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" was 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 introductions from Germany and Southern Russia have also met with the same success, while the Persians grown in California have proven to be less hardy and unsuited to our climate and shorter 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. Due to the fickle nature of the tree, production can be variable.

20 year old Persian Walnut

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. Bordeau mixture or copper oxychloride spray is registered for control of this problem. These copper sprays need 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. 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. Generally, seedlings from good selections are productive, reasonably thin shelled and good quality, but to be sure of quality, filling, and production, the grafted tree is superior.

Persian walnuts are selected for:

1. Kernel Quality The nut should be medium to large size and well sealed.. It should be well filled, without shrivel and with a light golden color.
2. Production A good selection should be early ripening, heavy annual bearing, hardy and moderately resistant to walnut blight.

Persian Walnut Cultivars

The list of Persian walnut selections is almost endless. Many are unsuited to Ontario. The list below are among the best for Ontario conditions.

Lake - This cultivar has been grown in Southern Ontario successfully for more than 30 years. It is a large well sealed oval nut with a 50 % kernel by weight. It drops early and is moderately resistant to walnut blight. It is hardy and productive.

Metcalfe - Metcalfe originates in the Rochester area of New York. It is a round, medium sized, thin shelled nut with 55% kernel. It is productive and early ripening. It is moderately resistant to blight.

Coble 2 - 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. It is hardy for the Niagara area and Southwestern Ontario.

Persian walnuts are partially self pollinating. To assure a full crop, two or more trees are needed. For commercial orchards, tile drainage and irrigation may be needed. 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 in early May. One application should be adequate, but you may split the application in two with a mid June treatment.

Click here to view the Persian Walnut Planting Plan