The cold weather is vital for much in the garden, writes Val Bourne

This picture, above, taken at The Lost Gardens of Heligan, sums up the winter sleep when every- one’s garden takes a well-deserved nap. The dusting of snow, setting off this buxom Cornish lady, indicates the weather is crisp and cold — as it should be now. Thankfully, this winter is nothing like as wet and warm as last, so hopefully I’ll lose fewer plants.

Heligan is one of five gardens selected for a BBC award to be presen-ted at the Countryfile Magazine Awards ceremony this April. The shortlist, assembled by the BBC Gardeners’ World Magazine team, also includes Trentham Gardens in Staffordshire, the Royal Botanic Garden in Edinburgh, Alnwick Garden in Northumbria and Kew Gardens in Surrey. You can vote online at www.countryfile.com/awards2014-15, but they are all well worth visiting. I’m particularly pleased to see Alnwick there, because it’s imaginative and very well maintained despite being panned by the Style Police.

Most of us welcome a period of cold weather and we gardeners know that a prolonged cold snap will help to knock back slugs, for instance. However, ‘chill days’, when temperatures only reach 7°C are essential for many of our plants too. They become dormant, a state that allows a plant to conserve energy for the growing season. Apples require between 800 and 1,800 hours, according to variety. Raspberries and plums need roughly the same amount of chill hours as apples and currants just a little less. The pear is less dependent, but still needs between 500 and 1,500 — again according to variety. Chilling is not being frozen. The ideal temperatures are between 1.7°C and 7°C and apparently colder days below 1.7°C don’t count. The right amount of chill days increases the yield, because when warm spring weather arrives the tree has plenty of energy in reserve.

Lots of perennial and ornamental plants have chill requirements, especially the peony. This is why the tubers need to be close to the soil’s surface, only about two inches below, so that the cold can reach the growing tips and promote better buds. It was noticeable in my own garden that last year, following the warm and very wet winter of 2013/2014, that the number of peony flowers was much lower than normal. Roses also appreciate low temperatures, as do many spring bulbs. They all do well in my cold garden.

Ideally, a cool winter will be followed by a warm spring that arrives at the correct time. The worst scenario is when sunny March days reach 20°C by the afternoon and nighttime temperatures plummet towards freezing — as they did in 2014. Those extremes create hateful conditions for plants. Ideally, spring needs to creep in around the end of March or beginning of April with days that reach 13-15C and nights that stay in double figures. A warm spring is particularly important for fruit trees because it encourages the pollen tubes to develop, enabling good fruit set.

Climate change, a hot potato, seems upon us, for the seasons seem to merge together far more than they did. However, in 60 years of gardening, in three different gardens, I can remember very few perfect springs. Like most gardeners, I would love a crystal ball.

When the weather is clement apples and pears need winter pruning and this consists of creating an open framework with strong branches. Examine the shape carefully and then tip back the leading new growth, which will look shinier. This will encourage more new side shoots in spring and summer and these are pruned back in July or August to encourage fruiting spurs. Hopefully we will have a bumper crop — with more cool days to come.

No one could say fruit pruning is easy. I have three varieties of apple — ‘Blenheim Orange’, ‘Pitmaston Pineapple’ and ‘D’Arcy Spice’. D’Arcy is an octopus of a tree which I have been trying to shape since I planted it as a maiden (ie. a stick) eight years ago. I fully regret not buying a trained tree and wonder if I will ever get any fruit from this misshaped sea monster.

The ‘Pitmaston Pineapple’ is a short tree with many side branches, like a Jewish Menorah. It’s my best cropper and the small apples are adored by my grandchildren.

D’Arcy is upright and guardsman-like but every year the tall branches reach for the sky. The step ladder is needed to cut back and restrain the uprights. This has cropped heavily in the past, but last year it was poor. Not enough chill days?