are better. But sometimes there is not enough room for four. The sunlight is also important. The more sunlight that falls on the grapes the better. There is nothing more to do than wait until they are fully ripe.  

 Best wishes
Lars Lund 

Answer:

Dear Vivi,
It is mealy bugs in your sunroom and they are really annoying and not easy to get rid of when they are on the grapes. You can buy insecticide, but then the grapes won’t be edible for the rest of the year. Alternatively, you can buy Cryptolaemus. Dishwashing soap, a bit of alcohol and 1 litre of water may also be used, but I do know they are tough so you may have to repeat the process.

Best wishes
Lars Lund 

Answer:

Dear Tove,

In the picture, it looks like you manage the gardening very well. And what a beautiful greenhouse your husband has built.
Tomato leaves tend to curl. It does not affect the yield. It is the accumulation of starch that can occur if the temperature is either too low or too high. In this case, probably too high. The different colours of the leaves could be due to tobacco mosaic virus that can be transmitted from smokers. However, there are no typical signs that this is the case. Other viruses may give the same picture. I think your problems have to be coupled with the slightly too high temperature, but it is no disaster. It is very common for tomatoes to get various small diseases on the leaves in hobby greenhouses. The most important thing is that you ventilate well and leave both doors and windows open around the clock. The soil must not be saturated in water, as it very much likes to dry out between irrigations. In fact, there are also some who never irrigate their tomatoes, even if they are in a greenhouse in a bed. (You can find a video about it here in the GreenhouseForum). So, you must avoid waterlogging and air out.

Best wishes
Lars Lund

Answer:

Dear Lars, it clearly looks like drought damages. These can often be associated with a lack of nitrogen, so I would partly recommend that you give the vine some fertilizer, while you irrigate thoroughly. Start by irrigating the ground well. Then let it soak and then irrigate with liquid fertilizer the next day.

Best wishes
Lars Lund

Answer:

It is difficult to give a general answer about that, as several factors may come into play. The cucumber nurseries have automatic control, so the cucumbers get exactly the water and nutrition they need, but even in such cases, you can experience soft cucumbers also among those purchased. This is very much about how both you and the store have stored the cucumbers. Cucumbers are extremely sensitive to cold and if they are in a temperature below 7 degrees, perhaps in a refrigerator that is too cold, then they become soft. If the greengrocer has had his cucumbers in stands on the street in frost, the cucumbers also go bad.
The best storage is around 10 degrees or on the kitchen table. They last even better when wrapped in film and therefore you also see many cucumbers you buy wrapped in film.
Cucumbers are also very sensitive to ethylene which comes from apples and tomatoes, so they should not be stored together.
Asparagus can also quickly lose their crispness, but you can make them last longer if you cut 0.4 inches off the end of each plant you have harvested. Then place them in a glass of cold water. If necessary, cover the asparagus in the glass with a plastic bag, but so that your asparagus does not touch the bag. Finally, put them in the fridge. There are also several chefs who have good experiences with repeating this process, if the asparagus becomes soft (which they do quite quickly), so cut a piece of the bottom again, put them in bundles and in a glass of water. The method also works outside the refrigerator. You can also wrap them in a damp cloth and put them in the refrigerator.
Some refrigerators have a drawer called BioFresh that makes it possible to create optimal storage conditions for vegetables (not cucumbers and tomatoes). A BioFresh drawer has an adequate humidity level at just 0.

