Irish Nut Growers Association

promoting nut growing in Ireland

 

 

 
 

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Nut Cultivation

 

Choice of Species

  Soil pH Deep Soil Waterlogging Frost Pockets Shelter Space per tree Trees per hectare * First crops
Cobnuts 5.5-7.5 Advisable Some Tolerance Avoid Advisable 20-25m² 400-500 3-4 yrs
Chestnuts 5.0-6.5 Essential Slight Tolerance Avoid Advisable 80-150m² 65-120 4-6 yrs
Walnuts 5.5-7.5 Essential No Tolerance Avoid Essential 80-150m² 65-120 5-7yrs
Heartnuts 5.5-7.0 Essential No Tolerance Avoid Essential 80-150m² 65-120 5-7yrs

*per hectare of open space

 

Choice of Site

All nut trees do better on fertile soils. They can handle stony/gravely soils provided large holes are excavated for each tree and the material replaced with good soil, high in organic content.

Waterlogged sites are not suitable. Sites that are exposed to strong winds will only be suitable if additional shelter can be provided (for example, by planting shelterbelts or tall thick hedges).

Level sites

Level sites can be good, provided there is good drainage and the land isn't a frost pocket.

Sloping sites

All other things being equal, sites with southerly or southeasterly aspects will give the best results. The land warms quickly in the spring and generally speaking temperatures are a little higher during the growing and ripening season.

Sites with easterly and northeasterly aspects are colder but generally offer good wind protection.

Sites with northerly aspects are cold but often quite sheltered, and may still be suitable for cobnuts

Southwesterly and westerly aspects often are more exposed to prevailing winds and need to be assessed carefully before committing to planting.

Northwesterly aspects can be cold as well as exposed to prevailing winds and are the least suitable for nut growing.

 

Rainfall and other climatic factors

Cobnuts are quite tolerant of high rainfall and can succeed in most parts of Ireland providing the other requirements listed above are met. Rainfall limit 1600-2000mm

Chestnuts are more prone to disease in high rainfall areas. Also, heavy precipitation at flowering time can lead to poor pollination. High rainfall areas are often cooler, leading to poorer opportunities for nut ripening. Rainfall limit 1000-1200mm

Walnuts are prone to disease in high rainfall areas. High rainfall may also prevent proper ripening of nuts. Rainfall limit 1000-1200mm

Heartnuts may have greater tolerance of high rainfall than walnuts, but this remains somewhat speculative. Advisable limit 1000-1400mm.

On well ventilated sites with good drainage, nut trees may be successful in locations with higher levels of precipitation than indicated above.

Climate information

Information on rainfall, temperature and other climate indicators can be found here: Climate Data

The most suitable locations for nut growing mostly lie east of a line from Belfast to Galway to Shannon to Bandon (see 75mm contour on the rainfall maps for April and July - The optimum locations are better depicted by the 75mm contour on the rainfall map for September. The sunshine maps for the months June to October are also good indicators).

Walnut Map

A map depicting climate zones suitable for walnut-growing in Ireland can be found here: Walnut Map

A similar map depicting climate zones suitable for walnut-growing in the UK can be found here: Walnut Map UK

Shelter

Shelter is beneficial to nut trees in a number of ways. It protect flowers and leaves from desiccation or more severe physical damage, and prevents pollen from being blown out of the orchard. When winds are very extreme, shelter may protect branches from being broken. A sheltered orchard is one more friendly to small insects, which can assist with pollination. As air in sheltered orchards is much less mobile than the air in exposed ones, convection heat losses are reduced. As a result sheltered orchards tend to be much warmer on any day in which there is potential for heat gain from the sun. Shelter can take the form of topographical features such as hills, buildings or walls, hedges, or deeper shelterbelts. Solid barriers that rise vertically from the ground, for example buildings or stone walls, stop the wind dead in its tracks and generally cause turbulence. Such barriers are not especially beneficial for providing protection from the wind.

