Soils and climate
Cobnut trees are hardy and grow well on a wide range of soils except those that are waterlogged, but like all plants they grow best in soil conditions that suit them. They prefer a good friable topsoil overlying a free draining substrate. A soil that is too fertile will tend to produce trees with excessive vigour, which will not crop well. However, it is still possible to grow reasonably sized and cropping trees on stony ground as long as there is sufficient soil and good drainage. A neutral to alkaline soil is ideal, but cobnuts also grow well in more acid soils.
Cobnut trees can be grown as far north as Scotland, but they crop more regularly further south. They can readily be grown in gardens, but if you have grey squirrels they may eat them before they are ripe.
Flowering and pollination
Cobnut trees produce separate male and female flowers. Only the female flowers can develop into nuts, and then only if they are fertilised with pollen from the male flower.
The male flowers are yellow catkins also familiar on hazel bushes in hedges and woods. Each catkin produces millions of grains of pollen which get distributed on the wind. Varieties differ widely in the time they shed pollen, from the New Year until March in the south of England. The female flower is a tiny red tuft. Again, the time these are produced depends on variety, and the catkins and female flowers may not be out at the same time.
Cobnuts are largely self sterile - the pollen from a given variety cannot pollinate the same variety. If you live in the countryside where there are plenty of wild hazels nearby, then these will probably pollinate your trees. Otherwise you will need to purchase two compatible varieties. The website section on varieties provides information on which varieties best go together.
The male flowers, called catkins
The red tufts are the female flowers
An introduction to traditional pruning
You do not need to prune a cobnut tree to make it produce nuts. However, if you never prune it, the tree will probably grow to more than 7m (20ft) tall. You will not be able to reach the nuts while they are in their 'green' succulent stage and will need to wait until they are ripe and ready to fall from the tree. The traditional method of pruning cobnut trees involves checking the height of the tree to within the reach of a picker, about 2m (7ft). The branches are thinned out and trained outwards to make a bowl-shaped tree on a short trunk.
Pruning normally takes place in winter and early spring, say from mid-November to mid-April. Firstly remove dead, diseased and broken wood. The tree must then be pruned so that it is sufficiently open to encourage the production of flowers and allow access for picking. Each tree should have 6-8 framework branches growing outwards. If there are too many, those which are too close should be thinned out to allow space for the others. If there are too few, gaps should be filled, perhaps using suckers. Any unwanted suckers should be removed at the base. Strong shoots will need to be removed from the tree to reduce height and density of growth, and some inwardly-growing shoots may need to be cut out to ensure the centre of the tree is not too dense.
Our Pruning Booklet provides more detailed information and can be downloaded from the Publications section; price £5.00. It includes information on establishing new cobnut trees and restoring trees which have become overgrown.
Where to get your cobnut plants
Do not plant a cobnut to generate your cobnut tree. Cobnuts do not come true from seed any more than a pip from a Bramley apple will grow into a tree producing true Bramley apples. You will get hazel nuts, but they may be small and thick-shelled and they may taste bitter. Purchase your tree varieties from a reliable nursery.
A few cobnut varieties
Kentish Cob is a reliable cropper, relatively hardy, with excellent flavour. It is recommended for domestic use. It is pollinated by Gunslebert, Cosford and Merveille de Bollwiller, and probably also by wild hazels.
Merveille de Bollwiller (also called Hall's Giant) is a hardy, vigorous and productive variety with large nuts. It is pollinated by Kentish Cob, Cosford, Butler and Ennis.
Butler is a large mid- to late-season nut. It is hardy, vigorous and a heavy cropper, and a short-husked variety which de-husks freely when ripe. It is popular for modern commercial production, and is pollinated by Ennis and Merveille de Bollwiller.
Ennis is a very attractive large round nut with a superb flavour, but a tendency to produce a significant proportion of blank nuts. It is pollinated by Butler and Merveille de Bollwiller.
Purple Filbert (also misnamed Red Filbert) is an ornamental variety with red or purple leaves. It produces a small crop of thin-shelled nuts of excellent flavour but which are particularly susceptible to nut weevil. It is not recommended for nut production.
Pests and diseases
Apart from grey squirrels, pests and diseases are not usually a serious problem except in commercial cobnut plats.
Grey squirrels are voracious feeders on nuts. A few trees can be denuded of cobnuts in a few days, or even hours, especially at the start of the season. Squirrels cannot usually take the entire crop from several acres, but can still cause considerable damage.
Nut weevil is a significant pest which both reduces yield considerably and adds to sorting costs. Adult insects deposit eggs in young nuts. The larvae which hatch from the eggs devour the developing kernel. They then gnaw a neat round hole in the shell to emerge a week or two after the start of the season. However, not all nuts will be affected, and those affected by weevil can be detected by the hole in the shell.
Bigbud is caused by a tiny mite that lives in the buds, and is most evident in early spring, when the enlarged buds which give the pest its name are conspicuous. Most infected buds fail to develop and drop off. Most nut plantations suffer from bigbud to some extent, but it is normally only a serious pest in commercial plantations.
Further information is available in our booklet 'Pruning Kentish Cobnuts'.