| The Persian walnut, so named to indicate its place of origin, is the most popular walnut, grown in many parts of the world. It was used as a source of food on the ancient trade routes across Asia and so became established in China in the east and Europe in the west. From Europe, it spread westward to North and South America as well as Australia as the "New World" unfolded.
It is most commonly
called "English" walnut, but it is also known by other
names such as "Carpathian" walnut, and "California"
walnut. The Carpathian walnut was introduced to Ontario in the mid
30's by Rev. Paul Crath. Convinced that the Persian walnut from
the Carpathian Mountain region of his native Poland was hardy enough
for Ontario conditions, he returned to Poland on several occasions
and brought back several tons of "Carpathian" walnuts
which were widely distributed over eastern North America. These
trees have been successful as yard trees everywhere in zone six
in Ontario, but only moderately successful as commercial trees.
Persian walnut introductions from Germany and Southern Russia have also met with the same success, while the Persians grown in California have proven to be far less hardy and unsuited to our climate and shorter growing season.
Fresh Persian walnuts from Ontario are generally sweeter and better flavored than the counterpart from California and offshore. As a result local growers are able to sell all they produce, especially to people of European extraction who are familiar with the fresh quality of local produce.
The walnuts grown in Ontario can stand -30 C and colder during the middle of winter, but a cold spell of -20 C in March could cause serious dieback. Late spring frosts in April or early May of -3 C could cause tip dieback and seriously reduce the crop which forms inside the tip buds. For the serious grower, spring conditions causing tip dieback and the loss of crop can be controlled with wind machines and reverse a bud killing frost.
Persian walnuts are very susceptible to walnut blight, a bacterial disease, which attacks the flowers, twigs, leaves and more importantly, the nuts. The disease is most active in the spring on young tissues and by mid-summer, becomes nearly dormant as the tissues mature.
It needs water in the form of rain or heavy dew to spread to new areas of infection. It causes blackened lesions on the new growth. Flowers and nuts that are infected early in the season turn black and abort, while the nuts affected later carry the lesions to nut drop stage. The husks on infected nuts do not come loose and often the kernel is discolored or blackened too, making the nuts unusable.
Copper oxychloride spray is registered for control of this problem. This copper spray needs to cover the nuts thoroughly and must be present before rain to be effective. In a wet season, weekly sprays will be necessary from bloom to mid-summer in orchard situations. As the trees grow taller, a sprayer with a volute will be necessary to reach the tops of the trees. Home growers with a few trees may find the problem to be less serious and can live with the reduced crop in bad years.
Persian walnuts will grow in a range of well drained soils from sand to clay loam. The pH should be between 6 and 7. They grow to 15 m tall and spread about 10 to 15 m as they mature. Grafted trees will begin to bear in 3-4 years while seedling trees can take 5 years or more.
If seedling trees are used for orchard plantings, it is important to use seedlings from superior trees. Generally, improved parent seedlings will be more productive, reasonably thin shelled and good quality. Of course to be sure of quality, filling, and production, the grafted tree is the best choice.
Persian Walnuts Qualities
Nut & Kernel Quality:
The nut should be medium to large size and well-sealed. The meat should be well filled, without shrivel and with a light golden color. 50-55% nut meat is ideal. The shell should be easy to crack but harvested and handled without breaking too easily.
A good selection should be early ripening (mid- September to early October), and heavy annual bearing. Lateral bearing character would help to increase production.
Good selections need to be late enough leafing to avoid flower damaging frosts and survive exceptional winter conditions with minimal damage.
Walnut Blight resistance:
Cultivars or seedlings, even in blight prone years, that get much less blight damage on the nuts are preferred. This can be the difference between a good year and a bad one.
A prolonged dry spell can test walnut trees for endurance. A heavy crop and 2-3 months with little or no rain can cause severe stress on walnut trees that are not irrigated. Some trees will drop leaves mid-summer to compensate. These same trees often will finish the crop and have severe dieback the following spring, losing major limbs. Drought tolerant trees will hold the majority of the leaves and survive the winter unharmed.
Delayed Leaf Drop:
Some walnut trees drop most of their leaves before the nuts have all dropped. The leaf litter that covers the nuts can make the rest of the harvest difficult. The favoured trees are those that hold most of the leaves on the tree until the nuts are all down or until a severe frost hits.
