Lars Lund

08 Sep 2020 14:34

It’s dragging on

When can you transplant in the greenhouse?

Transplanting during frosty nights

May started with chilly nights. During the night between the 1st and 2nd of May, the temperature got down to minus 5 degrees. Greenhouse plants do not like frost, but some people have already transplanted tomatoes, cucumbers and peppers. 

I have heard about a woman who had lost all of her plants because of frost. Think about all the time she used sowing seeds, irrigating and taking care of the seedlings, and then everything is destroyed in one night.

You can buy tomato-seedlings to transplant in early April, and that’s why we are tempted to transplant too early.

I have asked established nurseries why they sell plants that early when they know the plants won’t survive without additional heat. The answer is always “Because everyone else sells them, so they are in demand.

What if they wrote, “Buy your tomatoes now, then we will take care of them until they are ready to be transplanted”.

Consumers are afraid that if they don’t buy the plants now, then there are none left in May. But there will be. What can be difficult to obtain are special seeds, that is, special kinds of seeds. Then you need to be early.


To find out what time is right to transplant you need an earth thermometer. You should purchase one of those.


Relevant to tomatoes the soil temperature should at least be 14 degrees during day and night. In most greenhouses, it will be that high around the 1st of May, but it can be difficult if there is still night frost. Cucumbers need more heat, they need 17-18 degrees, preferably 23 degrees. The temperature will normally be that high around the 1st of June. Pepper and chilli can profitably be planted in pots. They easily get infested with lice, so in pots, it’s to easy remove them and isolate them from others to get de-loused. Also, if the plant is planted in a pot you can easily bring it inside during the night and back in the greenhouse during the day. The optimum soil temperature for pepper and chilli is also 17 degrees. Make sure your chilli is in full sun and with lots of space around it.


There are more ways to guard the plants against chilly nights.


You have probably already removed the bubble wrap from your greenhouse, but you can use it to cover your plants.

You can also use a crop cover cloth for frost protection or purchase a mini greenhouse to put inside your greenhouse, then the area that needs additional heat is smaller.

You can also purchase a small petroleum heater; it will take care of the plants during the first couple of frosty nights.

Om Lars Lund

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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