Considerable research into nut production - particularly walnuts and chestnuts - has been carried out in Europe in the last two to three decades. During the 1980s and 90s, several research projects were undetaken in the Netherlands. Twenty-two named cultivars of walnut were trialled at the Research Centre for Fruit Growing at Wilhelminadorp in Zeeland from 1981 onwards. By far the best results were obtained with Broadview, a relatively compact variety from British Columbia in Canada. Annual precipitation at Wilhelminadorp is around 800mm.
Of the Western European countries, France has the best tradition of growing walnuts, with many distinct local varieties. Among the more adaptable cultivars is Ronde de Montignac from the west of the country. A walnut breeding programe in the 1970s and 1980s yielded three promising new cultivars: Ferjean, Fernor and Fernette. All three varieties begin cropping at a young age and form compact trees.
Trials in England
From an Irish perspective, some of the most interesting work has been undertaken by Agroforestry Research Trust at its site in Dartington in Devon, England. Here a number of named cultivars of chestnuts and walnuts have been grown since the mid 1990s. Dartington is situated midway between Dartmoor and the Devon resort of Torquay. The climate is mild and very comparable to the south west of Ireland. However, annual precipitation at Dartington is around 1100mm a year, which is higher than many parts of southern and eastern Ireland. Rainfall being a critical factor in the successful cultivation of both walnuts and chestnuts, it is reasonable to assume that varieties that do well in Dartington will also succeed in many parts of Ireland.
Research from the Agroforestry Research Trust shows a wide range of variation in susceptibility to disease. Interestingly, Broadview - the clear champion in the trials at Wilhelminadorf in the Netherlands - showed high susceptibility to walnut blight: a fungal disease causing die back and crop failure. However, Broadview was found to have good resistance to anthracnose - another fungal disease causing defoliation and premature nut fall.
Among the cultivars trialled by the Agroforestry Research Trust, Broadview, Fernette, Ferjean and Ronde de Montignac showed good resistance to anthracnose. Plovdivski, Fernor, Ferjean and Ronde de Montignac showed good resistance to walnut blight. The trees at Dartington began cropping after about 5 years. Cropping was thought to have been delayed owing to the exposure of the site, which caused male flowers to be blown off by winds. In later years the site was protected by a windbreak of Italian alder (Alnus cordata). Alder is also a soil nitrogen fixer.
In terms of yield, Corne du Perigord, Soleze, Ronde de Montignac, Frankette, Mayette, Fernor and Fernette have performed best. Chandler, Parisienne, Meylannaise and Broadview were next. Corne du Perigord produced 7kg per tree in 2006.
The results for chestnuts grown at Dartington were perhaps more impressive, with six varieties yielding over 20kg per tree per annum from 2004-2006 (9th-11th years after planting). The six varieties were Belle Epine, Bournette, Bouche de Bétizac, Marlhac, Marigoule and Vignois. Other varieties that performed well included Herria, Verdale and Rousse de Nay.
Ireland
Research into nut cultivation is also being carried out at one or two locations in Ireland. Paul McCormick and Jacinta French of Woodkerne nurseries have been propagating and growing nut trees on land just north of Skibbereen in Co. Cork. Although Skibbereen has a lovely mild Gulf Stream climate, it also experiences quite high precipitation - at least 1200mm a year. The work being carried out by Paul and Jacinta will be of great benefit in adding to the sum of knowledge of nut growing in Ireland.
As time goes on, we will also have data on how well nut trees are doing at our own nursery and elsewhere in our locality. The Westport area experiences over 1500mm of rain per annum and can be regarded as being at the outer edge of the normal tolerance range of both chestnuts and walnuts. However, we have discovered that old chestnut trees in the area produce viable nuts, even in a bad year like this one, and we do expect success with some of the varieties we are trialling in Mayo. Anything that produces nuts here can be expected to do very well further east or south.
