What are the cultivation techniques for osmanthus trees? A detailed guide
Osmanthus is an evergreen shrub or small tree of the genus Osmanthus in the family Oleaceae, also known as rock osmanthus, jiulixiang, and jinsu. It is an excellent garden tree that combines greening, beautification and fragrance, with both ornamental and practical value. In ancient Chinese poetry praising flowers, the number of works praising osmanthus is also considerable, and it has been deeply loved by Chinese people since ancient times. Let's take a look at the cultivation techniques for osmanthus trees below!
Variety classification of osmanthus trees
1. Four-season osmanthus variety: The four-season osmanthus is a clumping shrub with a low tree form, short and dense branches, and a round spherical crown. New leaves are dark red, while mature leaves are green or yellow-green. The leaves are elliptical to broadly ovate, with a large angle between the main vein and lateral veins, approaching a perpendicular state. Flower buds are usually solitary or 2-3 stacked together, blooming in batches from September each year to March of the following year, with a fragrance less rich than that of silver osmanthus, golden osmanthus, and red osmanthus. Common varieties include large-leaf four-season osmanthus and small-leaf four-season osmanthus; varieties that bloom in all four seasons include yueyuegui, rixianggui, large-leaf fodingzhu, and serrated-leaf four-season osmanthus.
2. Red osmanthus variety group: Red osmanthus is dioecious, with a round spherical crown, light gray bark that is relatively smooth, and sparse lenticels. The leaves are leathery, oblong or elliptical, with a relatively flat leaf surface, revolute leaf margins, entire margins, occasionally with sparse teeth at the apex, a broad cuneate base, and an obtuse or shortly pointed apex, with 8-10 pairs of lateral veins, reticulate veins obvious on both sides, and a petiole 8-10 mm long. The flowers are orange-red, the corolla is slightly incurved, the fragrance is light, and the flowering period is from late September to early October. There are varieties such as large-flowered red osmanthus, toothed red osmanthus, cinnabar red osmanthus, and broad-leaf red.
3. Golden osmanthus variety group: The golden osmanthus has a round spherical crown, a vigorous tree habit, upright branches, and is very dense. The bark is gray, the lenticels are round or elliptical, and the spring shoots are relatively stout. The leaf color is dark green, the leaves are elliptical, the leaf surface is uneven, and the leaf margins are slightly wavy. The flowers are yellow, strongly fragrant, and do not set fruit. It blooms in autumn, with flowers ranging from lemon yellow to pale golden yellow. Varieties include large-flowered golden osmanthus, large-leaf yellow, Huangchuan golden osmanthus, late golden osmanthus, round-leaf golden osmanthus, Xianning late osmanthus, ball osmanthus, round-petal golden osmanthus, willow-leaf Su osmanthus, Jinshi osmanthus, and wave-leaf golden osmanthus.
4. Silver osmanthus variety group: The silver osmanthus has a round spherical crown, spreading large branches, dense branches and leaves, and good growth. The bark is light gray, and the lenticels are numerous and large, shaped like snowflakes, very conspicuous. The leaves are green or dark green, oblong or elliptical, relatively broad and thick, with a relatively flat leaf surface. It blooms in early to mid-September, with flowers from creamy yellow to lemon yellow, a rich fragrance, and does not set fruit after flowering; it blooms in autumn. Varieties include broad-leaf seed silver osmanthus, willow-leaf silver osmanthus, hard-leaf silver osmanthus, seed silver osmanthus, Jiulong osmanthus, early silver osmanthus, late silver osmanthus, Baijie, pure white silver osmanthus, and Qingshan silver osmanthus.
Growing environment for osmanthus trees
1. Temperature: Osmanthus trees prefer warmth. In growing areas, the average temperature is 14-28°C, the average July temperature is 24-28°C, and the average January temperature is above 0°C. It can withstand a minimum temperature of -13°C, and the most suitable growing temperature is 15-28°C. It can overwinter outdoors in areas south of the Qinling Mountains and the Huai River in China. It is not very cold-resistant, but compared with other evergreen broadleaf tree species, it is still a relatively cold-resistant tree species.
2. Water: Osmanthus trees prefer moisture. Humidity is extremely important for the growth and development of osmanthus, requiring an average annual humidity of 75-85% and annual precipitation of about 1000 mm. Especially during the young stage and when adult trees bloom, more water is needed; drought will affect flowering. Waterlogging must be avoided, but it also has a certain drought tolerance.
3. Light: Osmanthus prefers sunlight but can also tolerate shade. Under full sunlight, its branches and leaves grow luxuriantly and it blooms profusely; in shaded places, the branches and leaves are sparse and flowers are few. If potted indoors in the north, special attention should be paid to sufficient light to promote growth and flower bud formation. Strong sunlight and deep shade are unfavorable for its growth. Generally, 6-8 hours of light per day are required.
4. Soil: Osmanthus is not very demanding about soil. Except for alkaline soil, low-lying land, or soil that is too clayey and poorly drained, it can generally grow. However, deep, loose, fertile, well-drained slightly acidic sandy loam is most suitable.
5. Air: Osmanthus has a certain resistance to harmful gases such as chlorine, sulfur dioxide, and hydrogen fluoride, and also has a strong ability to absorb and retain dust. It is suitable for planting in ventilated and light-transmitting places. It likes a clean and well-ventilated environment and is not tolerant of smoke and dust damage; after being harmed, it often fails to bloom.
Propagation techniques for osmanthus trees
1. Sowing: Osmanthus fruit usually matures from April to May, and can be harvested when the peel changes from green to purple-black. Osmanthus seeds have after-ripening and require at least half a year of sand storage. After harvesting, sprinkle water and pile them for fermentation, remove the pulp, place them in a cool place to let the seeds dry naturally, and store them mixed with sand. After sand storage, they can be sown in autumn or spring. Before sowing, prepare the land well and apply sufficient base fertilizer; they can also be sown in indoor seedbeds. When sowing, place the seed hilum facing sideways to avoid bending the radicle and young stem, which would affect seedling growth in the future.
2. Grafting: Osmanthus grafting rootstocks mostly use privet, small-leaf privet, waxleaf privet, water wax, etc. When propagating seedlings in large quantities, small-leaf privet is mostly used. Before spring sprouting, cut off the rootstock 5 cm above the ground. Cut 1-2-year-old strong osmanthus branches 10-12 cm long, cut one side of the base into a 2-3 cm cut surface, and cut the opposite side into a small 45-degree bevel. Make a vertical cut about 2-3 cm deep at about 1/3 of one side of the rootstock, insert the scion into the cut, align the cambium, tie it tightly with a plastic bag, and then bury it in soil for cultivation.
3. Cuttings: Osmanthus cuttings usually use one-year-old fully developed branches before spring sprouting, cut into 5-10 cm lengths, remove the lower leaves, leave 2-3 green leaves at the top, and insert them into a river sand or loess seedbed at a plant-row spacing of 3*20 cm. After inserting, water or spray promptly, shade, maintain a temperature of 20-25°C and a relative humidity of 85-90%. After 2 months, they can take root and be transplanted.
4. Layering: Osmanthus can be propagated by low layering and air layering. The low layering method is to select 1-2-year-old branches on the lower part of a relatively stout low-trunk mother tree from spring to early summer, choose an easily bendable part, cut with a sharp knife or girdle it, press it into a 3-5 cm deep trench, and fix the pressed branch with a wooden stick. The air layering method is to select 1-2-year-old stout branches from the mother tree in spring, cut a ring or girdle them as in the low layering method, then apply culture medium to the wound, tie plastic bags tightly above and below, and after rooting in autumn, cut them off from the mother plant for maintenance.