Superior Persian Walnut Cultivars
Persian walnuts are partially self-pollinizing. To assure a full crop, two or more trees are needed. Some trees are protandrous, that is, they produce male catkins ahead of female bloom. Other trees are protogynous, meaning that female bloom occurs before the males catkins are shedding. Best pollinizing occurs when protandrous trees are matched with protogynous ones.
The list of Persian walnut selections is almost endless. Many are unsuited to Ontario or lack the above characteristics. The list below contains cultivars that are among the best for Ontario conditions.
is a hardy tree introduced from Utah. It is an annual, very productive tree with high walnut blight resistance and drought tolerance. The nut is medium size and oval with good cracking characteristics. It is protandrous so paired with 'Broadview' or 'Sejnovo' will provide best production. Suited for zones 6a-8, commercially 6b-8.
(originally 24-H-24) is from the Iowa State University field trials at Ames, Iowa introduced by Dr. Allan Beck. This selection has been performing well in Niagara. It is productive, hardy, drought tolerant and has good blight resistance. It is mid-season ripening and holds its leaves well until after harvest. The nut is oval, large size and easy cracking. It is protandrous so for best production, pair this one with 'Broadview' or 'Sejnovo'. Suited for climate zones 6a-8, commercially 6b-8.
Earl Young from Lyons, NY introduced this annually productive 'Broadview' seedling selection. The nut is very attractive, very well filled, large, and round in shape. The tree is healthy, hardy and vigorous growing. It has good walnut blight resistance and drought tolerance. It is mid-season ripening and holds its leaves well at harvest. Pair it with 'Broadview' or 'Sejnovo' for good production. Suited for climate zones 6a-8.
This cultivar was introduced from North Platte, Nebraska, a zone 5a area of relatively harsh dry climate conditions. It is a good producer of large size oval nuts that are easy cracking. It has good walnut blight resistance and is drought tolerant. It holds its leaves well until harvest is over. It is a protandrous cultivar and so it should be paired with 'Broadview' or 'Sejnovo' for best production. Suited for climate zones 6a-8.
was introduced by Jack Gellatly from Kelowna, BC. It is one of our hardiest selections. It is productive and has good blight resistance and drought tolerance. It is one of our latest to vegetate in the spring but one that will drop leaves earlier than most. The nut is large, oval and good cracking. It is a protogynous cultivar and is a main pollinizer for most of the above selections. Suited for climate zones 6a-8.
is a productive selection from Bulgaria for its walnut blight resistance. It is drought tolerant and holds its leaves until end of harvest. The nuts are large, oval and easy cracking. It is a protogynous cultivar and along with 'Broadview', is a main pollinizer for all of the other cultivars listed. Suited for climate zones 6b-8.
is a rare walnut cultivar introduced by Ken Dooley from Marion Indiana. Unlike most hybrids with eastern black walnut, it has a thin, paper shell that can be cracked with fingers. The tree is very productive, vigorous and leans toward the Persian walnut in most of its characteristics. It exhibits the best walnut blight resistance and is drought tolerant. It is early to mid-season ripening and holds its leaves until harvest is over. The nut is medium size, round and very well-filled. A small number of the nuts are not well sealed at the tip. It is a protandrous cultivar and so should be paired with 'Broadview' or 'Sejnovo' for best production. Suited for climate zones 6a-8.
This introduction from Pennsylvania is a very large oval nut, the size of a goose egg. Nuts of this size are usually considered a novelty, because the large size shell is often poorly filled. This selection fills better than most and has a fine sweet flavor even when taken fresh off the tree.
It is thin shelled and cracks easily. It is very productive but does have problems with walnut blight and nut fill in some years. It is a protandrous cultivar so it should be paired with 'Broadview' or 'Sejnovo' for best production. Suited for climate zones 6b-8.
For commercial orchards, tile drainage and irrigation are recommended to maintain good soil conditions for tree growth and harvesting.
It is difficult to recommend fertilizer requirements. A soil test should be used and the laboratory can suggest an appropriate fertilization. For small growers, a 15-15-15 mixture at .5 kg per 4 cm trunk diameter should be spread under the root area but away from the trunk in early May. One application should be adequate, but you may split the application in two with a mid-June treatment.
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