Barriers like hedges and shelterbelts that allow a proportion of the wind to pass through are generally best. Any wind that passes through the shelter trees is slowed by friction and loses a significant proportion of its velocity. The remainder of the wind is deflected over the top of the shelter barrier and over anything behind the shelter for a considerable distance. Inside the shelterbelt, the reduction in wind speed can be anything up to 50 percent. The reduction effect is strongest at a distance from the shelter of 4-7 times the height of the shelter (for example, if the shelter is 5m high, the biggest reduction in wind speed takes place at distance of approximately 20-35m from the shelter).

At greater distances from the shelter, the shelter effect gradually diminishes. At a distance of 15 times the height of the shelter, the reduction in wind speed is around 20 percent. This may not sound like much but as the power of the wind is proportional to the cube of its velocity, a 20 percent reduction in wind speed equates to a 50 percent reduction in wind power. At distances greater than 17-18 times the height of the shelter, the reduction in wind speed becomes insignificant. The rule of thumb for estimating the height of the shelter is not the uppermost twig (which will have zero effect on wind speed), but the highest part of the vegetation that is dense enough to blocks out the view.

Generally speaking, the deeper the shelterbelt, the greater the reduction in wind speed. Ideally, shelterbelts should be tapered to meet the wind: the outer part of the shelterbelt should be composed of shrubs (for example dwarf willow or gorse), while the tallest trees should be towards the inside. This tapered effect can be seen in the native tree and shrub vegetation on some of the islands in Clew Bay (Mayo), where the tallest trees are nearly always those further from the prevailing winds. Some shelterbelts have another line of smaller shrubs on the inside, though the benefit of these is somewhat marginal. Deciduous trees and shrubs are the best for shelterbelts. Although the shelter effect is much reduced when they lose their leaves in the fall, wind can be beneficical during the winter months.

Wind blowing through an orchard in winter reduces humidity and helps provide less favourable conditions for fungal and bacterial diseases. Too much shelter, such as that provided by heavy screens of conifers or tall trees of any type, is almost as bad as too little: the air behind the shelter becomes stagnant and an ideal place for diseases to flourish. Shelter that is too high also blocks out a lot of light, reducing the photosynthesis potential of the trees underneath.

 

Other Considerations

Forest Gardening

Attempting to grow nuts in a forest garden situation is not recommended. For more info click here

Planting in Hedging

Generally speaking, nut trees crop poorly when planted in hedges. Where no other space is available, cobnuts can be planted as a hedge in a single row at 1.5-2.5m spacing.

Seed-Grown Trees

Seed-grown nut trees will almost never come true to form, and may not produce viable nuts or only do so after many years. The only exceptions to this are pinenuts, Monkey Puzzle trees and edible acorns.

All cobnuts, chestnuts, almonds and the various cultivars of juglans and carya (walnuts, heartnuts, hickory, pecans and related species) propagated by seed will tend to revert towards the wild genotype, though occasionally some new characteristics will emerge. Seed-grown trees also take many years to reach nut bearing capability wheres trees propagated by grafting or stooling not only come true to form but begin nut production at a relatively young age. If you want nuts, don't waste time and resources on seed-grown trees.

 

Choice of Varieties

Given the pioneering nature of nut-growing in Ireland, it is impossible to say with certainly which varieties will perform the best.

For any given species of nut, it is recomended that orchards are planted with a selection of different varieties. This will increase the likelihood of good pollination as well as compensate for variations in yields between different varieties in any given year.

For more information please refer to the Species and Varieties page

 

Choosing trees

Bareroted versus container-grown

Container-grown trees can be planted out over a longer season as the roots are less vulnerable to drying out. As there is more work and other costs involved for the nursery that raises them, they are usually more expensive than barerooted trees.

However, many container-grown trees are grown in pots that are too small, resulting in congested roots that can take a number of years to recover. They can end up requiring more attention than barerooted trees, which rather negates any possible advantages.

Barerooted trees have to be planted during the dormant season, which runs approximately from December to April. No nut tree is completely dormant during this time, in fact the cobnuts flower during this period. However, it is best to plant barerooted trees before they come fully into leaf.

