How to get early potatoes in the greenhouse
At one time the potato was something you would feed the pigs with, but today it is almost like gold, and we fight so valiantly to get the gold and be among the first to get it. You can easily join this fight when you have a greenhouse.
The easiest way to cultivate potatoes in your greenhouse is to use a container. It does not matter whether it is an old rain boot (which by the way can be quite decorative), a large biscuit tin, a plastic bag or a bucket as long as there is a drain in it so the water can drain away.
How to do it
Choose an early sort
There are several hundred different varieties of potatoes, but you need to get hold of those that are the earliest to crop.
I will recommend: “Solist”, “Hamlet”, “Frieslander” and “Sofia”
Seed potatoes or your own potatoes
You can use your own potatoes from your garden or table potatoes you have bought. If you choose to use your own from the garden, you must make sure that they are free of diseases. If they are not, they can infect your new potatoes. You can also buy seed potatoes which are not infected with any viruses, but they may have other plant diseases so check that they are healthy-looking before you buy them. Seed potatoes should have a medium size.
To pre-germinate means that you prepare the potatoes for sprouting. Sometimes the potatoes have already begun this process when you buy them. There are two ways.
The first method says that you can place them somewhere dark and with a temperature of 22 degrees for 14 days. When the shoots are 5 cm long, they are moved to somewhere with more light at a temperature of 15 degrees. Hereafter they are ready to be put outside after a couple of days.
A more common method is to place them somewhere with light at 16 degrees Celsius for 6 weeks. This makes the shoots thick and they do not easily break. But both methods work, and if you want, you can try both and see what works best for you.
Transplant in buckets
When your potatoes have been through the pre-germination process, you can transplant them to buckets.
The benefit of this is that you can take out the buckets in case the potatoes are not ready when you are about to transplant tomatoes. Tomatoes and potatoes together are not a good match.
The first thing I do is to fill the buckets with soil. Then a lump of sheep wool (not a must), the potato on top of the wool and then soil again. Wool is good to store water even when it is being decomposed to fertiliser.
Boe Jørgensen, an experienced Danish horticulturist, shares the method he uses when cultivating in the greenhouse.
First week in March
- Place the pre-germinated potatoes in milk or juice cartons without a bottom and with some topsoil the first week in March and place them in a plastic bucket filled with 5 cm peat.
- Plant the potato in the middle of the carton with soil on top and under it.
- Soak the soil in the carton and place the bucket somewhere inside the house where the temperature is between 15-20 degrees.
- The peat in the bucket should always be fairly moist.
Between 25th and 28th March
Now the potatoes can be transplanted to the greenhouse. This is done in 12 litres buckets with compost. Remember to irrigate. (Boe has an automatic irrigation system). Especially while the potatoes are forming tubers, they should never be in need of water. Potatoes are not frost resistant so if there is a chance of days or nights with frost they must be covered. You can for instance use bubble wrap. One time Boe had to use a warming cable. Alternatively, you can use a greenhouse heater. Should they get damaged by the frost, then the buds will start coming up again, but this will delay the project.
Potatoes are ready to be harvested 15th May.
From pre-germination to transplantation 5-6 weeks
From planting to harvesting 80-100 days
The potato sort determines the usage
The potatoes that most of us know are the potatoes called table potatoes.
As previously mentioned, there are many potato varieties. And some sorts are more suitable for mash or backed potatoes compared to those you use for boiling or roasted potatoes. If you make backed potatoes, it is best if they are not too firm. And if it is for mashed potatoes, they must be able to become mushy after they are boiled.
Om Lars Lund
Danish horticulturist and journalist
Lars Lund has for many years engaged in the garden and greenhouse. Lars has published many books about greenhouses, and he has participated in many Danish horticultural TV shows. He is a walking garden encyclopaedia, and he has answers for most basic cultivation questions – also the more ambitious ones.
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