Suitable Growing Environment and Management Techniques for Hawthorn

Hawthorn (Crataegus pinnatifida Bunge), also known as mountain hawthorn fruit or mountain red, belongs to the genus Crataegus in the rose family (Rosaceae) and is a deciduous tree reaching up to 6 m in height. It is distributed in Shandong, Shaanxi, Shanxi, Henan, Jiangsu, Zhejiang, Liaoning, Jilin, Heilongjiang, Inner Mongolia, Hebei and other places.

Ecological conditions required for hawthorn cultivation:

1. Temperature. Hawthorn has a relatively wide tolerance for temperature; it can be grown in areas with an annual average temperature of 4.7-16°C, with 12-15°C being the most suitable zone for development. The highest temperature hawthorn can endure is 43.3°C, and it can tolerate 40°C high temperatures for relatively long periods. Climate conditions vary from place to place, and each location has its own most suitable cultivation type or variety. Different varieties in different places have different accumulated temperature requirements, with a minimum of 2000°C and a maximum of 7000°C; the annual growth period is 180-220 days, the daily average temperature required for sprouting and shoot growth is 13°C, fruit development requires 20-28°C, and the optimum temperature is 25-27°C.

2. Water. Hawthorn is relatively drought-tolerant and highly adaptable. Hawthorn is more drought-tolerant than apples and pears; in some arid areas where apples and pears cannot be planted, hawthorn still grows well, and it is even more drought-tolerant than peaches. However, drought can seriously affect fruit growth and development, making fruits smaller, causing severe fruit drop and reducing yield. If drought occurs in the early growth stage, large numbers of flowers and fruits drop, and in particularly dry conditions it can even cause tree death. When soil moisture content is 9.34%, this is the safe moisture content for hawthorn; at 7.9% moisture content, wilting is observed; the lethal humidity is 5.8%. Generally, it grows well in areas with annual rainfall of 500-700 mm. Hawthorn is also relatively waterlogging-tolerant; in rainy years or seasons, even if water accumulates for about a week, it can still grow normally, but it is not resistant to sudden rainstorms, because hawthorn's root system is relatively shallow, often resulting in canopy leaning or tree toppling.

3. Light. The hawthorn canopy has very strict light requirements, and light has a great influence on fruiting. In naturally growing or extensively managed hawthorn orchards, fruiting is obviously concentrated on the outer canopy, and alternate bearing is prone to occur. The most fruit is produced when daily available light reaches more than 7 h; 7-5 h gives good fruiting; 5-3 h basically cannot set fruit; and less than 3 h of direct light per day means no fruit set or very little fruit set.

Planting

Hawthorn's new roots emerge relatively early in spring, so autumn planting is preferable. The spacing between plants and rows is 3~4 m on poor, thin soil, and 4~5 m on fertile, flat ground. When planting, it is advisable to mix and plant 2~3 varieties in separate rows to increase the fruit-setting rate. At planting, apply 100 kg of farmyard manure, 15 kg of urea, 20 kg of superphosphate and 10 kg of potassium sulfate per tree.

Training and pruning

According to the growth characteristics of hawthorn branches, use the open-center stratified form, the multi-main-branch natural round-headed form, or the natural open-center form for training. Because the hawthorn trunk is relatively weak in apical dominance, it easily develops a leaning trunk or unbalanced crown; during training, the direction of the pruning cut bud can be used, or the extension branch of the central leader can be replaced to control and adjust this. When the central leader is seriously leaning and difficult to train, the central leader can also be removed in accordance with its growth tendency, changing the tree to the natural open-center form. Keep 3~4 main branches on the whole tree, with a base angle of 45°~50°, and then appropriately train secondary main branches on each main branch to occupy space. When using the multi-main-branch natural round-headed form for training, according to the natural growth tendency of the branches, keep main branches spaced about 30 cm apart and appropriately scattered and arranged, extending outward in all directions, cultivating a total of 6~7 main branches on the whole tree.

For hawthorn trees in full fruiting stage, the main task is to alternately renew and rejuvenate the fruiting mother branches that have borne fruit for several consecutive years by heading back, to prevent the fruiting area from moving outward, stabilize yield, and maintain good growth vigor. In particular, for branch groups that bear many fruits and droop, heavier heading back should be done on 3~5-year-old branch sections. When alternate bearing occurs due to excessive fruiting, excessive fruiting mother branches should be thinned out on on-year trees so that the ratio of mother branches to vegetative branches remains 2:1 or 1:1. Pre-bloom supplementary pruning can also be done at the bud stage, thinning out some inflorescences on weak branches to promote flower bud differentiation. When the canopy is seriously crowded, first thin out or head back some large branches, and at the same time thin out some vegetative branches.

Soil, fertilizer and water management and other matters

Soil management. Deep plowing and soil maturation is a basic measure in yield-increasing techniques; deep plowing and maturation can improve the soil, increase soil permeability, and promote tree growth.

Fertilizer and water management. Apply base fertilizer early in autumn; topdressing can be applied during several periods such as bud break and leaf expansion, flowering and fruiting, and fruit enlargement, according to specific conditions. After fruit harvest in late autumn, apply sufficient base fertilizer in time to supplement tree nutrition; base fertilizer should be mainly organic fertilizer, applying 4000~5000 kg of organic fertilizer per 667 sq m in trenches, and the amount of chemical fertilizer applied depends on the tree's condition. Topdressing at the spring flowering stage and foliar spraying of boron (using 0.5% boric acid solution) can significantly increase the fruit-setting rate and promote new shoot growth. For on-year trees, topdressing in the later stage (August~September) should be strengthened to promote flower bud differentiation. When drought causes fruit drop, irrigation or loosening the soil and covering with grass should be carried out to reduce the drought.

Other aspects. In production, hawthorn sometimes experiences severe flower and fruit drop, affecting yield. Causes include weak tree vigor, poor pollination and fertilization, soil drought, insufficient light, etc., and corresponding measures should be taken for different situations. For fruit drop or flowers that fail to set fruit due to poor pollination and fertilization, a 50 mg concentration gibberellin solution can be sprayed from the early flowering stage to the full flowering stage, focusing on spraying the flower clusters, which can increase the fruit-setting rate by more than 1~2 times and also make the fruit color and mature earlier.