Can Walnuts Be Grown in the South? Ripening Time and Key Cultivation Techniques
Walnut trees grow in most parts of our country, with more of them planted in the south, because walnut trees prefer a warm growing environment and are afraid of frost. They like fertile sandy soil with deep soil layers. They generally grow mostly in mountainous and hilly areas. So can walnuts be grown in the south? When do they ripen? What are the key cultivation techniques?
1. Can walnuts be grown in the south?
Walnut belongs to the tree species that prefer warmth. The suitable temperature range and frost-free period for its growth are: annual average temperature 9°C-16°C, extreme minimum temperature -25°C to -2°C, extreme maximum temperature below 38°C, and a frost period of less than 150 days. Judging from the adaptability range of walnut trees, planting walnut trees in the south is entirely possible. Walnut trees are deciduous trees, deep-rooted species, dicotyledonous plants, and highly adaptable, so when choosing to plant them, it is enough to select walnut seedling varieties with strong disease resistance.
2. When do southern walnuts ripen?
The ripening period of walnut fruit varies depending on the variety and climatic conditions. The ripening periods of early-maturing varieties and late-maturing varieties can differ by 10-25 days. Generally speaking, the ripening period in northern regions is mostly from early to mid-September, while southern regions are relatively earlier.
3. Key points of walnut cultivation techniques
Walnut belongs to deep-rooted tree species that prefer warmth and light and are afraid of wind. As the saying goes, “wind-sheltered walnuts fill the mountains like jujubes.” Walnut orchard sites should be selected in ecological areas that are flat in terrain, have deep soil layers, face the sun and are sheltered from the wind, have convenient transportation, pure water quality, and no pollution. The PH value should be between 6.05-7.05. Absolutely avoid choosing abandoned land, continuous cropping land, and saline-alkali land with a salt content above 0.25%.
1. Plant grafted seedlings
Generally, walnut seedlings propagated from seed begin to bear fruit in 6-8 years, and only enter the full fruit period after 20 years. Grafted seedlings, however, can generally bear fruit 3-4 years after grafting, producing benefits more than 3 years earlier than seedling-grown trees. Therefore, in order to shorten the juvenile period of walnuts, improve economic benefits, and increase fruit growers' income, early-fruiting grafted propagation seedlings should be selected.
2. Select excellent varieties
Be sure to choose excellent varieties that bear fruit early, have strong adaptability, a high kernel yield, thin shells, easy kernel removal, and high oil content. At present, the relatively excellent varieties include Luguang, Fenghui, Xiangling, Liaohe No. 1, Yuanfeng, Baojinxiang, Linhe No. 1 and No. 2, Xifu No. 2, Zhonglin No. 1, 8518, Xifu Lufeng, Jinbaoxiang No. 1, No. 2, No. 3, No. 4, etc.
3. Overcome the phenomenon of “dichogamy”
Walnut flowers are unisexual flowers and are monoecious. In some varieties, the female and male flowers do not bloom at the same time, which is called the phenomenon of “dichogamy” and affects the fruit-setting rate. Therefore, pollinator trees should be paired to achieve mutual pollination and fertilization and improve the fruit-setting rate. Generally, the planting ratio of the main variety to pollinator trees is 5-8:1. For example: Xiangling paired with Xilin No. 2; Xifu No. 2 paired with Luguang, etc.
4. Spring grafting requires “water drainage”
Compared with other fruit trees, walnuts have a lower grafting survival rate. The main reason: both the walnut rootstock and the scion contain tannins, which easily oxidize in the air to form a dark brown isolation layer, hindering the exchange of cellular materials between the scion and the rootstock. Spring grafting coincides with the late stage of walnut bleeding. Bleeding can inhibit the physiological activity of cells at the graft union and hinder the reduction of tannin oxidation condensation products. In order to improve the grafting survival rate, “water drainage” should be done below the graft union. Generally, for young trees, cut 2 incisions 10-20 cm below the union, 1-1.5 cm long, reaching the xylem. For large trees, generally cut 2-3 incisions below the union, with the same length and depth as above. In this way, the upward rise of bleeding can be cut off, improving the survival rate of spring branch grafting.
5. Pruning should avoid the bleeding period
From leaf fall to before bud break is the bleeding period for walnuts. If pruning is carried out, there will be many wounds and heavy bleeding, which not only makes the wounds difficult to heal, but also easily causes premature decline of tree vigor. Therefore, pruning should avoid the bleeding period. It should generally be carried out after the fruit is harvested in autumn and before leaf fall (Cold Dew), or after leaf expansion in spring until the young fruit expansion period.
6. Pay attention to cold protection for young trees
Young walnut trees have poor cold resistance and are easily frozen to death. Therefore, good overwintering cold protection work should be done. Cold protection methods include whitewashing, wrapping with plastic film, and burying in soil. Among them, burying in soil has a relatively good cold protection effect. The method is: generally after leaf fall and before the soil thaws, slowly bend the seedling down so that its top touches the ground, cover it with 30-40 cm of moist fine soil, and firm it down, then cover it with about 5 cm of dry fine soil. Before germination in the following spring, remove the soil and straighten the seedling trunk.
7. Correctly handle the “reverse pull” and head-stealing phenomenon of back branches
After walnut trees bear fruit, the upper branches on the main and lateral branches will weaken, and their back branches will quickly become vigorous, forming the phenomenon of “reverse pull” and head-stealing on the main and lateral branch heads. If not handled for a long time, they will extend for many years and become drooping branches, growing quickly and consuming much nutrition, causing the upper branches and rear branches of the original branch head to gradually dry up and die. Therefore, back branches should be handled correctly.
Handling methods: First, shorten-cut the drooping part at the branching point to raise the branch angle. Second, if the drooping angle is not large, the growth is moderate, and plump buds have already formed, they can be temporarily retained and cut off after fruiting. Third, if the drooping is severe and there is no fruiting capacity or very little fruit, they should be removed in time.