Barerooted trees vary a lot in size, age and quality. Generally you get what you pay for. The smaller/younger trees need a lot of nurturing for the first few years. They do not compete well with weeds and if neglected will probably fail. In the case of very small trees (under 80cm), it is nearly always better to grow on for one to two years in a well tended lining-out bed, before planting out in a final position.

Conversely, freshly-planted large trees are easily rocked loose by wind and must be secured to heavy stakes for at least the first few years.

 

General Tree Care

Cobnuts

Cobnuts are propagated by stooling. They develop new roots quite quickly and even one year trees can sometimes be quite strong. However it is better to choose robust two year or three year trees for planting out. Young trees that are being grown on for a few years before being planted out should be lifted and replanted each year during the dormant season so that roots can be trimmed back into a compact shape.

Cobnuts have a tendency to grow as multi-stemmed trees. In most cases they are best cut back to a single-stemmed tree and grown similarly to a bush-trained apple tree. Pruning is straightforward: remove any new shoots that emerge at ground level or from the lower part of the trunk, thin out congested or damaged branches, cut back the previous years growth to a strong bud at about half length. Aim to have about ten to twelve main branches.

Cobnuts can recover from serious damage. Even if the main trunk is severely injured the tree can be saved. Simply cut off the trunk low to the ground and train a new leader from the cluster of new shoots that emerge.

Staking is only required if the trees are over 1.6 m tall at the time of planting. The stakes can be removed after 1-2 years.

 

Chestnuts

Chestnuts are propagated by two different methods: grafting and stooling. Some of the hybrid varieties grow well on their own roots, and consequently can be propagated by stooling. Most varieties, however are propagated by grafting, with the scions grafted onto rootstock raised from Castanea sativa or Castanea sativa x crenata seed. The latter rootstocks are preferable as they are more disease-resistant.

Two to three year old trees are generally the best choice. If the trees are the grafted type, the graft should be well healed with no lesions or exposed wood. If the trees are purchased small and then grown on, they should be lifted each year as for cobnuts, and the roots pruned back.

The trees should be trained as half standards with an open-bowl shape thereafter. Apart from thinning out congested or damaged branches, and a little bit of shaping, not much pruning is required. The centre of the tree should be kept open.

Staking is only required if the trees are over 1.6 m tall at the time of planting. The stakes can be removed after 1-2 years.

 

Walnuts

The nut-producing varieties of walnut are always propagated by grafting. The grafting procedure is different from most other trees in that it has to be carried out at warm temperatures but also when the tree is dormant. This requires specially heated rooms or heated grafting tubes where the temperature is carefully controlled.

As with chestnuts and cobnuts, two or three year old trees are generally the best choice. In damp climates walnut trees are quite prone to cankers: open lesions where the bark has peeled back. In the case of a healthy tree with good roots, the cankers may eventually heal themselves. However, cankers on young trees do not always heal but sometimes get worse, and may eventually kill the tree. If the canker is on a branch or high on the main stem, the tree can be cut back to below that point. If the canker is low down, there is not much that can be done except keep vegetation away from the tree in order that the trunk may have a chance to dry out.

Avoid buying trees with cankers or with grafts that have not healed well.

Very small trees are best grown on for a year or two before planting out. The walnut tree sends down a very strong taproot - when lifting the tree take care that this root and other big roots are not damaged. Any damaged roots should be cut back to good material.

Pruning is similar to chestnuts but is best carried out during mid-summer, when the tree will heal itself the fastest. Pruning done in spring often results in the tree bleeding, which dehabilitates the tree and may increase risk of disease. Minor pruning can be carried out during winter. Cuts should be sealed with a proprietary pruning compound.

It is particularly important to keep vegetation away from the trunk of walnut trees.

Trees are best staked for the first couple of years. However, tree ties can cause cankers, so are best moved to a new location on the trunk at regular intervals.

 

Heartnuts

Heartnuts are closely related to walnuts. Most of the advice re walnuts applies to heartnuts too. Heartnuts appear a little more resistant to cankers and to some of the other diseases that can effect walnuts.