Growing English Walnuts

English walnuts (EW) are not as well adapted to the soils and climate of NYS as their cousin the black walnut (BW.)  EW generally flower earlier than BW and their flowers are frost sensitive, thus pollination and survival of the fertilized embryo are less certain.  EW tree health and nut production is best in hardiness zones 6 and 7, and more problematic in hardiness zones 5 or colder.  EWs are susceptible to walnut blight a bacterial disease which is more of a problem on sites with poor air movement and when trees are not pruned to increase light penetration and air circulation inside the tree canopy.  English walnuts are most often grown on EW and BW rootstock, and potentially on Manchurian walnut; at this point we don’t know if one rootstock is better than another and finding this out will require further study.  In an orchard setting EW trees should be planted on a 40 to 50-foot spacing.  They can get as large or larger than a full sized apple tree on its own roots, but can be pruned to maintain a smaller sized tree.  At a 40 to 50-foot spacing branches from one tree won’t touch those of a neighboring tree so that squirrel guards can be used to keep squirrels from climbing individual trees and jumping from one to another.  To save space when planting evaluation trials a 15 to 20-foot grid spacing may be more appropriate.     

Probably the best presently known cultivars for nut production (all available from Grimo Nut Nursery in Ontario, Canada) are:  Ames, Bauer, Broadview, Combe, North Platte and Young’s B1.  Broadview starts pollen production earlier than the other varieties mentioned; match with the others for better male/female pollen production and receptivity.  Ames was tested at a zone 5a hardiness site and North Platte comes from a zone 5a location so they may hold the best promise at present for those located in hardiness zone 5.  We have heard of EW growing and producing in hardiness zone 4 locations, though production is sporadic due to cold weather extremes. 

Site selection is critical for the success of English walnut plantings.  Select gently sloping land as this helps ensure improved cold air drainage (less likelihood of frost damage to flowers.)  Northeast slope aspects are best to delay spring flowering.  Walnuts prefer deep, well-drained loams with a soil pH of 6 to 7.  Avoid heavy clay loams and soils with a pH below 6 if possible.  At windy locations and on west facing slopes a porous windbreak to the west may foster proper pollination; avoid solid windbreaks as air movement is necessary to reduce the incidence of walnut blight infection (high humidity fosters the spread of infection.)  If possible lay out tree rows, roads, etc. on a 1 percent slope so that water moves from areas where it is needed least (concave/valleys) to where it is needed most (convex/ridges.)  This slows water movement across the landscape, increases infiltration/water capture, and reduces soil erosion. 

Take a soil sample to determine the soil pH and lime requirement.  Try to adjust the soil pH at least one year before planting (more is better); surface lime application followed by incorporation through tillage is the fastest way to raise pH throughout the soil profile, if this isn’t possible surface apply the lime using no more than 3 tons per acre (43,560 square feet.)  A rule-of-thumb is that surface applied limestone moves down into the soil profile at about ½-inch per year.  Pay attention to soil test calcium and magnesium levels and if lime is required to raise the soil pH use a high calcium content limestone on soils where there is a greater need for calcium and a high magnesium containing limestone (dolomitic) on soils having a greater deficiency of magnesium.  

