How to Grow Osmanthus? Detailed Guide to Cultivation Methods and Precautions
Osmanthus is the common name for many trees in the genus Osmanthus in China, also known as rock osmanthus, wood osmanthus, golden millet, and so on. It is an excellent garden tree species that combines greening, beautification, and fragrance, with both ornamental and practical value. Its fragrance is pure enough to clear the air and strong enough to carry far, making it truly unique. It has been deeply loved by Chinese people since ancient times and is regarded as a traditional famous flower. Let us take a look at the cultivation methods and precautions for osmanthus below!
Growth Habits of Osmanthus
1. Osmanthus prefers warmth and has strong stress resistance. It tolerates both high temperatures and relatively cold conditions. In areas south of the Qinling Mountains and the Huaihe River in China, it can overwinter outdoors.
2. Osmanthus prefers sunlight but also tolerates shade. Under full sunlight, its branches and leaves grow lush and it blooms profusely. In shaded areas, its branches and leaves grow sparse and it blooms sparsely.
3. Osmanthus likes moisture and fears waterlogging. However, it also has a certain degree of drought tolerance. If subjected to waterlogging damage, the entire plant may die.
4. Osmanthus has low requirements for soil. It can generally grow in any soil except alkaline soil, low-lying areas, or soil that is too heavy and poorly drained.
Propagation Methods of Osmanthus
1. Sowing: Osmanthus fruit usually ripens from April to May. After harvesting, sprinkle water and pile it up for composting, remove the flesh, place it 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 soil well and apply sufficient base fertilizer. They can also be sown in indoor seedbeds. When sowing, place the seed with the hilum facing sideways to avoid bending of the radicle and young stem, which would affect seedling growth in the future.
2. Grafting: For osmanthus, before spring sprouting, cut the rootstock at 5 cm above the ground. Cut a vigorous 1- to 2-year-old osmanthus branch 10 to 12 cm long, shave one side of the base into a 2 to 3 cm cut surface, and cut the opposite side into a small 45-degree slope. Make a vertical cut about 2 to 3 cm deep at about one-third of one side of the rootstock, insert the scion into the cut, align the cambium layers, tie tightly with a plastic bag, and then bury in soil for cultivation.
3. Cuttings: Osmanthus cuttings are usually taken before spring sprouting using fully developed one-year-old branches, cut into 5 to 10 cm lengths, with the lower leaves removed and 2 to 3 green leaves kept at the top. Insert them into river sand or loess seedbeds at a plant-to-row spacing of 3*20 cm. After inserting, water or spray promptly, shade them, and maintain a temperature of 20 to 25 degrees C and a relative humidity of 85 to 90 percent. After 2 months, they can root and be transplanted.
4. Layering: For the low-branch layering method of osmanthus, from spring to early summer, select relatively thick 1- to 2-year-old branches on the lower part of a low-trunk mother tree, choose a section that bends easily, cut or girdle it with a sharp knife, press it into a 3 to 5 cm deep trench, and fix the pressed branch with a wooden stick. For the air-layering method, in spring select a vigorous 1- to 2-year-old branch from the mother tree, make a ring cut or girdle as in the low-branch layering method, then apply culture medium to the wound, tie plastic bags tightly above and below, and after roots develop in autumn, cut it from the mother plant for care.
Cultivation Methods of Osmanthus
1. Potting soil: Osmanthus does not have high requirements for soil. The potting soil can be a mix of humus soil or peat, garden soil, and sandy soil or river sand (ratio 5:3:2). After preparation, the pH should be maintained at 5.5 to 6.5. Before potting, disinfect the growing soil with a 0.1 percent potassium permanganate solution.
2. Watering: For osmanthus watering, grasp the principle of not watering until dry, and when watering, water thoroughly. Spray clean water on the leaf surface once a day. After Qingming Festival, move the osmanthus to the open air and water it thoroughly once. In summer, water in the morning and evening; in winter, water around noon. Be careful not to let water accumulate.
3. Fertilizing: Osmanthus is mainly grown for its flowers, so it should be supplied with sufficient fertilizer. During shoot growth, apply nitrogen fertilizer 1 to 2 times. Before flower bud differentiation and flowering, mainly apply phosphorus fertilizer. Before fertilizing, the potting soil should be slightly dry, and it is advisable to loosen the soil first. On the second day after fertilizing, water once.
3. Repotting: Osmanthus usually needs repotting and soil replacement once every 2 to 3 years. Cut off part of the old roots and dead roots, place a layer of river sand or vermiculite at the bottom of the pot to improve aeration and drainage, and place decomposed cake fertilizer as base fertilizer. Be sure to press the added soil firmly.
4. Pruning: Shaping of osmanthus is best done after autumn. For plants with very poor tree shape, cut off all the top branches at 2/3 or 3/4 of the height. For plants with overly dense branches, thin them out. After flowering, also cut off leggy branches, dead branches, pest- and disease-damaged branches, and dense weak branches.
5. Overwintering: The suitable room temperature for osmanthus overwintering is 0 to 5 degrees C, with a relative humidity of 50 to 80 percent. In winter, the cold room should have good light, especially before the buds begin to sprout in early spring, when sufficient sunlight is even more required. The following year, after Grain Rain, arrange to move them outdoors. After moving out, first place them together in a wind-sheltered, sunny spot outdoors.
6. Diseases: Common diseases of osmanthus include leaf spot, sooty mold, algal leaf spot, root rot, and iron deficiency. For leaf spot, sooty mold, and algal leaf spot, Bordeaux mixture or carbendazim can be sprayed for control. For root rot, attention should be paid to keeping the soil loose and breathable, and avoiding water accumulation.
7. Pests: Common pests of osmanthus include sawflies, whiteflies, mites, white peach scale, and yellow slug moths. Sawflies, whiteflies, and mites can be sprayed with dimethoate for control. For white peach scale, besides manual brushing off, omethoate or fenitrothion can be sprayed during the first and second instar nymph stages.
Precautions for Osmanthus
1. Water management for potted osmanthus is relatively difficult. Overwatering often causes leggy growth, while poor drainage and water accumulation in the pot can easily cause root rot. Therefore, in daily care, be sure not to water too much. Even in the early flowering stage when water demand is relatively high, avoid making the potting soil too wet.
2. Osmanthus is a long-day plant and likes strong light. If the plant does not receive sufficient light during the growth period, its branches and leaves will become leggy, affecting flower bud formation and causing failure to bloom. Therefore, do not shade it excessively during cultivation.
3. If potted osmanthus is not repotted and the soil is not changed for years, the plant will suffer from insufficient nutrition, and the root system will become tangled and unable to spread, affecting flowering. For this reason, potted osmanthus should be repotted once every 1 to 2 years, and a small amount of hoof pieces should be applied as base fertilizer. Throughout the growing period, more phosphorus and potassium fertilizers should be applied.
4. After potted osmanthus is moved indoors in winter, it should be placed in a low-temperature area to allow it to go dormant. If the room temperature is relatively high, the osmanthus will not achieve full dormancy, which will cause it to sprout and unfold leaves early, leading to weak branches and consumption of large amounts of nutrients. After being moved outdoors in spring, it is prone to shriveling and dying when encountering dry wind.
5. Potted osmanthus is not tolerant of smoke and dust. If allowed to grow in places with polluted air, it will grow poorly, with smaller leaves that easily fall off, and few or no flowers. Therefore, during cultivation, prevent osmanthus from being polluted by smoke and dust.