About The Walnuts

Some general information about the walnut trees planted

I have planted 26 different cultivars of walnut and heartnut. Although guided by the research from Martin Crawford and Andi Wilson I wanted to include as much variation as possible. There is so little research on walnut cultivar performance in the UK under organic cultivation methods I thought it was safer (from a disease and performance perspective) and more interesting (from a research perspective) to include as much genetic diversity as possible. I have trees originating mostly from Europe  (France, Netherlands, Czech Republic, Germany, Bulgaria, Austria and Italy) and some from USA and Canada. I have planted more of the trees, which I suspect will perform better (most of the French cultivars) and only a few of the other varieties to lessen the risk. I have two cultivars of walnuts that produce red nuts (Sychrov and Rote Danaunuss). I have a mixture of early season and late season nuts so can expect a harvest period from Mid-September to Late October. The trees were sourced from three suppliers. Most of the trees came from Fruit and Nut Ireland- these trees are three years old and bare-root. Some of the trees had quite substantial branched root systems, after having their tap root disturbed three times already from being moved around nursery systems. The remainder of the trees came from Martin Crawford (a mixture 2 year of bare-root and  one year 7 L container grown trees. The Czech cultivars came from Frank Matthews as one year grafts grown in 7 L containers. At the time of planting, I included all the different walnut cultivars I could find available for purchase in the UK. There are several other promising Romanian and European cultivars that I would have been interested in trialing but could not easily source. In the planting design the early season trees are on the lower part of the slope and the late season on the upper part of the slope. This is partly as the late season nuts will need more autumn warmth to help successfully ripen fruit, which they should gain on the upper part of the slope. Hopefully it will also make it easier to harvest the nuts in years to come if parts of the field can be harvested fairly sequentially.  The heartnuts are at the bottom to keep them separate from the walnuts and as they tend to ripen earlier. Due to the exposure from the South- West it is likely the trees on western edge will suffer more from wind damage. I have kept the cultivars together in rows for ease of management, but have tried to distribute the good pollinator species throughout the planting. 

Container grown vs bare-root

It will be interesting to see the difference in establishment between the trees grown in containers and those grown bare root in the nursery systems. The trees grown in the bare-root system have also been grown organically for the last two seasons, whilst the container stock from Frank Matthews has been reared chemically. Looking at the two different root systems ad contrasting them to the above ground growth, I feel the densely branched and haired trees from the organic system are better equipped to help the trees get established quickly and cope with stresses in the first season. Despite having been uplifted three times already and suffering some root damage they have a much greater root mass. Any damaged roots on the bare root trees I pruned off prior to planting and tried to avoid the long roots circulating within a planting hole- digging deeper instead so they could hang down to their full length. I have been taught it is better to prune a root back then plant it if it is damaged or coiled in a space. The trees from Frank Matthews despite being only one year old all had in excess of six-foot growth on them. The chemical liquid feed they received ensured rapid growth in year one- but now planted out in the ground I suspect they might get a shock when they have to fend for their own water and sustenance. As a result I pruned back the growth to 4ft on all these trees, with the hope the trees would be under less stress with less growth and few leaves to support initially. The container-grown trees were much easier to plant- but as a result will have very poor anchorage initially and I was glad to have substantial stakes to support them.

Walnut propagation: Budding and Grafting

As all the walnut trees I planted are named cultivars that means they have been clonally propagated from an originally tree. That means that all trees of a named variety are genetically identical to each other and from the original mother tree from which they came.  This is useful as it means their production and disease resistant traits are consistent, with variability due to soils and environment. However having large populations of genetically identical trees does leave your population vulnerable if a new disease or challenge should emerge as every member of the population has the same genetic vulnerabilities. From a production perspective it is much better however to take this risk, as seedling trees are unlikely to give as good a yields as parents and will not make a venture commercially viable. The way walnuts are clonally propagated is by grafting or budding- that is combining a a cutting from the cultivar you wish to propagate with a seedling rootstock. Unlike apple and other fruit trees there are no dwarfing rootstocks available for walnuts and the rootstock used tends to be random seedlings. Walnuts are challenging to graft compared to other tree species- partially as the wood has a hollow pith and wounds are slow to heal. When bench-grafting walnuts people use a hot grafting pipe- they place the graft union in an insulated pipe that keeps he wound around 27oC. The concept of the system is to allow healing of tissue around the graft union before the initiation of scion and/or root growth. The combination of this three way pull often leads to failure because of the stress it puts on the plant, but with using the hot pipe callusing system means that heat is only applied to the grafted area of the plant whilst the scion and rootstock remain cool. This prevents drying out and it delays growth. Bench-grafting is carried out in the dormant winter season, whilst budding is carried out in the summer. Budding involves inserting a bud into the bark and letting it heal over the winter. Next spring all the other growth is pruned back, to let the inserted bud become the new leader.

General information about growing walnut trees

Juglans regia is known by several common names including Persian walnut and English walnut. Walnuts are fast growing trees that can reach 18m wide and 30m high (although there is variation between cultivars). The trees need full sun, deep loamy soils and sheltered sites to grow and nut well. The trees come into leaf between Mid-April to Mid-May but flowers may open before. Walnuts are monoecious (so have separate male (catkins with pollen) and female flowers (that will develop into nuts post fertilisation) on the same plant- ‘one household’) and wind pollinated. Studies have demonstrated walnut trees can be pollinated by other trees over a mile away. shown in certain orchards that wind blown pollen came from trees over a mile away.

The release of pollen from male flowers may not overlap well with the time of female flower receptivity. This condition is referred to as dichogamy and some trees may be protandrous flowering (males earlier) whilst others protogynous flowering (females earlier). For successful pollination of an orchard cultivars should be selected that overlap the period of male pollen release and female reciprocity.

A tree grown from seed will start to produce fruit in 8 -12yrs, but grafted walnut cultivars will start to fruit in the fifth year.

Average Yields  (Martin Crawford, How to grow your own nuts)

	Yield per tree	Yield per acre 4050m2	Yield per Ha 10000m2
3-5 year	2-5kg	120-310 Ib	140-300kg
10-15 years	15-50kg	900-3000Ib	1-3.5 tonnes
Max Production	75kg	3000-4500 Ib	3.5-5 tonnes