Detailed Explanation of Walnut Planting Techniques and Key Points of Cultivation Management

When cultivating walnuts, they bear fruit in 2 years, come into production in 3--5 years, and can enter the full bearing period in 6--7 years. After entering the full bearing period, the nut yield per mu can reach 500-800 jin. Let us take a look below at the planting techniques for walnuts.

Orchard establishment and planting

1. Site selection. Walnuts do not have strict requirements for environmental conditions; as long as the annual average temperature is above 9-16 degrees C and the annual rainfall is above 800 mm, they can be planted. Walnuts have relatively wide adaptability to soil, but because they are deep-rooted fruit trees and have relatively weak resistance, it is more suitable to choose deep, fertile loam with strong water retention. Walnuts are light-loving fruit trees and require sufficient light, so when establishing an orchard in mountainous areas, south-facing slopes should be chosen.

2. Planting. In order to bear fruit earlier and increase yield per unit area, dwarf and close planting should be promoted, and grafted seedlings should be used to achieve early high yield. Grafted seedlings can bear fruit 2-3 years after planting and enter the high-yield period in 4-5 years, while seedling trees need 8-10 years to bear fruit and 15 years to enter the high-yield period. At present, close-planting orchards are preferably spaced at 3×5 or 4×5 (45 plants per mu). Walnuts are monoecious fruit trees with separate male and female flowers, and the female and male flowers on the same plant generally do not bloom at the same time, so pollination between different plants is required. Therefore, only walnut orchards planted in blocks can obtain high yields. Walnuts are most suitably planted in autumn (September-November) or before bud break. Before planting, large holes can first be dug (80 cm in length, width, and depth), and organic fertilizer, phosphate fertilizer, and soil can be pressed in layer by layer, then the tree is planted on the hole, watered thoroughly to settle the roots, and the tree disk is covered with weeds to help survival. After planting, the trunk should be headed back in time to prevent drought and seedling death.

Soil management

1. Tillage. Deep plowing or pressing organic fertilizer into the walnut orchard is an effective measure for making young trees bear fruit earlier and for high yields in mature trees. Deep plowing can be carried out in spring, summer, and autumn. In spring, it is carried out before bud break; in summer and autumn, it is carried out after rain, combined with fertilization and burying weeds into the soil. Deep plowing should be carried out year by year outward from the planting hole, with a suitable depth of 60-80 cm.

2. Fertilization. Nitrogen and potassium are the main constituent elements of walnuts, and nitrogen is more than potassium. Increasing nitrogen fertilizer can significantly improve yield and quality. In phosphorus-deficient soil, phosphorus and calcium must also be supplemented, and organic fertilizer should also be added. Fertilization for young trees should follow the principle of light and frequent applications. From the year of planting to after germination, topdressing begins once a month, and one basal fertilizer application is made by the end of September. In years 2-4, fertilizer is applied 4 times each year in March, June, August, and October.

For mature trees (referring to grafted seedlings 4-5 years after planting), basal fertilizer is applied once a year and topdressing twice a year. Basal fertilizer is applied in autumn after fruit harvest combined with deep soil plowing (September-October), with 50 kg phosphate fertilizer, 100 kg plant ash, and 15 kg urea per mu. Topdressing is applied twice in total. The first topdressing is applied before bud break, with 20 kg urea. The second topdressing is applied at the hard-shell stage (June-July) to help increase fruit weight and promote flower bud differentiation, with 30 kg urea, 20 kg potassium sulfate, and 20 kg superphosphate. Farmers with the conditions can apply farmyard manure as well for better results.

Training and pruning

1. Pruning period. During dormancy, walnuts have a bleeding phenomenon, so pruning is not suitable; the best pruning period is autumn, which helps wounds heal earlier within the same year. Young trees without fruit can begin earlier from late August, while mature trees are best pruned around October after fruit harvest and before the leaves turn yellow.

2. Training of young trees. The shape is generally determined according to different planting densities and cultivar characteristics. For cultivars with high density or early-fruiting type and poor central leader, the open-center shape with 3--5 main branches is mostly used, and 4--6 lateral branches are selected and retained on each main branch. For cultivars with low density or late-fruiting type and strong central leader, the modified leader shape with 2--3 layers is mostly used, with 5--7 main branches per layer, and 3--4 lateral branches selected and retained on each main branch. Training should be done early rather than late, and generally should be completed within 5--7 years.

3. Pruning of fruiting trees. When walnuts enter the full fruiting period, the canopy is still continuing to expand, and fruiting sites are constantly increasing, so the contradiction between growth and fruiting is likely to appear. Therefore, in pruning, attention should always be paid to making good use of auxiliary branches and water sprouts, cultivating good branch groups, and promptly handling backward branches and drooping branches. From the early fruiting stage, strong fruiting branch groups should be cultivated in a planned way, continuously increasing fruiting sites and expanding the fruiting area. Prevent the inner canopy from becoming empty and the fruiting sites from moving outward. After entering the full fruiting period, the cultivation and rejuvenation of branch groups should be strengthened even more. Branch groups can be cultivated by using the pruning methods of “first release, then contraction” and “remove backward branches, retain slanted branches and back branches”. Water sprouts are generally not retained in the early fruiting stage to avoid disrupting tree shape, but in the full fruiting period they can be transformed into branch groups for use. Back branches should be controlled in time so as not to affect scaffold branches and fruiting mother branches. The main task of pruning trees in the full fruiting period is to timely adjust and balance tree vigor, regulate the contradiction between growth and fruiting, improve canopy ventilation and light conditions, renew and rejuvenate fruiting branch groups, and prolong the full fruiting period; the task of pruning aging trees is to adapt measures to the tree, heavily retract old and weak branches, and make full use of new shoots to renew and rejuvenate the canopy, and shape them early to prevent new shoots from becoming shaded and declining prematurely. At the same time, combine pruning with thorough removal of diseased and insect-damaged branches.

Arrangement of pollinizer trees

Walnuts belong to wind-pollinated tree species and are monoecious. However, in most cultivars the female and male flowers do not bloom at the same time. To improve fruit set rate and fruit quality, pollinizer trees must be arranged. The ratio of pollinizer trees to main cultivars is generally preferably 1:3—1:4, arranged evenly according to plant and row spacing.

Prevention and control of pests and diseases

1. Walnut canker. Methods such as removing diseased branches and fallen leaves, scraping off rough bark at the base of the trunk, and applying 5 degrees Be--10 degrees Be lime sulfur mixture or 50% thiophanate-methyl can be used for control, then spraying 50% Tuzet 800-fold solution twice in July--August can reduce the diseased plant rate to below 1%.

2. Walnut shoot borer. It mainly damages fruit. A comprehensive control plan should be adopted with cultivation and tillage under the trees and removal of residual branches and fallen leaves as the foundation, picking up black fruits as the main measure, and spraying the canopy as an emergency means. That is, after fruit harvest until mid-May of the following year, plow, expand the tree disk, and clean the orchard; from June--August, pick up black fruits and destroy them centrally; from early June to mid-July during the adult emergence period, in severely affected areas, spray the canopy with 50% fenitrothion 1000-fold--1500-fold solution or decis 3000-fold solution.

3. Batocera lineolata. It mainly causes damage by boring into the trunk. Manual capture of adults should be the main method, and medicine should be used in time to plug insect holes, crush eggs and larvae, and spray 40% insecticide 500-fold solution on the trees in August, with a control rate of over 90%.