Best wishes
Lars Lund

Answer:

Hi Dan,
Nothing is stopping you from using the solution you suggest yourself, but I think it comes as a surprise to many who for several years have used drip irrigation with the same amount of fertilizer for both tomatoes and cucumbers. I have searched on the internet whether cucumbers should have more fertilizer than tomatoes to find out if it is true, how much in that case, and if there is any documentation. I found a single statement where a debater wrote that she has read somewhere that cucumbers should have more fertilizer than tomatoes, but she cannot remember where she has read it and there is, therefore, no documentation of the statement.
On the other hand, cucumbers need a lot more water than tomatoes need, but even if we over irrigate tomatoes, they are not harmed. It's just not necessary.
Jørgen Jørgensen from Denmark, for example, grows tomatoes in his greenhouse completely without irrigating them.
Back to fertilizer. Although I have never made a difference between tomatoes and cucumbers in terms of fertilizing, there may be something I do not know and my cucumbers have not been aware of either, because they have not protested. After I had searched through the internet, I contacted two Danish nurseries that grow both cucumbers and tomatoes, and both agree. If there is a difference, then it is so small that it does not matter, they say. One nursery clearly says no, and the other says that if there is a difference, it is so small that it has no real significance.

Best wishes
Lars Lund

Answer:

Hi Janne,

At certain times of the year, there are many flies in the house and not least in the greenhouse, but they disappear quite quickly again - in my experience. Not least if you live in the country or near a horse farm, there are many flies. You can of course buy a fly spray, but it's poison, so it's not something we recommend. You can rather use the old-fashioned fly glue traps, even though it's a kind of animal cruelty. There are also sheet traps with glue, but you have to decide that yourself. Otherwise, I can recommend basil, as most insects stay away from its smell.
I would perhaps prefer the advice of using vodka, which the flies do not like either. If vodka is hung up in small plastic bags, the bags of vodka also make some gleams when the sun hits the bags, which also deter flies. Other remedies are lavender oil and cloves on oranges. That will also bring out the Christmas mood. A more exotic method is quails. If you want quails in the greenhouse, they catch flies and of course the best solution: fill the greenhouse with flesh-eating plants. Finally, there are several lure traps and electric insect killers on the market.

Best wishes
Lars Lund

Answer:

Hi Isabelle, Thanks for your question regarding the Vanlet.

The amount of water that can be regulated is from about 10L to 150L per 24 hours via the red control tap. As you say that the water level is at the top of the red measuring glass and it takes approximately 30 minutes to fill up the tub, it sounds like the right amount of water is supplied to the drip sticks. If it is assumed that it takes 30 minutes to fill, this is done approx. 48 times in one day. From here we have to subtract the 10 minutes that it takes to be emptied. If we do this, You use approximately 130L a day. There are a number of factors that can make the inflow vary from customer to customer, such as surface tension in the water, pressure in the water and shore (the hardness) in the neoprene gasket in the measuring glass.

When you say you turn it up further and water flows from here, I would think it is because it is already at the maximum inflow to the tub. The red measuring glass itself will be emptied when the water pressure is switched off. Why the tub itself is emptied I cannot say, as it is usually only emptied when it has reached the level for emptying.

I hope the answer can eliminate your challenges/wondering.

Best wishes
Klaus Bisgaard Lillesøe
Quality manager, Juliana Greenhouses

Answer:

Hi Ditte, Thanks for your question.
I really had no doubt that it is mildew, but since it typically occurs in the summer, I just had to investigate it further, and it is now clear to me that it is mildew. It would be great to know the age of your vine and the sort. Some sorts tend to get mildew often, while others are almost resistant. If your vine is older, I would wait and see, but everything you do is correct. Ventilate well, make sure that the plant does not lack water, remove the diseased leaves immediately, and yes, other plants can be infected in dry weather and mildew thrive in the humid air.

Once the plants are infected with mildew, you cannot do anything else but remove the sick. There is no remedy for mildew once it has infected the plants. There are various fungicides on the market that need to be sprayed on before the mildew attacks, but that can be a little difficult to know. Maybe it can have an effect on what is not infected. If your vine is a younger one, replace it. Schuyler, Himrod and Vanessa are probably the most resistant sorts to the disease.

Best wishes
Lars Lund

Answer:

Hi Joan,
Potted plants are always much more exposed to frost. The soil can easily freeze in the bottom and then the plants usually die, but if the pot has been insulated or not exposed to a long period with frost, branches can also freeze back. Large branches too.

