Cracking tree growth

For a shady refuge on a very warm day, a good tree to seek out may be a walnut, for it has the widest spread canopy in relation to its trunk of any of our broadleaved trees. This is just one of the many attributes of the walnut tree juglans which is appreciated by nurserymen for producing delicately flavoured nuts, by craftsmen for the quality of its timber, and by gardeners and landscapers for its attractive appearance as a feature of many grounds and public parks.

Just how much their own walnut trees mean to those householders and landowners fortunate enough to have one or more on their property was shown in their enthusiasm to have included them in a project in 2000 to map their distribution throughout the country. So great was the response that several thousand were received.

"It really caught people's imagination," says Karen Russell, a member of the group of horticulturist growers, processors and timber merchants which launched the initiative.

Research was, by then, already taking place into the most suitable varieties of walnut for commercial timber and fruit production. The centre for the trials for timber is in Oxfordshire, at the Northmoor Trust, while many of those for crop production are taking place at East Malling Research in Kent.

Jo Clark, forestry officer of the Northmoor Trust, oversees trials for which over 2,200 young trees are growing, on three sites that of the trust at Little Wittenham, at Upton Wold, near Moreton-in-Marsh in the Cotswolds, and in Somerset. Similar work on black walnuts is also being carried out in the National Forest area of the East Midlands, at Lount Wood, near Ashby-de-la-Zouch, which also has the largest collection of walnuts in the UK.

In recent years, the volume of wood produced in the UK has been small in comparison with that imported, with increasing pressure on consumers not to purcharse tropical hardwoods and strict control on their importation, an equally inexpensive, homegrown alternative is needed.

This is the need that the Northmoor Trust is helping to address, by research into individuals within the species that can provide the forestry industry with planting stock of improved and tested quality. It is seeking to identify the best provenance of many broadleaved species for optimal growth in this country.

The walnut trees are growing from material collected all over the world, including from China, Turkey, Kurdestan, South America and the home of walnut growing, California.

At Little Wittenham, there are 375 different varieties of the common walnuts juglans regia 55 of the black walnut juglans nigra and five hybrid varieties.

Because of the British climate, young walnut trees can be difficult to establish. They are also intolerant of competition and need to be widely spaced.

One aspect of the Northmoor Trust's research is into the benefit of growing a 'nurse' crop which provides shelter and protection from frost damage and creates a micro-climate of humidity around the young trees.

The protection from frost is particularly important, for if the terminal bud on the leader, the central upright stem, is affected, this causes bad formation through the leader becoming forked rather than continuing to grow straight and true.

Two 'nurse' crops being trialled are Italian alder alnus cordata and the short, bushy eleagnus umbellata, another species of the eleagnus often grown in gardens. These are nitrogen-fixing trees, which fix atmospheric nitrogen and make it available to the walnut trees growing with them.

Ian Bond, owner of Upton Wold, has long had an interest in the trees. He has established an arboretum, entirely of walnut, in which some 160 of the 170 trees are of different varieties. Last year, this arboretum was given recognition as one of the National Collections of Juglans.

The collection contains 14 of the recognised species in the world, the other seven, of which Mr Bond would like to obtain examples, are South American.

The arboretum and the gardens of Upton Wold can be visited by the public and by appointment. They are also open during the summer months through various open-garden schemes.

Visitors can see the collection, the first trees of which were planted in the early 1990s, with more recent plantings which are still in earlier stages of growth. The area with trees growing as part of the trials is not open.

Walnut trees can live up to 200 years. If used for timber, they can be sufficiently mature in 60 to 70 years. If grown for their crop, they can, according to variety, be productive in about seven years, or may take twice that time to become economically fruitful.

As well as these two uses of the walnut tree, on which attention is now being focused, there have, over time, been many more. These include as medicinal remedies the walnut is one of a popular range of flower remedies the leaves in the brewing of wine, and the oil from the ripe nuts in cooking.

The green husks, leaves and mature husks, and catkins can produce dark yellow, brown and golden brown dyes respectively. The oil has been used for making varnishes, polishing wood, in soaps and as lamp oil. The nuts can be used a wood polish, as the rubbing releases the oils.

The dried husks have been used to paint doors, window frames and such areas as a preservative, the protection for the wood being thought to be due to their tannin content.

In the past, many villages had their own walnut tree. The reason for this was that the leaves contain juglone, which is insecticidal, and they therefore act as an insect repellent. Horses would have been rested beneath these walnut trees to relieve them of insect irritation.