Nuts and food security
Nut crops may have a significant role to play in future food security in Ireland. The critical paths are examined in this recent article:
Nut trials
Fruit and Nut is interested in supporting walnut and chestnut trials in Ireland. Such trials are important in order to establish which varieties do best in the Irish climate. As fruiting begins at a young age - often under 5 years - with many varieties, useful information will not be long in coming.
To facilitate trials, Fruit and Nut can supply quantities of walnut and chestnut trees at discounted prices, and will carry out a free site assessment beforehand. Further assistance with planting can be provided if required. Normally, the minimum quantity for a test project would be 20-30 trees. However smaller quantities may be considered in certain circumstances.
Trees are normally planted 8-12 meters apart, although distances of up to 30 meters may be considered if space permits. Greater distances may prevent successful pollination. Protection from livestock is essential. This can take the form of a stock proof fence round the whole plantation or individual fencing round each tree. The latter has the added advantage of allowing grazing between the trees. This keeps down the vegetation and makes better use of space.
Trees can be supplied from early December onwards. Please contact us for further information.
National Nut Audit
In Scotland in the 1870s and 1880s, two remarkable independent tree audits were carried by the Highland and Agricultural Society of Scotland. These audits catalogued the largest walnut and Spanish chestnut trees growing in Scotland at that time. Some of the trees were over 200 years old. What is especially interesting is that a number of the trees are recorded as producing ripe nuts on a regular basis, in defiance of Scotland’s northern latitude and cold climate.
No similar audit of nut trees has ever been carried out in Ireland. However, anecdotal evidence suggests nut trees were once common on many of the big estates and can still be found in a few places. Some of the surviving old trees, usually dating from the 18th or 19th Century, continue to produce nuts in spite of the limited opportunities for pollination.
One feature of all the oldest nut trees is that they would have been grown from seed: typically chance selections acquired from Spanish or French sources. Also, historically speaking walnut and chestnut trees were generally planted for their fine timber, not for their nuts. Any nuts that occurred were considered a bonus.
The science of nut growing has moved on considerably in the last one hundred years and has followed in the footsteps of earlier developments with fruit trees. It is now common practise to propagate nut trees using techniques such as grafting and layering. This guarantees that new trees will have the characteristics of the parent wood. Such characteristics include precociousness (the ability to begin fruiting at an early age), disease resistance, and of course cropping ability.
In order to get a clearer picture of the possible climatic limitations to nut growing in Ireland, it would be immensely useful to know the locations of trees are already successfully producing viable nuts. Given that new nut cultivars can probably produce nuts in a wider range of climatic conditions than older seed-grown trees, it is reasonable to assume that any part of Ireland where nuts are already known to ripen offers very good nut growing potential in the future. In addition, it is likely that the walnut and chestnut cultivars most suited to Irish conditions will produce viable nuts in many locations where nut production was not previously known or considered.
A national nut audit is now being undertaken by the Sustainability Institute. The data complied will be used to draw up a map depicting the approximate locations of nut-bearing trees. Further details of the trees and of the local micro-climate and soil conditions, if known, will be provided in a written report.
We would be very grateful if anyone with nut-bearing walnut or chestnut trees on their land, or who knows of nut-bearing trees in their locality, would get in touch with us.
Pollination and Disease Resistance
The nut varieties sold at Fruit and Nut are carefully selected for characteristics such as high disease resistance and early fruiting.
Cobnuts will grow almost anywhere and are worth a try on any ground that isn't waterlogged or very acidic. Walnuts and chestnuts are fussier but providing they are planted in well drained fertile ground, the varieties offered here can be expected to succeed in many parts of Ireland.
Successful pollination relies on a number of factors: compatible varieties, fine weather during flowering, availability of insects, and relatively short distances between individual trees. The weather we can do little about, apart from choosing good sites and providing shelter from prevailing winds.
Bees can be encouraged by planting late spring/early summer- flowering bee plants within the nut orchard.
The odds of successful pollination also increase with the greater number of different cultivars planted. If space permits, it is advisable to plant four or five different cultivars of a particular type of nut tree.
