It might be autumn, but Jean Vernon is starting to hunker down for winter and preparing her greenhouse for cold weather
I know it’s October, but this year has really flown by. The pandemic has brought every day into focus and yet when I look at the calendar I seem to be turning the pages faster than the month is out. The clocks change at the end of October and already the temperature is starting to go into single figures. I fear the sub-zero chill is close as the light fades and the clocks change and the leaves hit the deck, or the lawn or the borders.
I love the autumn but the gentle slide to winter comes all too soon, and while I try to embrace the wonders of winter, sometimes it does cause a few issues. In a normal year I am always chasing my tail and this year is no different. I feel better prepared in some ways – we are very rural and usually get snowed in if there’s snow, so a stock of supplies is always essential. I’ve already made a cake! And I’ve moved the begonias into the greenhouse, carefully removing their fading blooms and falling leaves as they start to senesce for winter.
Winter greenhouse preparations
I don’t heat my greenhouse. To me it seems a total waste of precious energy heating a single glazed building that will lose its warmth quickly in cooler weather. But I do use my greenhouse to overwinter many tender and half-hardy plants, and more. Sometimes it’s not the cold that’s the problem, but more the damp. Many half-hardy plants need a cold dry winter to survive. It’s a tricky balance ensuring the glasshouse is ventilated and airflow is good and not too cold.
I use a variety of techniques to help see them through the colder weather. First I am lucky that I have auto vents in my greenhouse. They don’t open much in the winter, but when there is a warmer sunny day and the glasshouse heats up the vents will open to let the warm air out. I have vents low down in the greenhouse wall, which allows air to be drawn in at the bottom and vented at the top, this mimics natural airflow.
The biggest enemy in the autumnal greenhouse is grey mould/botrytis. It quickly affects dying foliage and can also affect healthy plant tissue. Keep it under control by pruning out affected leaves and stems and remove them from the greenhouse. Check daily to stop a small problem escalating. Tidy up any dead leaves or plant material and reduce watering and increase airflow as much as possible. And don’t forget to turn off your water supply at the mains and drain the system to stop the pipes freezing in the cold.
Plants are spaced out and where possible planted in terracotta pots that will hold any heat, allow compost to dry out and hold on to any warmth. Some of my begonias are contained in double skinned metal planters. I find that the air between the layers acts as extra insulation and protects the plants within.
Many of my pots of precious plants are placed into polystyrene trays salvaged from over packaged parcels and stored for just this use. This insulates the bottom of the pots and helps prevent the roots and soil freezing. I’ve got a stash of horticultural fleece and giant bubble wrap that gets thrown over the top of plants in extreme cold, but I also find that the brick lined stone support walls and the terracotta tiled floor do act as radiators, holding onto any warmth and releasing it back slowly.
The protection of the greenhouse is usually enough to see my most precious tender and half hardies through the winter. In twenty years I’ve never heated it and have rarely lost any plants. It’s the winter residence for my lemon verbena, scented pelargoniums, fuchsias, ginger rosemary, ornamental salvias, begonias, and always a range of cuttings and the odd houseplant too. It’s a risk even in a milder winter, but I find any glimmer of winter sunshine takes the chill off the greenhouse and if I am careful about not letting the heat out when I open the door, then most plants will make it. And all being well, there is the promise of Christmas potatoes, herbs to harvest and winter kale, rocket, peas and broadbean shoots to eat.