91av

IN MY garden, bulbs such as snowdrops are coming up. Every year, I wonder if spring is arriving earlier due to climate change.

One , such as plant species unfurling their leaves, had been hastened by 7.5 days across Europe in the previous 30 years (Global Change Biology, ). And research published this week has found that UK plants are flowering nearly a month earlier than they did before the mid-1980s, probably due to warmer temperatures from January to April.

You might think that warmer weather would be welcomed by gardeners, but some plants, particularly fruit trees and bushes, require a period of cold before they break their winter dormancy, so warmer winters could lead to worse crops. In the UK, blackcurrant bushes may be especially vulnerable, although new varieties are being bred to tolerate a warmer climate.

Early springs are good for many crops, as they extend the growing season, letting you sow seeds and plant seedlings earlier. But gardeners need to beware of late frosts, when an unexpected cold spell means temperatures overnight fall below freezing, which can blacken foliage and kill off tender plants.

After a few disasters, including a year when I lost my entire crop of new potatoes, I now keep a close eye on the weather forecast. If plants look in danger, they can be protected by overlaying them with a thin sheet of fabric called horticultural fleece. In a pinch, old sheets or net curtains will suffice.

Another option to protect new seedlings is a cloche, a transparent dome that creates a miniature greenhouse around a young plant. You can buy them or make your own by cutting large soft-drink bottles in half and pushing each dome firmly into the soil. “You’re bringing a plant on by changing its microclimate to a warmer one, so it will grow and develop faster,” says Tim Sparks at the University of Cambridge, who was involved in both the 2006 study and the new flowering research.

If using cloches, you must keep a close eye on the weather, as a sunny spell could mean young plants overheat and dry out to a husk. But if you use the top half of a bottle, you can put the cap on and off to ventilate or keep heat in as needed, without disturbing the plant.

I use these cloches for seedlings of peas, beans and ornamental sweet peas, among other things. Depending on where you live, you may soon be able to start sowing sweet peas indoors in small modules for planting into the ground or large pots outdoors later, under bottle cloches. When the weather gets warm enough, or the plants too big, remove the cloches and stick bamboo canes into the soil for the plants to climb, helped by regular tying in. Three canes lashed together make a sturdy tripod structure.

For other projects visit newscientist.com/maker.