Technical measures to promote fruit set in pomegranate cultivation

The flowers of the pomegranate are bisexual and, depending on the degree of pistil development, are divided into complete flowers and incomplete flowers. Complete flowers are gourd-shaped or tubular flowers, commonly known as “big-bottomed fruit flowers”, and are the main part that sets fruit; incomplete flowers have a trumpet-shaped calyx tube and are called “bell-shaped flowers” and “pointed-bottomed false flowers”, and cannot be fertilized or set fruit. Pomegranate trees often produce a very large number of flowers, but fruit set is low and yield is very poor, especially in orchards under extensive management. The main reason is that pomegranates have few complete flowers, generally accounting for only about 10% of the total flowers on the tree; the formation of degenerate flowers is mostly caused by poor nutrition during flower bud differentiation. Only complete flowers can set fruit, but even their fruit-setting rate is not necessarily high. Among the successive flushes of flowers, the first flush has a fruit-setting rate of 4.3%-6.1%, the second and third flushes 10.5%-53.7%, and the last flush 7.5%-33.3%. Therefore, the key to promoting fruit set and increasing yield lies in raising the proportion of normal flowers and their fruit-setting rate.

1 Improving the nutritional status of the tree

From July to October, spray the foliage with 0.3%-0.5% monopotassium phosphate + 0.2% urea to improve leaf photosynthetic efficiency and promote plump, robust shoot growth, which helps shoots stop growing and form terminal buds and differentiate into mixed flower buds; in autumn and winter, deep plow and expand the planting holes to improve the soil and apply base fertilizer early and heavily to raise the tree's stored nutrient level; covering the tree basin with grass, etc., creates a good environment of water, fertilizer, air and heat in the surface soil, and is an effective measure to promote pomegranate flowering, fruit set, vegetative growth and flower bud differentiation; adapting to the pomegranate's light-loving nature, adopt open canopy shapes such as the single-trunk natural open-center form and the three-main-branch open-center form to enhance light exposure, expand the range of effective branches and buds, and raise the nutritional level of branches and buds. Through opening up the canopy and pruning measures such as thinning branches and leaving long shoots, cultivate large numbers of short leaf-cluster branches that stop growing early in spring and summer. And through winter pruning and summer pruning, adjust the ratio of fruiting branches to vegetative branches to 1:5-10 to ensure the tree's nutrition supply to the fruit.

2 Extra-root fertilization during the flowering period

At full bloom, spray 0.2% urea + 0.3%-0.5% borax or 500 mg/l gibberellin, or from early flowering to full bloom spray 0.2% urea + 400-fold rare earth, to increase the fruit-setting rate.

3 Girdling at the flower bud stage

In early May at the flower bud stage, girdle 2-3 rings at the base of vigorous trees with few flowers or large branch groups, with the distance between rings more than 4 cm, to significantly increase the fruit-setting rate and promote flower bud differentiation in the current year.

4 Bee release in the orchard and artificial pollination

Pomegranate is an insect-pollinated flower; releasing bees in the orchard at full bloom can significantly increase the fruit-setting rate and fruit yield. Generally, placing one hive in the middle of an orchard of about 200 trees is sufficient, and bees need to be released when the temperature is above 11 degrees C. During the bee release period, absolutely do not spray highly toxic pesticides.

For orchards without a bee source during the flowering period, artificial pollination measures should be adopted. 1) Artificial flower-to-flower pollination. Pick off the open bell-shaped flowers that are shedding pollen and touch them against the open tubular flowers and gourd-shaped flowers, so that the pollen falls onto the stigma of normal flowers. This can be done at the same time as flower thinning. 2) Artificial pollen collection and pollination. During the flowering period, collect the flowers that have been thinned off, remove the petals, hold one flower in each hand and rub them together, so that the pollen falls onto newspaper. After drying in the shade, gather the pollen together and use a double-layer gauze bag to shake and pollinate or use a hand-held pollen duster to dust the normal flowers. This method is fast and suitable for pollination in large orchards.

5 Thinning buds, flowers and fruit

Timely thinning of degenerate flowers and excessive young fruit can effectively reduce the useless consumption of tree nutrients, increase the fruit-setting rate, and promote fruit development and flower bud differentiation. The method is: from bud emergence to full bloom, remove all bell-shaped flower buds and open bell-shaped flowers, and retain tubular flowers and gourd-shaped flowers. If there are enough gourd-shaped flowers, the tubular flowers (intermediate-type flowers) can also be thinned off together. Finally, around the fruiting branches bearing normal flowers, having 3-5 vegetative branches (with more than 100 leaves) is appropriate.