This year, there had been frost in longer periods, that is several days straight and my fig is frozen quite a lot here and there. My shoots are bare too. However, it is completely normal after a long cold period and there has not really been any heat to start it all again. However, I think there is definitely life in it, so just have a little patience and cut off what does not shoot, when something else shoots but not before. You can check with a nail gently scratching in the bark of the main stem. If it is green, like mine, then there is life and hope. I believe it will catch up quickly.

Best wishes
Lars Lund

Answer:

Hi Elsa,
You can do that if you want large uniform grapes. You can prune in two ways. If you have a lot of grapes, cut along the stem (midribs) so that half of the grapes are cut off. The grapes that are left will then develop and spread out in the direction where there is most space. The more common method for us hobbyists is to use a pair of scissors that are long and pointed and thin out the entire vine so that up to half of the grapes are cut away. Some grape varieties need thinning more than others. Avoid putting too many fingerprints on the grapes during thinning, as they will lose the fine misty surface.

Best wishes
Lars Lund

Answer: 

Hi Bente, 
Most citrus plants that have edible fruits do not tolerate frost. If the stem is green under the bark, you may be lucky that they have survived anyway. You must then have great patience and wait until June to see what happens. I would recommend waiting to cut back what you think is dead, but feel free to remove all dead leaves.

Best wishes 
Lars Lund 

Answer:

Hi Finn,
Thank you for the creative question. Yes, you can use the leaves as a ground cover. You can also use cut grass which will both hold moisture and fertilize, although the process is slow.

Best wishes
Lars Lund

Answer:

Dear Benita,
If the greenhouse is not heated, as you do in homes that are insulated, it does not make sense to insulate the floor, as you also get heat from the ground. Almost all the cold in a greenhouse comes from the glass, or we can say from the outer environment, and it, therefore, makes sense to use bubble wrap in the winter. You are also asking about the base, and the answer is yes. Although, there are many discussions about whether it pays off and whether it should be on the inside or outside of the base. I recommend insulating from the outside. There is no risk of polystyrene emitting anything to the ground.

Best wishes
Lars Lund

Answer:

Hi Elsa,
I have a good old vine myself, that is now in a larger greenhouse, but I did not move it. It just got another location, because the greenhouse was bigger. I pruned it a bit just to get more space working around it. I did it in the winter when I knew I would have a new house up the following spring and knew the location. There are several opinions on whether you can move a vine or not, and there are also different experiences. Some people think that you cannot move plants that are more than 5 years old, and others have such good experiences with moving even 15-year-old plants. Some say plants must be moved in the winter or at the latest before spring (December-April), but first, they must be pruned so it is almost just the stem that is left. You dig up the plant and make sure to get as many roots as possible, in practice only a very small part of the root can be dug up. They must be transplanted immediately so the roots do not dry out. The dormant buds will shoot the next summer, but the shoots do not become very large the first year. You must let the plant take care of itself the first year. In the 2^nd year, you can begin to shape the plant with new horizontal shoots, and after 3-4 years, you can yield grapes again. Typically, I think it seems that those who have tried it have not had problems, while those who have not, do not think it is possible.

Best wishes
Lars Lund

Answer:

Hi Mogens. Thank you for your very good question.

Growbags are often associated with growing in capillary boxes, ie polystyrene boxes, where you only need to irrigate once a week, but of course, you can also just lay the bag on the ground and then irrigate with a watering can every day. Most growbags have a fertilizer that lasts the first 14 days. You must read on the back of the bag, where it says whether fertilizer has been added or not. The cheapest ones are often without any fertilizer, which is the reason for the price. Growbags with animal manure are more expensive than the ones with NPK fertilizer, also called artificial fertilizer. After 14 days, you should fertilize with a fertilizer of your choice. However, if you use capillary boxes, it must be a liquid fertilizer. Fertilizer can be composed in different ways, you just need to read on the back of the packaging what is recommended. You can also choose between organic and ordinary fertilizers. If it is not organic, it is a common fertilizer.

