Frozen Veg
Even within the warm, fuggy microclimate of central London, the last week or so has been extremely chilly! I went to water some plants one morning last week (they had been drying out beneath a cold frame) and found steam rising into the air, not because the soil was warm so much as that the air was freezing.
A frosty garden is so beautiful, but at the same time slightly nerve-wracking as too often when the sparkling crust melts it leaves plants blackened, collapsed or reduced to a sad-looking mush. Plants are up to 95% water and this water is held in the cytoplasm within plant cells. As any party host who has accidentally left a bottle of wine in the freezer overnight knows, water expands as it freezes and can burst the walls that bind it, shattering a glass bottle in the freezer and the walls of a plant cell. Even before this point, ice crystals can interfere with the workings of a cell, and freezing and thawing can cause bubbles to form inside the plant’s xylem. All-in-all, not good!
Frost hardy plants have some ingenious mechanisms for coping with this and, triggered by dropping temperatures through autumn, they’ve been busy preparing for these frosty mornings without us even noticing. Some plants produce antifreeze proteins which interfere with the development of ice crystals while others pump water out of vulnerable cells to be stored elsewhere (the roots for example). A third coping strategy is a gift to the vegetable gardener: plants fill their cells with sugars to reduce the freezing point of the solution within them, either converting stored starch into sugars or pumping sugars up into their leaves (depending on which organs the plant wants to save). Vegetables that use their roots to overwinter (think carrots and parsnips) are sweetened by frost as the starch within them is converted to sugar. Meanwhile, brassicas fill their leaves with sugars, so the season for kale and sprouts is upon us and cabbages and kale look as perky as the day they were planted. If you’re reading this from a frozen part of the UK with much colder temperatures than I have here, at least you can console yourself with the fact that your vegetables will probably taste better for it!
Sweet Kale shoots picked hours after a frost
My oriental salad leaves are hardy enough to see through a London winter, but to give them a bit of extra protection Toby built me some wonderful cold frames last year and they are now huddling beneath them with a slight advantage over the open beds. But just because plants can survive doesn’t mean they’re loving it. All our salads have been creeping along, growing almost imperceptibly in the dark and cold, but this is about to change! We’re now well past the winter solstice and by the end of January we will benefit from an extra hour of sunlight a day. Plants sense this shift, cease their sulking and begin to grow again, so we’re approaching the point at which leafy greens will put on enough growth to be worth harvesting.
Mustard ‘Red Frills’
Unfortunately, just because we have more daylight it doesn’t mean things will get any warmer. Like a stone baking on a hot beach, the earth absorbs heat during the day and emits it at night. In summer when days are long the earth stores the heat, and then emits it (like underfloor heating) during the dark winter. As long as the heat we absorb from the sun each day is less than that which we lose at night, temperatures will continue to fall.
So it’s hats and coats on for a while yet and our cold frames are staying in place, but at least we know that everything is beginning to grow beneath them, and they’re gradually warming the soil for the first, early seeds in the weeks to come.