English walnuts are very sensitive to competition with grass.  Kill any grass growing near where you are going to plant a tree and maintain a grass-free zone around the tree for at least 3 years.  Perennial grasses can be weakened by using repeated light tillage and planting smother crops like buckwheat or sorghum-sudangrass a year ahead of planting your tree crop.  That said, soil health experts have found that using the least amount of tillage necessary, or better still no-tillage is the best way to protect soil health and soil structure which is important for aeration and water infiltration.  Another control method is to cover planting locations with a 4 to 6-foot square piece of cardboard or other opaque material to shade out grasses the fall before planting.    A combination of cardboard and woodchip mulch can be an effective weed control measure.  We suggest that fields be limed to adjust the soil pH to 6.5 based on soil test results prior to planting.  If this isn’t possible, plant the tree and apply the required amount of lime around the tree prior to installing cardboard/woodchips; the cardboard needs to be tight against the soil surface, and neither the cardboard nor woodchips should touch the bark of the tree.  Take a soil test periodically within the drip zone of the tree to monitor soil pH and apply additional lime as necessary.  There are a number of OMRI approved herbicides now coming on the market though at this point we have little experience with them so use is strictly on a trial basis.  No added nitrogen should be applied to grafted walnuts during their first 2 to 3 years of growth as it may inhibit hardening off going into winter.  EW tend to increase in winter hardiness with age.  A light application of manure when grasses begin to green up in early spring coupled with an orchard understory of nitrogen-fixing white clover will go a long way towards supplying the nitrogen requirements of growing trees.  Further nitrogen rate adjustments can be made using leaf tissue analysis to determine if sufficiency levels have been met.

When planting EWs the planting hole should be wider than deep.  Don’t bend roots – dig further or trench so you can straighten a root out or clip it off to fit the hole.  Place the tree with the TOP MOST ROOT at or slightly higher than the finished landscape (bring the soil towards the tree and be sure all roots are covered.)  It is better to plant too shallow rather than too deep.  The best time to inoculate trees with beneficial mycorrhizal fungi is at planting time; either soak the roots in a suspension of mycorrhizal fungi or add an appropriate granular product throughout the planting hole.  No further soil amendments are necessary at planting, especially nitrogen which can keep newly grafted EW trees from properly hardening off going into winter.  Water weekly for the first growing season; at a minimum during the first month after planting and then during any dry spells occurring in the first growing season.  Watering during the early years can increase tree growth and may reduce the time it takes for nut production to begin.  In addition to the macro-nutrients, numerous micro-nutrients are necessary for tree health and vigor, especially boron and zinc.  So when studying your soil test results or better still when determined by leaf analysis pay attention to the levels of these two elements and if deficient formulate a plan for increasing plant uptake through soil and/or foliar applications.

EW trees should be trained to a central leader with the branches spiraling around the trunk if you were able to look down on the tree from the top.  Branches should be spaced on the trunk roughly 18 to 24-inches apart vertically and none should be opposite of another when looking at the tree trunk.  Pruning should be done in late February to early March, but before the tree breaks dormancy.  It is normal for walnuts to bleed (exude sap) after pruning, however, we don’t believe this hurts the tree.  Dead branches and vertical sprouts can be removed in late July to early August if weather conditions are dry.  When pruning the goal is to remove dead shoots,  retain limbs with strong branch angles (no more than 45 degrees, though less is better,) and open up the interior of the tree so that all leaves are exposed to as much sunlight as possible and to promote adequate air circulation which helps with disease prevention.  EW trees are prone to southwest bark injury (sap rises in the trunk on warm, sunny winter days and then is frozen at night splitting the trunk); painting the tree trunk with a mixture that is one half water and one half, interior, white latex paint can help to reduce the incidence of occurrence.

EW nuts will fall on the ground when they are mature.  The orchard understory, especially as you get closer to the trees should be composed of short growing perennials such as Dutch white clover so that mice, chipmunks and squirrels have the least amount of cover to hide in as is reasonable possible, while still providing soil protection and supplying liquid carbon to the beneficial microbes in the rhizosphere.  As harvest approaches vegetation in the orchard should be mowed close, again to reduce rodent cover and to make finding and picking up nuts easier.  Nuts should be picked up as soon as possible and dried for several weeks in a location with good air circulation to obtain the best flavor possible, as this helps to remove any lingering bitter aftertaste.  Many folks like to roast nuts to improve the flavor even more.  Try roasting cleaned nutmeats for roughly 10 minutes at 225 degrees F and be sure to check them often so that you don’t burn them.  Another post-shelling processing approach to try is to soak them in water for 6 hours and then dehydrate them for 10 hours at 105 degrees F. 


Ripening English Walnut

 

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