Tomatoes can get too much sun. If they do, they get sunscald. That is, the cells are destroyed so that they do not mature in the "stem", ie where they get sun. Bigger is the problem of too much heat, so here you have to remember all summer to ventilate well. Just leave the door open around the clock when the tomatoes are ripening.
Cucumbers are the most heat demanding compared to tomatoes. Therefore, you place them the furthest away from the doorway.
Peppers also do not require much heat and can, therefore, like many tomato sorts, be grown outdoors, but chilli, (which is also a pepper) should get as much heat as possible. Tomatoes need light, but preferably not direct sun, so leave the leaves on the plant unless they are sick or withered. Cucumbers want lots of light, so find the right location.

We all started somewhere, and it is somehow very satisfying to get wiser even if one fails a few times. There are so many factors that can come into play that you are not in control of anyway. But a really good tip: You mustn’t transplant your plants too soon. Tomatoes and cucumbers as well as peppers are already being sold in nurseries and people are being lured to transplant them far too soon. When they fail, you think it's your fault, but the mistake is that they are sold too early. Tomatoes should be transplanted no earlier than mid-May and cucumbers on June 1st.

Best wishes
Lars Lund

Answer:

Dear Michael,
I have previously had my good friend Steen Rasmussen from the Danish architect greenhouse company Drivadan, calculate it.

I most common greenhouses, without any kind of insulation (polycarbonate, curtains, aluminium profiles etc.), you need 200-250 Kcal / m2 at -12 / +18 degrees (we set the u-value of the glass to 5.8).
The number will then be smaller in terms of insulation and "only" frost-free, and you can also calculate that purely theoretically, if you have the black belt in that kind of stuff, as Steen has.
In Steen's experience, you need 100-150 kcal / m2 if it is to be kept frost-free, even on the (maybe few) cold days.
If you have a greenhouse of 25 m2 and would like it to be frost-free even on cold days, a guess is 100 kcal x 25 = 2500/860 = about 3kW, but that is without technical documentation.

As soon as you turn off the fireplace the heat will quickly disappear though. On Instagram, you can follow @glimtbybloch, who besides having a small portable wood stove that I have installed, has an electric oven and a gas fireplace. Gas has the disadvantage that it emits a lot of water, so you need to air out. I know that she mainly uses the gas fireplace in front of the greenhouse and only occasionally inside the house.

Best wishes 
Lars Lund

Answer:

Dear Sten,
There are actually many different reasons, ranging from being natural on the Chinese sorts to that it could be viruses, lack of nutrients (especially manganese) or too small pots. There is a really good website that tells you all about chillies, including how to grow them. It is made by a passionate chilli grower.
The website will teach you more about chillies.

Best wishes
Lars Lund

Answer:

Dear Ulla, 
Well, look at that. I have a wood stove in my Oase, which I also use in the summer. Let me start with your citrus and heat. Citrus definitely benefit from being outside in the summer. The term orangery stems from heated greenhouses that are used in the winter, but in the summer the citrus plants will always get put outside. About the shade: Juliana makes roller shading blinds with suction cups you can place almost wherever you want. You need those and shade nets. In addition, you can with advantage leave the door completely open. Another solution is to put up a wire in the ceiling, at the height where the glass meets the roof. Here vine can crawl and provide shadow. I've done that in part of my Oase. You can also use other creeper plants. The wires are almost invisible, and you can also hang white curtains on them.

Maybe you can find inspiration in some of these links from the GreenhouseForum:
Air out with the right window opener
How to prune your vine easily

Best wishes
Lars Lund 

Answer:

Dear Erling,

Figs tend to get huge in the greenhouse so most end up taking them out and putting them up against a south wall.

Figs grown in the northern countries have been in demand at Gourmet restaurants. They taste better than fresh, bought figs from abroad. The explanation is that exported figs are picked and sold long before they are actually ripe, which affects the taste. If the figs can otherwise mature, they are in other words a delicacy if grown in northern countries. And they can ripe. You just have to choose the correct sort. You cannot just take a plant home from the south and get figs out of it.
If you grow them outdoors, figs must also be in the poorest soil of the garden.

