When Do Walnut Trees Bloom? Reasons for No Fruit and Methods for Early and High Yields
Walnut trees are also called Persian walnut, walnut, and black walnut. Varieties are divided into wild hickory and artificially grafted improved walnut varieties, and they are planted throughout China.So when do walnut trees usually bloom? What should you do if they bear no fruit? How can you promote early bearing and high yields in walnut trees?
When do walnut trees usually bloom?
1. After a walnut tree is transplanted, it needs a period of adaptation. In general, the growth cycle of a walnut tree follows a 3-year cycle: it blooms once every three years and bears fruit once every three years.
2. The flowering period of a walnut tree is generally about 20 days, and walnut trees bloom roughly from April to May.
3. Walnut is a green flowering plant. The male catkins hang down, about 5-10 cm long, rarely up to 15 cm. The bracts, bracteoles, and tepals of the male flowers are all covered with glandular hairs. There are 6-30 stamens, and the anthers are yellow and hairless. The female spike usually has 1-3 (or more) female flowers. The involucre of the female flower is covered with very short glandular hairs, and the stigma is purplish red.
What should you do if a walnut tree bears no fruit?
Reasons walnut trees bear no fruit:
1. Non-varietal cultivation: A walnut tree grown from seed is called a seedling tree, and no grafting of superior varieties has been carried out on the seedling tree. If the walnut seeds used are not selected, the resulting walnut trees vary greatly, with mixed quality; some bear fruit late, and only produce fruit about 10 years after planting.
2. Poor site conditions: If the planting site for walnut trees is poor, with a thin soil layer and infertile soil, and the trees are left to grow without management, this causes long-term nutrient deficiency in the tree, weak branches, no flower buds, and no fruit.
3. Improper management: First, too much nitrogen fertilizer is applied and there is no lack of water, causing excessive vegetative growth, with many dense branches, poor ventilation and light penetration, and no formation of the short and medium fruiting branches, so no fruit is produced. Second, for the sake of intercropping under the trees, the lower branches of the walnut canopy are all pruned away, so the whole canopy has too few branches and most are water sprouts; the tree posture is upright, with strong upper growth and weak lower growth, and fruiting branches cannot form either.
4. Poor pollination: Walnut is a wind-pollinated tree species. It is monoecious, but in most varieties the female and male flowering periods are not synchronized, and there is no other fruiting walnut orchard nearby, resulting in poor pollination and few fruits.
5. Severe pest and disease problems: Damage by pests and diseases affects the growth and fruiting of walnut trees. For example, the flower bud gall midge specifically feeds on the female flowers of hickory trees, so there is no basis left for fruiting.
What to do if there is no fruit:
I. Soil management
1. Tillage: Deep plowing in walnut orchards to bury green manure or incorporate organic fertilizer is an effective measure to make young trees bear fruit earlier and mature trees produce high yields. Deep plowing can be carried out in spring, summer, and autumn: in spring before budbreak, and in summer and autumn after rain, and weeds should be buried in the soil together with fertilization. Deep plowing should proceed outward year by year from the planting hole, with a depth of 60-80 cm being appropriate, but care must be taken to avoid damaging thick roots more than 1 cm in diameter. Young walnut trees grow relatively slowly, so leguminous crops or green manure can be intercropped between the rows. In mature orchards, herbicides are used 2-3 times each year from April to September to control weeds, and one intertillage is done in autumn and winter.
2. Fertilization: Nitrogen and potassium are the main constituent elements of walnut, and nitrogen is needed more than potassium. Increasing nitrogen fertilizer can significantly improve yield and quality. In soils lacking phosphorus and calcium, 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 until after budbreak, begin topdressing once a month until base fertilizer is applied at the end of September. In the second year, apply fertilizer 4 times per year in March, June, August, and October. For mature trees (referring to grafted seedlings 4-5 years after planting), apply base fertilizer once a year and topdress twice a year. Base fertilizer is applied in autumn after harvest together with deep plowing and green manure incorporation (September-October), with 5000 kg of organic fertilizer (decomposed chicken manure), 50 kg of phosphate fertilizer, 100 kg of plant ash, and 15 kg of urea per mu. Topdressing is applied twice in total. The first topdressing is applied before budbreak, with 1500 kg of organic fertilizer and 20 kg of urea per 667 sq m. The second topdressing is applied at the hard-shell stage (June-July) to help increase fruit weight and promote flower bud differentiation, with 2500 kg of organic fertilizer, 30 kg of urea, 20 kg of potassium sulfate, and 20 kg of superphosphate per mu.
3. Irrigation: Walnut likes moisture and tolerates waterlogging, but has weak drought resistance. Irrigation is an effective measure to increase yield. If the soil is dry and lacks water during the growing period, fruit set is low, the husk is thick, and the kernel develops poorly; if water is not supplied after fertilization, the fertilizer effect cannot be fully exerted either. Therefore, timely irrigation should be carried out at all stages such as flowering, rapid fruit enlargement, after fertilization, and during winter drought.
II. Training and pruning
1. Pruning time: During dormancy, walnut has a bleeding phenomenon, so pruning is not suitable then; the most suitable pruning time is autumn, which helps the wounds heal within the same year. Young trees without fruit can be pruned starting in late August, while mature trees are best pruned around October after harvest and before the leaves turn yellow.
