Sandy’s Garden ... My rhubarb likes the frost

Sandy Simpson
Sandy Simpson

There are words that most gardeners dislike hearing a weather forecaster use.

“An area of high pressure is bringing clear skies and light winds to the whole country, with pleasant sunshine for most of us during the daylight hours and a moderate to severe frost almost anywhere tonight. Towns and cities will generally be down to minus two to minus four degrees, with rural areas several degrees below that.” Brrr! And that’s not good news for many plants.

But my rhubarb will benefit from a real touch of frost, for established rhubarb plants need temperatures of below 5°C if they are to produce the tasty shoots for which we grow the plants in our gardens, the plant’s very raison d’aitre to the gardener.

Rhubarb is a plant that always prefers cooler weather to warm temperatures, is very much at home during a hard winter and doesn’t mind long dry spells either.

It likes growing in Scotland, for it needs an average summer temperature of less than 25°C - say, 80°F - to allow it to grow vigorously, and we can guarantee that it won’t suffer from excessive summer heat here!

As virtually everyone knows, we eat the stalks that spring from what is called a ‘crown’, which is made up of fleshy rhizomes and buds. The rhizomes are the plant’s roots, “continuously growing horizontal underground stems with lateral shoots and adventitious roots at intervals”, to quote the Concise Oxford English Dictionary. And adventitious roots? These, according to the same reference work, are roots that “happen by chance”, or what we might call ‘random roots’.

These are the underground stores and resources that see the plant through the winter safely. And, come the spring, the first buds appear in the crown, encouraged by the longer hours of daylight.

But rhubarb needs cold weather and, ideally, frost to convert carbohydrates into glucose and help the buds to grow, the shoots then emerging sequentially as long as temperatures remain moderate, which, in our case, means all summer long in the case of mature plants - plants that have been established for at least a couple of years.

Again, as almost everyone knows, the technique is to cut the grown stalks close to the soil or simply pull them out individually. All of the stalks of a plant may be harvested at one time, or they may be pulled out selectively as they are wanted.

After harvesting, remove the leaves and enjoy in whatever way you like, from eating raw dipped in sugar, through stewing to make a delicious dessert or baking into crumbles and pies.

But, although rhubarb does need cold temperatures to get it to start growing, really severe frost is bad news for this plant as for so many others. Severe cold can result in oxalic acid crystals which are naturally present in the leaves migrating to the stalks, which may make the stalks poisonous. Fortunately, we get a clear warning of any such problem, for affected stalks become soft and mushy and should not be eaten. However, even after a late spell of severe frost has caused the plant’s leaves to become black or brown round the edges, stalks that are still firm and upright can be eaten in complete safety.

However, my own rhubarb has not yet grown sufficiently to let me have a ‘pulling’ and I am still dependent on finding the plant in the fruit and vegetables section of any of my local supermarkets. Until quite recently, any that I did find had been imported from Holland. But the cold snap in the middle of January affected Yorkshire in the same way that it affected Stirlingshire; and the significance of that is that the ‘pink triangle’ - the area of West Yorkshire bounded by Bradford, Leeds and Wakefield where the finest English rhubarb is grown - enjoyed some frosty nights, to the delight of professional rhubarb growers. Hooray!