Although, the greenhouse offers the opportunity to grow sorts that you normally would not succeed with outside. Those are Petrovaca Gigante, Hardy Chicago and White Marseille, Hirta, Vallecalda and Ronde de Bordeaux.

Apricot can also be difficult to grow, even in a greenhouse, as they are very heat demanding, but nothing is impossible. Harcot and Hargrand are both healthy sorts. In Norway Kuresia prunos Amenica is a very popular sort.

Best wishes
Lars Lund

Answer:

Dear Elsebeth,

You are writing cucumber downy mildew, pseudoperonospora cubensis, so I assume that is the case. Melons can get up to 11 different viruses and fungal infections, and some of them may well resemble each other. In the case of cucumber downy mildew, the leaves get pale yellow spots, which can also look like spider mites. The spots quickly become clearer and more angular, and resemble mosaic delimited by the leaf nerves. The leaves wither and new spores infect the other plants. In humid weather, it may be filled with grey-black spores on the back of the leaf. The mosaic pattern on melon leaves can also be caused by a virus. For us at home, there is not much else to do but check the plant regularly and remove the disease when it comes. You cannot do anything to kill viruses like that, but fungal diseases can be alleviated by ventilating well throughout the summer. You can easily leave windows and doors open once the plants are in growth. Washing and cleaning the greenhouse as you do is always good against all sorts of diseases.

Best wishes
Lars Lund

Answer: 

Dear Ellinor,
What a good question for the column, thank you for that.

Horse manure is worth its weight in gold for us garden owners, as it is useful in many ways, both as a soil improvement, nutrient enrichment and for hotbeds. Horse manure mixed with sawdust can be used for heating beds, but as you yourself suggest, there are a few disadvantages of sawdust rather than straw. The sawdust takes a lot longer to compost, so the decomposition process will not go quite as fast as for straw. This will therefore result in a smaller heat exchange from the composting. In order for the heat release from the composting to really have a noticeable effect, you must make a good thick layer of approximately 20 inches.
I should also mention that the decomposition of fresh sawdust and wood chips will cost the soil nourishment before it is released again. Of course, it is also worth investigating whether the sawdust originates from pressure-impregnated wood or glulam, as this treatment protects the wood from decomposing.
If it was me, I would look around for a barn with straw instead, but if you make a thick enough layer, you can get away with the sawdust, that is if it comes from untreated wood.

I hope I have answered your question. Best spring wishes
Frederik
Danish garden enthusiast

Answer:  

Dear Line,
I agree that they are beautiful greenhouses. Tomatoes and strawberries need a lot of sunlight, so those are not optimal to grow. You can try with cherry tomatoes or heirloom tomatoes that tolerate less light. On the other hand, there are many other crops you can grow in the shade and pots. That is lettuce, spring onion, radish, parsley, rocket, potatoes, sage, chives, mint, lemon balm, kale, spinach and rhubarb.

Best wishes
Lars Lund  

Answer:

Thank you for your question. I have written an article about the topic here.
It takes some time to put up and take down, so I got tired of using it, as I am way too impatient. I gave it to my brother, and he sent it back to me, so now I have given it to DanChurchSocial. But it's a matter of preference. If you have the courage and are able to use it in the garden in the summer without disassembling it or have a storage space, it is definitely a really good option.

If you want a quick solution, put your pots on a thick polystyrene plate, bought in a hardware store. Wrap the pot well in a rug or whatever you have, possibly bubble-pack sheets. Cover the plant with bubble-pack sheets, a crop-cover cloth. If you have nothing else and it is urgent then use plastic, newspapers, etc., when there is frost, and take it off when the frost is gone. It is important that there is always air for the plant and therefore the cover should not be on for too long.

