Lars Lund

08 Sep 2020 14:34

Late summer and winter tips from the castle gardener to you who grow exotic plants

When approaching September citrus plants and other exotic plants that we have outside need to be put inside. Before you do that, here are some tips from a specialist.

By Lars Lund

Kirsten Engholm has a lot of experience with plants for the orangery. Naturally, we have asked her which plants people from The Greenhouse Forum should plunge into.

Kirsten answers that it is important to have the right space for the cultivating and overwintering conditions. Additionally, you need to be aware of how much sun there is in the garden, how much shelter and how to nurse the plants. The easiest way to decide that is to acquaint oneself with the requirements of each plant. It is, for example, no fun growing lemons if you don’t have anywhere to put them during the winter, and then is forced to buy a new plant every year. Hence, overwintering conditions is something you should consider at first.

You can get a long way with a room you can keep above 5 degrees. Then the plants don’t need to be put in a dry living room. A frost-free sunny basement is better.

Be careful with the root system

The root system is maybe the most sensitive part when growing in tubs. It is of great importance that the root system is protected from frost. You can do that with an insulation mat, straw or sackcloth.

Lighting and temperature conditions should be in harmony. The colder it is the lesser light plants can tolerate and vice versa. Also remember that when plants are put outside in spring, they can easily get burned by the powerful sun, so make sure to provide shade in the beginning, says Kirsten. You can do that with a crop cover cloth if the garden does not provide natural shade.

When the plants have hardened, they are more tolerant to full sun or shade. They thrive better when sheltered.



Some plants die from fungi during the winter. Therefore, you need to be aware of the humidity. High humidity can be lowered by raising the temperature or, even better, airing out, depending on the temperature outside. If the temperature outside is too high, airing out does not help much. Citrus plants and many subtropical plants thrive in humidity between 50% – 70%. If it is very dry the plants need to be sprayed.

For how long can the tub plants stay outside?

It depends on which family and sort it is, says Kirsten Engholm. The hardiest orangery plants like bay laurel and laurustinus can stay outside from April to November, while citrus generally can stay outside from mid-May till the end of September.

Plants are most sensitive to coldness when they are put outside in spring. During the fall they gradually adapt to the cold temperatures. In spring it is important to harden the plants.


How often should the tub plants be transplanted?

Every 3-5 years they should be transplanted. If you wait too long the root system can get so powerful that the plant is difficult to get out of the put or tub. The best time to transplant is in the late winter months, while the plants are chilling. When transplanting Kirsten cuts the roots between one third and a fourth. Though it depends on the plant. The root system of citrus plants develops very slowly, so they should probably not be cut, while fig and agapanthus have a large root system.

You would think that the bigger the pot is, the better it is for the plant, but it is not necessary, says Kristine. Generally, you should not transplant in a pot that is more than 20% larger than the current one. Remember not to cover the root collar with soil. It will weaken the plant for a long time. Also, remember to drain the pot. Lastly, buy the soil that fits the plant.

Should citrus plants be pruned?

Most orangery plants can be pruned in the winter, but also at other times. Generally, the principle is the same as for other fruit trees we know. Remove the dead branches, thin out in the middle and shorten the long branches by 1/3, and finally, remove basal shoots.


How much water should the plants get during winter?

You can easily irrigate too much during the winter. The soil should dry out before irrigating again. Plants that overwinter in 5-10 degrees should be irrigated every 1-2 weeks. Be aware of the pH value when irrigating with waterworks water. Calcifuge plants cannot absorb iron and manganese if the pH value is above 6. Irrigate with rainwater or boiled water if you live in area with chalky water. During the summer you can adjust the pH value with liquid fertilizer.