Walnuts are both domestic and foreign. Most familiar in the marketplace—and certainly-most important to the home gardener—is the so-called English or Persian walnut ( Juglans regia), which hails from southeastern Europe and southwestern Asia. The nuts are large, flavorful, and enclosed in relatively thin shells.
The black walnut (J. nigra) from the eastern United States is famous for its fine-tasting nut encased in a shell of rocklike hardness. Another eastern tree with a similar reputation is the butternut (J. cinerea). The western states have one important native, J. hindsii, the California black walnut; it is valued more as a rootstock on which to graft English walnut cultivars than for its nuts.
English walnuts are fast-growing, heavy-textured trees. The limb structure is thick and sturdy, and mature height may reach 60 feet with a spread to match. These walnuts will grow over quite a climatic range, but the key to a successful crop is proper cultivar selection.
Where winter lows are normally -20° to -30° F, plant only those designated as Carpathian walnuts. These are frequently seedling-grown trees (rather than individual varieties), the original stock of which stems from the Carpathian Mountains of eastern Europe. If late spring frosts are a feature of your area, choose cultivars that leaf out and shed their pollen late. And if your winters are fairly-mild, select one of the cultivars that needs little winter chill. Where summers are hot and humid, the pecan will be a better nut tree to plant because it is not nearly as disease prone as the walnut under those conditions.
Some walnut varieties are self-fruitful, and some need pollinators—an important distinction if you have room for only one tree. If you are allergy prone, take note that walnut pollen is a well-known allergen.
Good soil for English walnuts is fairly deep and definitely well-drained. The trees need regular deep watering for production of top-quality nuts (trees are actually somewhat drought tolerant) but cannot tolerate moist soil continually at the trunk base. Countless old orchard trees have succumbed to crown rot when the orchard has been converted to a subdivision and the trees subjected to lawn watering.
If a walnut and garden must coexist, it's better to have the tree at the garden margin where routine watering won't reach the trunk. The best watering method for walnuts is basin irrigation beneath the tree's canopy. Form an inner earth ring about a foot out from the trunk so the trunk will remain dry during waterings.
Young trees may begin bearing at 5 years and have a life expectancy of around 100 years. Planted in good soil, young trees should need no fertilizer. Established bearing trees may be helped by an annual fertilizer application just before they break dormancy.
Harvest time begins when husks start to split and release the enclosed nuts; this usually occurs in late summer or early autumn. At that time knock all the nuts out of the trees (if you wait for natural fall, squirrels may beat you to much of the crop), remove the husks, spread the nuts in a single layer, and dry for several days.
Codling moth can damage the nut crop in all walnut-growing areas; the walnut husk fly also zeros in on the developing nuts but is more prevalent in the west. Aphids and spider mites are two pests that favor walnut leaves, as does the fungus anthracnose; oystershell scale may affect twigs and small branches.
English Walnut Varieties for Midwestern and Eastern States
Adams', 'Broadview', 'Colby', and 'Mesa' are hardy named cultivars of Carpathian stock that do well in the coldest regions where walnuts can be grown.
Among standard (non-Car-pathian) English walnuts, the following cultivars have proven their worth. 'Hansen' This small tree leafs out in midseason and produces thin-shelled nuts. Widely adapted. Origin: Ohio. 'McKinster' Fairly late to leaf out, this variety is a favorite in Ohio and Michigan. Origin: Ohio.
Black Walnut Varieties
'Stabler' This variety produces a nut that is fairly easy to crack for a black walnut. Origin: Maryland. 'Thomas' This is the most popular and widely available walnut. The large nuts have excellent flavor. Origin: Pennsylvania.
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