Best wishes
Lars Lund

Answer:

Hello Helle,
Lemon should be fertilized like many other plants when they start to grow and they need to be fertilized throughout the growing season, so you should definitely not neglect fertilizer while they are growing, and they are growing from April to August/September. Also remember that lemon is far better off being outside in the summer than under glass. That is why orangeries were built. In the winter, the orangery was heated with central heating and in the summer, the lemons was put outside. An orangery is therefore a heated greenhouse.

Best wishes
Lars Lund

Answer:

Hi Karin,
How exciting and not least delicious with a dwarf peach tree in the garden. There are many different sorts that all are interesting to grow and several of them are certainly suitable for pot cultivation. You write the sort must be tolerant to frost, to this I can say that the vast majority of peach trees in the trade are hardy and frost tolerant. With that said, they should still be protected during the winter and the pot should be insulated with a straw mat or similar.

The first sort I would recommend is the Crimson Bonfire, which gets beautiful reddish foliage, has slow growth and rarely gets taller than 4 to 6 feet. The sort bears many tasty fruits, is self-pollinating and should be tolerant to peach leaf curl. Bonanza could be another excellent option. The maximum height is 6 feet, it is also slow-growing and perfect for pot cultivation. Both Crimson Bonfire and Bonanza are created to bear fruit already in their early years of life.

Peaches bloom before leafing around April, with beautiful intense pink flowers. If you want to ensure delicious peaches in late summer, the flowers must not be damaged by the frost in spring.

Almost all sorts of peaches these days are self-pollinating, but there are rarely many insects in the air in early spring. To ensure pollination, you must act as a bee by using a fine brush or cotton swab and move pollen gently from flower to flower. When the fruit development begins, I can recommend fertilizing with tomato fertilizer, which has a high potassium content, a few times a month.

Peach trees can be attacked by the fungal disease called peach leaf curl, to prevent the fungal disease, you must avoid water and drops of water on the leaves until the beginning of May. The disease is seen by curly, discoloured leaves which must be removed immediately as the leaves quickly infect each other.

Good luck!

Best wishes Frederik
Danish garden enthusiast

Answer:

Hi Ann Marie,
I understand your question in the way that you want to make a greenhouse out of chicken wire or reinforcement mesh. You can easily do that, but it must be because you think it is beautiful and it can definitely be. There are greenhouses that are built from a lot of lists and are called shadehouses. In Sweden, I have seen houses where the framework is built of round iron, which reinforcement mesh is also made of.

If you want to do it to get a decorative element, then it is a great idea. If you pull a net over, you are free of almost all pests. However, it steals some light, but it only needs to be netted during, for example, the time the garden whites lay their eggs. Otherwise, vegetables thrive, as you know, in the open air and actually not very well in the greenhouse. You can also easily grow tomatoes in the open air. I do not grow mine in my greenhouse, but in the kitchen garden, and they yield delicious tomatoes. It just depends on the sort.

Raised beds with windows of plastic or old windows laid on top are also a solution if you want early vegetables. Here too there are many models, if you e.g., google the word garden frame. Pipes put in arches with a plastic sheet over also work fine, or with an insect net.

Caterpillars: usually it is early enough to cover around Midsummer Day, as it is usually only around the 1^st of July that caterpillars really appear. You can find a few larvae of large garden whites, in May and June and a few more in July, but the number does not culminate until August, and usually the last half of August.

Previously, one could buy a pesticide that killed the caterpillars, but it is not in the trade anymore. Otherwise, you have to inspect your plants and squeeze the eggs to death. If you have more questions, you are very welcome to ask.

Get well into the spring.

Best wishes
Lars Lund

Answer:

Dear Jan,
When I see the long stems, I immediately think: they lack light to a degree. In addition, they could very easily be exposed to something called root rot. Root rot is caused by several different species of soil-dwelling fungi. They attack the root collar and roots of herbaceous plants, which grow under adverse conditions, that is, too high humidity, compact and cold soil, which is not good. On the other hand, vegetable seeds should not be too hot. 10-15 degrees is best.

