VAL BOURNE says now is the time to plant the very valuable rhubarb

Many years ago, in a lowly research post, I worked on rhubarb, a valuable crop if forced into early growth. The stems are rose-pink, the foliage crinkly yellow and, when it's cooked, it's an ambrosial food quite unlike the garden-grown, acidic rhubarb that appears later.

Cawood in Yorkshire is the centre of the rhubarb forcing industry. One nursery there, the Brandy Carr Nurseries (01924 291511/www.brandycarrnurseries.co.uk) stills hold the largest collection of varieties in Britain. They sell plants too.

But in the late 1960s the crowns in the forcing sheds were failing to perform as the result of a virus and the industry was threatened. Our research team went to take samples in the dark, damp and warm sheds over several years. I can still recall the cathedral-like atmosphere inside, where the silence was only broken by the occasional, very-gentle plop as the bud scales split under the pressure of another stem pushing through the ground.

Raising the temperature kills a virus. When we have one our body responds by giving us a temperature to ward off the virus. Plants can't do this for themselves. But we used tissue culture - or micropropagation - to artificially heat the plant material and the crop recovered. Within five years the stock plants were clean and once again vigorous.

Gardeners can emulate the damp, dark atmosphere of a commercial shed by using a rhubarb forcer, whether its the stylish sort made by the iconic Whichford Pottery or, as in the picture, a pair of old dustbins. Packed with straw and put in place in November, new stalks will appear by February, especially if you use Timperley Early'.

Susan Campbell, in her excellent A History of the Kitchen Garden, tells us that in the 18th century rhubarb "was a novelty" and likely to be used more for medicine than for culinary purposes. Chinese herbalists were grinding up the dried roots into a powder as early as 2700BC. Anyone who has ever eaten a large bowl of fresh rhubarb will probably be able to guess the reason why the Chinese used it. It's a purgative.

But by the 16th century large amounts of money were spent importing the powder as rhubarb only grew naturally in China, Siberia and the Himalayas. Rha' is actually the ancient name of the River Volga in Russia and gives the plant its generic name.

The government was concerned about the amount of money leaving British shores and in 1763 the London Society for the Encouragement of the Arts, Manufactures and Commerce offered a gold medal to the person who could raise the most plants. The medal was given to Sir William Fordyce who raised 300. By 1815 the rhubarb tart had become a popular dessert on the menu.

When the Sugar Tax was repealed in 1874 rhubarb gained even more in popularity. One wonders whether the practice of putting a Sweet Cicely leaf (Myrrhis odorata) was an 18th-century practice. It certainly cuts down on the amount of sugar needed.

The variety Victoria' is slightly later and has very red stems. Another called Grandad's Favourite' was introduced by Alan Bloom, of Bressingham, a man who lived until 97 and ate rhubarb for breakfast for most of his life. Sometimes I got to share a bowl and talk plants.

Now is an excellent time to plant a new rhubarb because every garden should have a clump.

I am taking part in a Gardeners' Question Time on Wednesday, March 19, at Exeter Hall, Kidlington, with Bob Brown and John Graham, in aid of Bridewell Organic Gardens. Tickets include refreshments. Tel 01993 868445 or 01869 350155.