How to grow Robinia hispida from seed? Detailed propagation techniques

Robinia hispida, also known as the rose acacia, is a deciduous small tree or tree in the genus Robinia of the Fabaceae family. Its branchlets, peduncles and petioles are densely covered with fine brown bristles. It is renowned for its graceful tree form and rich, brilliant flower color. Its flowers are rose-red or pale purple, and its pods are 5-8 cm long and covered with glandular bristles. Its flowering period is from May to July. It is a rising star among garden trees and is usually propagated by grafting onto black locust rootstock.

Native to the Americas, it is cultivated in Beijing, Hebei, Shandong, Henan and Liaoning in China. It is propagated by grafting and is an excellent ornamental tree for courtyard and roadside greening.

Propagation techniques: It is usually propagated by grafting onto large black locust rootstock. Generally, black locust seedlings are used; select superior, robust seedlings and transplant them for cultivation for 4-5 years. Through root training and trunk training, two transplants with increased spacing between plants and rows, timely irrigation, fertilization, hoeing and loosening of soil, weed control, removal of buds and pruning, and strengthened tending and management during the seedling stage, trees are produced with straight trunks, smooth and thick growth, a tree height of more than 3.5 m, a diameter at breast height of more than 5 cm, and a diameter of more than 3 cm at the graft union. These are then selected as grafting rootstock.

To select and collect scions for grafting, first cut off the tip of the collected scions and the parts where the basal buds are not plump, and cut the scion branches into scions 10-12 cm long with 2-3 buds. Then, on both sides of the lower end, 3 cm below the lower bud of the scion, cut wedge-shaped slopes 2-3 cm long. When the rootstock is thicker than the scion, cut the lower end of the scion into a flat wedge shape, making the side with the terminal bud thicker and the other side slightly thinner, which helps the rootstock hold it and makes the graft union fit tightly. The cut surface of the scion should be flat and smooth, so that the cut surface easily fits closely against the split in the rootstock and the cambium on both sides heals easily. After the scion is cut, hold it in the mouth, taking care to keep it moist, to prevent water loss and contamination with soil.

For black locust rootstock, the rootstock can be cut or sawed off at a height of 3 m from the ground, and the cut should be trimmed into a smooth plane to facilitate healing. Use a cleft grafting knife to gently split two vertical cuts downward from the center of the cut surface of the rootstock, with the splits about 3 cm long.

After the rootstock is split, gently pry open the split with a cleft grafting knife and quickly insert the prepared scions respectively, so that the cambium of each scion and the rootstock align. When the rootstock is thicker, insert four scions at equal distances from each other; after they survive, they form a well-balanced, full, round crown, avoiding a lopsided crown and increasing the grafting survival rate.

When grafting, when inserting the scion, the cut surface should be exposed by 0.1-0.2 cm, so that the contact surface between the cambium of the scion and the rootstock is larger, which is beneficial to the formation and healing of meristematic tissue.

After joining, immediately bind tightly with plastic film strips to prevent the cambium of the scion and rootstock from shifting. Then put a plastic bag over it and tie it well, which helps keep the graft union moist and warm, benefits healing of the graft union, prevents air penetration and water loss, and effectively increases the grafting survival rate.

About 5-6 weeks after grafting, the healing and survival can be checked. Generally, after checking that the graft has healed and survived, promptly remove the binding plastic strips so as not to affect the growth and development of the rootstock-scion union.

After cleft grafting, after the scion sprouts, keep the robust shoots to form a well-balanced, full crown shape. All shoots emerging from the rootstock should be removed to ensure the growth and development of the grafted branch and to control ineffective consumption of nutrients and water. This promotes rapid growth and development of the top-grafted scion.

Finally, to make the grafted seedlings grow robustly and develop well, according to the soil fertility of the nursery and the growth needs of the grafted seedlings, irrigate and apply topdressing promptly and in appropriate amounts, regularly hoe, loosen soil and control weeds, so as to keep the soil loose and free of weeds and prevent the occurrence of seedling-stage pests and diseases. Strengthen the tending and management of grafted seedlings to cultivate high-quality, robust seedlings that meet the required specifications.