The attack of root rot is typically seen by a dark staining where the stem has contact with the ground, slightly below and slightly above. Eventually they dry out and become thread thin. The transportation of water becomes cumbersome, so the plant withers and dies. You can remedy this by partly using potting soil that has the right mix of gravel, that drains, and soil. Irrigate from below so the water is absorbed into the soil and use vermiculite in the top thin layer, it keeps the root collar dry. So, in your case, I think it's a mixture of lack of light and proper drainage in the ground.

Best wishes  
Lars Lund

Answer:

Hi Torben,
Thank you for your question. Mistletoe is a semi-parasite, which means it makes its own food from its own leaves, just like other plants, but because it can’t grow in the ground it needs to live on a host tree where it taps into the tree’s water and minerals. In general, mistletoe won’t kill a healthy tree but it can weaken it, and if the tree is old or sick mistletoe can cause problems.

The berries are spread from tree to tree by birds – the sticky flesh means the mistletoe seeds end up stuck to the branches where they germinate. Mistletoe particularly likes apple trees and it’s mainly found in the south and west of the UK, with high numbers of orchards.

Mistletoe can become a problem for trees if the bunches become too big and heavy, causing branches to snap, which can in turn make the tree vulnerable to diseases. Mistletoe can be pruned, in fact in the apple orchards of Worcestershire and Herefordshire they harvest the mistletoe and sell it at mistletoe markets in the run-up to Christmas.

A few groups of mistletoe on a healthy, large tree shouldn’t be a problem, but any more and they will have an impact on the growth and health of the tree. It’s therefore best to cut back the mistletoe growth in winter, it will however regrow, so you will need to remove the branches of the tree to reduce the number of mistletoe growths. Once you have a manageable number of bunches, cut back the growth every couple of years and check branches for new seedlings that have sprouted, removing these when you spot them. If the tree is tall you may need to get a tree surgeon to do the work.

Best wishes
Lars Lund

Answer:

Hi Anna,
The plant spirals hang from the roof of your greenhouse and are great for growing vegetables, such as tomatoes and cucumbers, offering support for their stems as they grow. Each spiral is made from an inner aluminium tube that’s covered in green plastic so that they’re strong and durable. The spirals look like springs but they’re not as flexible, and once you’ve pulled them you can’t shorten them, so slowly extend them to the required length – you may need an extra pair of hands.

Best wishes
Greenhouse Forum

Answer:

Hi Susan,
Thank you very much for your question. All the glass will need to be removed. If the glass is held in place with mounting strips remove these – you can save them or buy new ones. If the glass is fitted with clips, carefully remove these, popping them in a plastic bag or storage box. If the glass is fixed with silicone then use a knife to remove the glass. Remember to buy new silicone for when you come to rebuild the greenhouse. Pack the glass in a sturdy box, making sure that it can stand upright and that the glass is securely packed so that it can’t move about inside the box.

The greenhouse should then be removed from the foundation. It can be transported in one piece, just without the glass, on a flatbed truck or divided into sections and put in a van. It’s important to make sure the frame doesn’t move too much during transportation as the frame can twist out of shape. Make sure you keep hold of all the fittings and store safely for the rebuild.

The other option is to completely dismantle the frame. Make sure you mark up each piece so that you know where everything needs to go when it comes to reassembling it.

It will be easiest to have a new foundation made for the greenhouse so that it is securely anchored to the ground.

Of course, you could save yourself the time and expense of moving an old greenhouse and treat yourself to a new model for your new garden. Perhaps this is the opportunity to upgrade to something bigger or to buy a model that suits your new home and garden.

Best wishes
Greenhouse Forum

Answer:

Hi Inger, 
Thank you for your question. Scale insects can attach themselves to the stems of plants like vines and peaches. These pests suck the sap from the plants weakening their growth, so it’s a good idea to keep an eye out for these insects – they look like small, brown shells. Check the stems from late winter onwards and use a cloth dipped in rubbing alcohol, also known as surgical spirit, to wipe away any scales. With grape vines it’s a good idea to peel away any loose outer bark to expose any scale insects and other pests which might be hiding underneath.