2. Training young trees: Walnut has a strong trunk and especially obvious apical dominance of the buds. The terminal bud develops more plump and larger than the lateral buds, and the canopy shows obvious layering. In view of these characteristics, it is appropriate to use the modified leader system, and training is very easy. The training method is as follows: trunk height 50-80 cm (if the current-year seedling is not tall enough, training can wait until the sapling has grown for another year). In the year of planting, do no pruning at all; only straighten the trunk and protect the terminal bud (if the terminal bud is damaged, choose a strong bud to replace it). After budbreak in spring, the terminal bud grows upright and upward. Use it as the central leader. For the lateral branches sprouting below the terminal bud, in May-June select 3-4 well-distributed, vigorously growing lateral branches as the first layer of main branches, and remove all other new shoots. In the second year, cultivate the second layer of main branches in the same way, keeping 2-3 main branches in the second layer (60-80 cm from the first layer). In the third year, select the third layer of main branches, keeping 1-2 main branches, 570 cm from the second layer. From years 1-4, the main branches do not need pruning, and lateral branches can naturally form to expand the canopy. It generally takes shape in 3-4 years, and at that time the tree height is about 3-5 m.
3. Pruning fruiting trees: When walnut enters the full fruiting stage, the canopy is still continuing to expand and the fruiting sites are constantly increasing, so the contradiction between growth and fruiting readily appears. Ensuring high and stable yields in walnut is the main task of pruning in this period. Therefore, in pruning, attention should always be paid to cultivating good branch groups, making good use of auxiliary branches and water sprouts, and promptly handling backward branches and drooping branches. From the early fruiting stage onward, vigorous fruiting branch groups should be cultivated in a planned way, constantly increasing fruiting sites. Prevent the interior of the canopy from becoming hollow and the fruiting sites from moving outward. After entering the full fruiting stage, the cultivation and rejuvenation of branch groups should be strengthened even more. Branch groups can be cultivated by the pruning methods of “first release, then contraction” and “remove backward branches, keep slanting branches and back branches”. Water sprouts are generally not retained in the early fruiting stage, so as not to disturb the tree shape, and in the full fruiting stage they can be transformed into branch groups. Back branches should be controlled in time so as not to affect the scaffold branches and fruiting mother branches. Drooping branches are mostly not well developed, have poor fruiting capacity, and waste nutrients in vain, so they should be handled according to the specific situation.
III. Thinning male inflorescences
During the development of male and female flowers, a large amount of stored nutrients and water in the tree is consumed. Especially during the rapid growth of male inflorescences and the mass opening of female flowers, the amount of water in the tree often becomes a limiting factor for female flower growth and development. Thinning excessive male flowers can reduce the consumption of nutrients and water in the tree, so that more nutrients and water are supplied to female flower development, flowering, and fruit set, thereby increasing yield and quality, and also favoring new shoot growth and strengthening tree vigor. The earlier male flowers are thinned, the better, and the earlier the thinning, the greater the yield increase; the proportion of buds and female flower buds determines this. After thinning male flowers, a ratio of male flowers to female flowers of 3-60:1 is more appropriate. For plants with many mixed buds and few or very few male flower buds, male flowers should be thinned little or not at all. The method of thinning male flowers can be combined with pruning by using a wooden pole with a hook, pulling the branches down, and breaking them off by hand.
How can you promote early bearing and high yields in walnut trees?
1. Graft superior variety seedlings: Superior walnut varieties such as Xiangling and thin-shell bear fruit early, produce high yields early, and have excellent quality. They also have strong resistance. Uniformly planting grafted seedlings of superior varieties can achieve the goals of early fruiting, high yield, and uniform fruiting.
2. Artificial supplementary pollination: To overcome the problem that female and male flowers open at different times and thus affect pollination and fruit set, artificial supplementary pollination can increase the fruit set rate. The suitable pollination period is when the female flower stigma opens in an "inverted figure-eight" shape. At this time, newly opened male inflorescences can be collected from large fruiting trees and hung above the trees to be pollinated so that the pollen falls naturally. Alternatively, after collecting pollen, dilute it 3-5 times with talcum powder, put it into a three-layer gauze bag, and shake it artificially above the trees to be pollinated. Pollination is best done on a sunny morning from 9-10 o'clock.
3. Meticulous management: Fertilize and water. For vigorous trees, increase phosphorus and potassium fertilizer, control the amount of nitrogen fertilizer and irrigation, apply base fertilizer early, and combine deep digging to cut roots, promoting the tree vigor to change from vigorous to strong. For weak trees, apply more organic fertilizer, more ground topdressing and foliar spraying, strengthen vegetative growth, and restore tree vigor. The main insect pests of walnut include the walnut fruit moth, which damages the fruit, and the cloud-banded longhorn beetle, which damages branches and trunks; the main diseases include walnut canker. Pests and diseases should be controlled comprehensively, management should be strengthened to enhance tree vigor and disease resistance, and for chemical control, forecasting and monitoring of pests and diseases should be strengthened so that key pesticides are applied before pests and diseases cause disaster.