Key Technical Points for Soilless Propagation and Cultivation of Hawthorn

Hawthorn Propagation Methods

The seedlings used for potted hawthorn differ considerably from those used for field planting. For potted seedlings, the primary requirement is that within a relatively small range from the root crown, there should be well-developed fibrous roots; the greater the quantity of fibrous roots, the more favorable it is for growth after potting. In addition, according to the size of the pot used, seedling height is generally controlled at around 30 cm, with the trunk below 20 cm, and grafted seedlings are mostly used. Rootstock can be root-sucker seedlings or wild hawthorn seedling rootstock. When the seedling grows to about 30 cm in height, grafting is carried out after pinching (about 5 days later). Scions should be selected from cultivated varieties that flower and fruit early and have a high fruit-setting rate. Cleft grafting or bud grafting is commonly used. For cleft grafting, methods such as cleft grafting, cut grafting, side grafting, bark grafting and root grafting can be used, all with relatively high survival rates. Cleft grafting is mostly carried out around early spring before and after bud break. Bud grafting is mostly carried out from June to July, using T-shaped budding. After the grafted seedling survives, during the growing season, a sharp knife or spade can be inserted into the soil at 20 cm from the trunk to root-prune, including cutting off the main root of the seedling rootstock (generally at a depth of 20-30 cm). Root pruning can also be carried out through transplanting to shorten and trim the root system, thereby limiting the root range and increasing the amount of fibrous roots.

For the above-ground part, methods such as bending the trunk and pinching the new shoots in the early growth stage are used to control seedling height and lower the branching point of the trunk. According to the requirements of potted shaping, the nursery cultivation period can be extended, but generally potted planting can be done 1-3 years after the graft survives.

In-pot grafting can also be used, that is, after selecting rootstock for potting, grafting is used to achieve rapid shaping and rapid fruiting. In particular, in-pot grafting of perennial branch groups with flower buds has the obvious characteristics of a high survival rate and good fruit setting, and is an effective way to rapidly cultivate varieties with relatively high ornamental value.

Cultivation Management

For soilless potting of hawthorn, antique-style ceramic flower pots or plain pots (inner diameter 30 cm, height 25 cm) are mostly used. The cultivation substrate can be an equal mix of peat, barnyard manure soil and furnace slag, or an equal mix of vermiculite, barnyard manure soil and coarse sand. Potting is generally carried out in spring, when the seedlings have more stored nutrients in their bodies and can quickly take root and grow. When potting, first add a layer of ceramsite at the bottom of the pot as a drainage layer, then fill in the substrate and plant the seedling properly, and then add another layer of ceramsite on the surface of the pot to prevent watering from washing away the substrate. After potting, water thoroughly and place in a cool place for about one week. After new buds begin to sprout, gradually move to a place with sufficient light for normal management.

The nutrient solution for soilless cultivation of hawthorn can refer to the pomegranate nutrient solution formula, except that during the fruiting period the proportion of phosphorus and potassium in the nutrient solution can be appropriately increased. Normally, apply nutrient solution once every 10 days, with the amount each time depending on plant size. Water daily to keep the substrate alternately moist and dry; the tray at the bottom of the pot must not retain water for long periods, so as not to affect normal root growth. Before flowering and during the young fruit development stage, spray once each time with 0.2% potassium dihydrogen phosphate solution; during full bloom, spray 30-50 mg/L gibberellin 2-3 times (at 5-day intervals), which can increase the fruit-setting rate and promote young fruit development. For young trees bearing too much fruit, appropriate flower and fruit thinning is sometimes needed so that the remaining fruit grows better. The tree shape of potted hawthorn can be freely shaped according to the growth of the potted tree and the cultivator's preference. Various tree forms such as curved trunk, straight trunk, slanting trunk, layered and open-center are all acceptable. However, because hawthorn has obvious apical dominance, it is easy for the growth vigor of lower branches and buds to weaken. Therefore, when shaping, the tree (trunk) should be short rather than tall, the angle of main branches should be large rather than small, and upright branches on the back should be short rather than long, so that the branches extend outward, forming a slightly flattened crown, and promoting the development of thick, strong and short branches, which is conducive to flower formation and fruiting.

To promote flower bud formation in young vigorous potted hawthorn trees, fertilizer and water management from bud break to the early flowering stage is key. In addition, technical measures such as ring-barking and ring-cutting of the tree body, controlling the use of inorganic nitrogen fertilizer after mid-July, appropriately reducing water supply, and inhibiting the occurrence and vigorous growth of autumn shoots all have obvious effects.

After the fruit turns red in autumn until the end of the year is the ornamental period, and at the same time the winter dormancy requirement of the hawthorn tree must be met, so as not to affect next year's growth and fruiting. In North China, the method of burying in soil for cold protection can be used for overwintering; in Northeast China, cellars are mostly used for overwintering; in areas south of North China, covering the pot surface with grass or covering with grass in trenches can be used for overwintering.