Best wishes
Lars Lund

Answer:

Hi Natalie,
If the greenhouse is sitting on a cast base it should be safe to remove the slabs. However, you should be aware that the foundation may need to be supported, so it’s a good idea to remove a few slabs at a time and provide support where the slabs have been removed. Repeat until you’ve removed all the slabs and supported the whole structure.

Best wishes
Klaus Bisgaard Lillesø
Quality manager, Juliana Greenhouses

Answer:

Thanks for your question, Paula.
It’s a slightly blurry image, but it looks like common ivy (Hedera helix). It’s a clinging climber which can also be grown for groundcover. It flowers in autumn often when other flowers have gone over, so it’s great for providing bees and wasps with a late source of pollen and nectar so that they can build up their reserves for winter. Be aware that the plant is poisonous and can cause allergic skin reactions.

Best wishes
Lars Lund

Answer:

Hi Lisa,
Yes, these are suckers from the root base. Artichokes can be propagated from these suckers when the suckers are about 20cm tall in November or April, using a sharp knife or spade to separate the shoot from the parent plant. Pot them up into individual pots filled with a loam-based compost. Artichoke plants will be productive for several years but after this it’s a good idea to plant new plants.

It’s also a good idea to mulch the base of artichoke plants in autumn, using a thick layer of straw to protect them from the cold.

Best wishes
Lars Lund

Answer: 

Hi Christine, Thank you for your question. Yes, it is possible for plants to get too much light when grown under glass. Plants have evolved to cope with the light levels in their native habitat, so plants from the desert tend to have thick, fleshy leaves which can cope with high levels of intense light and heat. Whereas plants from cooler, more northerly locations will have adapted to make the most of the available sunlight. From May to mid-August it’s easy for plants in a greenhouse to overheat and for their leaves to be scorched by strong sunshine that’s intensified by the glass. Providing sufficient ventilation on hot days by opening vents and doors can help. You can also attach blinds or shade netting to the outside of the greenhouse or apply shade paint to the glass to reduce the intensity of the light.

Best wishes
Lars Lund

Answer: 

Thanks for your question, Kate.
Citrus fruit can take almost a year to develop to full size, and most cultivars form too many fruit for the size of the plant. These will often be naturally shed by the plant, but it’s a good idea on young plants to thin the number of fruit in each cluster to one.  

Don’t over water in winter and keep the plant in a pot that is not much larger than the root ball of the tree. Use a specially formulated citrus feed – high nitrogen from spring to midsummer and a balanced fertiliser between midsummer and autumn.

Best wishes
Lars Lund

Answer:

There are, generally, always moulds and fungi present in humid environments. Good ventilation is key, opening vents and doors to provide air flow. It’s a good idea to do this on mild winter’s days too, just for 10–15 minutes and make sure you remember to close the windows and doors.

Good plant hygiene is important throughout the year, making sure any yellowing or dead leaves are removed promptly, and dispose of any dropped fruit.

Overcrowding is a factor, so make sure there’s plenty of space in between plants for good air flow.

Take care when watering to water the compost in the pots and avoid splashing the foliage as this can encourage mould to grow.

Best wishes
Lars Lund

Answer: 

Toads in greenhouses are not uncommon. They like the humid environment and to eat the slugs and snails that inhabit the nooks and crannies of the greenhouse. They aren’t doing any harm, in fact they’re a natural pest control, so leave it alone. It’s worth bearing in mind that there are toxins in the skin of toads that are poisonous to pets, and it’s a good idea to wash your hands if you come into contact with one.

Best wishes
Lars Lund

Answer: 

These sound like the strawberry sawfly. They pupate and overwinter in the soil, so in April and May check the undersides of leaves for eggs and larvae and remove them by hand. After the plants have finished fruiting cut back all the foliage, leaving just the crown of the plant, and clear away plant debris.

Best wishes
Lars Lund