Sometimes December creeps by without much troubling the winter inhabitants of the greenhouse, which in my case are sort-of tender aeoniums and pelargoniums, and a couple of other tough succulents. But this year has been different. Winter has come on hard, with frosts and snow and many days and nights of sub-zero temperatures. These plants are well tucked away, and I keep the mini greenhouse that they are in close to the house, which I hope staves off the worst of the cold. But still I have been concerned that this isn’t enough these past couple of weeks, and have brought in some other measures to see them through.
My go-to for keeping this greenhouse heated has always been a propagation mat, which is plugged into the mains and emits a very low but constant heat and is just enough to keep any frost away but without actually heating the place up. With electricity prices being what they are though, I decided to try another method – a terracotta pot and tealight heater – and it seems to be working well.
This is an entirely DIY method, and chances are that you have everything you need to hand. You will need: a candle that will burn for at least eight hours – I am using some extra-large tealights but a pillar candle would work really well too; a safe base to stand it on, such as a dish; three brick fragments or similar; two large terracotta pots, one small enough to fit inside the other; two pieces of flat terracotta or large coins and a few pebbles.
The idea is that you place the candle on a safe surface and then place the smallest terracotta pot upside down over it, but sitting on the brick fragments to allow oxygen in. You then block up the drainage hole using the coins or the terracotta, or even a pebble. Place a few more pebbles on the upturned base of this pot to create space for air to circulate and then place the second, larger pot upside down over this. Block up its drainage hole too. The candle slowly heats up the inside pot, which in turn heats up the outer pot and both act as a small radiator, keeping the worst of the chill away. It has worked a treat over the cold spells of the past weeks.
It is also a great idea to throw horticultural fleece over all of your plants during these cold times (taking care to keep it well away from any bare flames of course) and to really tuck it in and around the plants. Pull plants away from the glass and tuck fleece between them and it as well. As my greenhouse is so small I can also throw blankets over the whole thing, temporarily, just while the weather is particularly cold, and while this wont be possible with a larger greenhouse, do consider making little inner compartments within your greenhouse within which you can put the more tender plants. You can use a clothes horse for this, covered in blankets, or make a frame especially for the purpose.
While you of course don’t want to be blocking out light in this way all winter long, these cold snaps rarely last particularly long and it is really worth throwing everything at keeping your plants alive and unharmed through them so that you can then peel off all of these layers and let them get a little winter light. But even once milder weather comes, remember to keep all of these techniques to hand for the next cold snap, which is bound to come along sooner or later.