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Lars Lund

08 Sep 2020 14:34

Protect your plants from frost

It is about making it warm and cosy for the plants.

Photo: Grøn Kommunikation

 

We are heading towards winter and the meteorologists forecast night frost. It does not seem to be right away, and inside the greenhouse, it will hardly do any harm. But night frost is a sign that winter is now on its way. I will therefore give you my three easy solutions to keeping plants frost-free.

 

1. Make your greenhouse smaller with bubble wrap.

If you have a large greenhouse, build a smaller corner of thin battens and put bubble wrap on battens and windows, so that the room is closed, but with a loose entrance like a curtain. Remember it must be bubble wrap with large bubbles intended for insulation and not the small ones intended to withstand shocks. Such an arrangement can easily keep the frost out down to minus 5 degrees. If the frost gets harder, you must have a small heater inside. I use a small gas oven that regulates the temperature according to how hot I want it.

You can also lower the ceiling with some steel cables and put bubble wrap on them, as well as insulate the whole house with bubble wrap if you have many plants to protect. Place the potted plants on a thick flamingo plate and if necessary, wrap the pot in bubble wrap. If the pot freezes, there is a great risk that the plant will die, but if the roots are protected, it will survive or shoot what is above the ground again.

 

You can make your greenhouse smaller and easier to warm up by lowering the ceiling with bubble wrap.

Drawing: Torben Hyldgaard

 

2. Build a plant hotel

Another solution I also use is a small shed. Lay out a four-inch-thick polystyrene flooring on the floor. Insulate walls and ceiling with at least 4 inches of insulation. Put in a double-glazed window so that light can enter. Put in an electric oven that turns on when the temperature is below 5 degrees. It will very rarely occur at all that extra heat will be needed. The warmer it is, and the brighter, the more water the plants need. The ideal heat for the vast majority of plants is between 8 and 12 degrees. Remember to ventilate by opening the window and door when there is no frost.

 

If you don’t want to build your own plant hotel, then many nurseries offer accommodation for plants.

Photo: Grøn Kommunikation

 

3. Put your plants inside

I have a chilli Bishop Crown that I let overwinter in my bright bathroom. My kumquat and another citrus are in the bedroom where it is bright, and the temperature is around 17 - 18 degrees. It's going pretty well. I leave the olives in the greenhouse and wrap the big ones with bubble wrap around the pot and on top of the plant. My agapanthus - of the type that does not tolerate frost - has been in my plant hotel for many years, but because it has become very large and full, it is somewhat squeezed, and then plants rot very easily. Therefore, the last two winters I have placed them under a pent roof up against the house wall to the west (may also be south, but my terrace with a pent roof is west facing) and covered with loose bubble wrap, which is removed when there is no frost. If there is severe frost, the leaves turn yellow-green, but they are fine when spring comes.

 

They take up much room, so I put the South African lilies under a pent roof with bubble wrap covering the plants.

Photo: Grøn Kommunikation

 

This strong thing gets to overwinter in my bathroom.

Photo: Grøn Kommunikation

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.  

Get to know Lars Lund