It's been a cold couple of days. I've run the heaters in the greenhouse and conservatory for the past two nights, and left them on all yesterday, partly because it was so cold and partly so that I wouldn't forget to switch them on again when I got back from the concert. It would be a terribly expensive business if the whole winter was like this, but tonight will be only the fourth I've had to use them, and it is forecast to be safely back above freezing by the weekend. When you look at the price of plants, and tot up the replacement cost of my half dozen Geranium maderense alone, you can see that except in the longest and most savage winters it pays to keep some growing space frost free, quite apart from the fact that I am attached to my plants.
I used to be much more hawkish about switching the heaters on if the forecast was for anything below zero, but experience has taught that the glass is enough to keep the odd night of frost out if the thermometer only dips to minus one or so. The kind of weather that produces overnight frosts tends to also give us sunny days, and there is some thermal gain to be had under glass even in the winter. Plus, as Peter Gibbs explained in his talk to my Plant Heritage group a couple of years ago, the earth acts as a great reservoir of heat so if you cover it with glass or plastic or even fleece you can hold in enough of the warmth to protect your plants from light frosts. It gets trickier when there is a whole run of freezing nights, and I imagine the heat gradually being sucked out of the concrete base of the greenhouse and the brick wall at the back of the conservatory.
It helps being fairly close to the coast. I've seen reports of minus eight degrees at Writtle outside Chelmsford, and I'm sure it didn't get anywhere near that cold here. I don't know how cold it did get because I don't have a garden thermometer, but if it had got down to minus eight various things would be brown and dead. It also helps that it is only January and not late February after a mild spell to lure plants into growth. Cistus that have made it unscathed through a normal winter can have their new leaves badly scorched by even moderate frosts once they've started back into life. They generally grow out of it, but it is depressing to suddenly have to add Trim out dead Cistus shoots to your already long list of Things to Do. Our climate allows us to grow an amazing range of garden plants, but one reason why species from places with distinct Continental climates can suffer is that they can't cope with the start-stop-go-stop English winter.
The witch hazel flowers are not bothered by frost. I went and stared at them this morning from a polite distance, because by then the frost had melted to leave a very soggy lawn and I knew from bitter experience that the suede boots I was wearing would become soaked through within seconds if I trod on the grass. The Systems Administrator went out while the frost was still encasing every branch and stem to take some photographs. I think the SA knows better than to have walked on the frozen lawn, but if not the blackened footprints will give the game away in due course.