Cultivation Techniques and Daily Care Methods for Oleander
Oleander (Nerium oleander), also known as willow-leaf peach or half-year red. Belongs to the family Apocynaceae, genus Nerium. It gets its name because its flowers resemble peaches and its leaves resemble bamboo. The flower colors are gorgeous - either pink, like peach blossoms, full and vivid; or pure white, bright and clean as snow, sparkling and striking. It has been appreciated by people since ancient times. Cultivated everywhere, it is an excellent flowering shrub that blooms in summer and autumn and can resist pollution.
(I) Morphological Characteristics and Varieties
Evergreen large shrub, plant height can reach 4 m to 5 m, crown spreading, branches upright and smooth, clumping, young branches angular, strong branching ability, mostly growing in a three-forked pattern. Leaves lanceolate, usually 3 to 4 in whorls, mostly opposite on the middle and lower parts of branches, thick leathery, midrib prominent, entire margin, with short petioles, containing a small amount of milky sap in branches and leaves. Cymes terminal, corolla funnel-shaped, 5-lobed, petals wrinkled, lobes twisted to the right, pink to deep red, most are double-flowered and semi-double-flowered. Flowering period long, from June to October, with successive blooms. Fruit oblong, many horticultural varieties, common ones include white-flowered oleander, red-flowered oleander, etc.
(II) Ecological Habits
Oleander is native to India, Iran, and Afghanistan. It prefers warm and humid climates and has weak cold resistance. It can be planted outdoors in areas south of the Yangtze River basin in China, but in Nanjing the branches and leaves sometimes freeze and wither, and small seedlings may even freeze to death. In the north it can only be grown in pots for ornamental purposes, overwintering indoors. The white-flowered variety has slightly stronger cold resistance than the red-flowered variety. Oleander is not tolerant of waterlogging and requires planting in high, dry, and well-drained locations. It likes light and fertilizer, and can also adapt to relatively shady environments, but when planted in shade, it produces fewer and paler flowers. It has strong resistance to air pollution, with strong resistance to toxic gases such as sulfur dioxide, chlorine gas, and smoke and dust, and also has strong absorption capacity, making it an excellent tree species for greening and decorating industrial and mining areas and railway platforms. It has strong sprouting ability, and the tree body recovers easily after damage.
(III) Propagation Methods
Mainly by cuttings, but also by division and layering. Cuttings can be done in both spring and summer. Soak the base of the cuttings in clean water for about 10 days, keeping the soaking water fresh; after planting, they will root earlier and the survival rate will also be high. The specific method is: in spring, cut 1 to 2-year-old branches into 15 cm to 20 cm stem segments, bundle about 20 into a bunch, soak in clean water with the submerged depth being 1/3 of the stem segment, change the water at the same temperature once every 1 to 2 days, keeping the temperature at 20°C to 25°C, and when adventitious roots are found at the submerged part, they can be planted. When planting, make holes in the cutting medium with bamboo chopsticks to avoid damaging the adventitious roots. Since the sprouting ability at the base of old oleander stems is very strong, a large number of young shoots are often produced, and these branches can be fully utilized for summer softwood cuttings. Select semi-lignified cuttings, keep the top 3 small leaves, insert into the substrate, pay attention to timely shading and water management, and the survival rate is also very high. For layering propagation, first notch or girdle the part to be buried, bury it in soil, and after about 2 months it can be cut from the mother plant, and transplanted with soil the following year.
(IV) Cultivation Techniques
Oleander has strong adaptability, and cultivation and management are relatively easy; whether planted in the ground or in pots, it is relatively low-maintenance. For ground planting, transplanting should be done in spring, and heavy pruning should be carried out at transplanting. Pay attention to protection in winter. Branches and leaves are susceptible to scale insect damage, so attention should be paid to prevention and control.
Potted oleander, in addition to requiring good drainage, also needs sufficient fertility. In spring, shaping and pruning are needed when it sprouts. For leggy branches and weak slender branches on the plant, they can be cut off from the base, and for overly dense inner branches, part should also be thinned out, so that the branches are evenly distributed and the tree shape remains full. After 1 to 2 years, repot once, and repotting should be done after pruning. Summer is the period of vigorous growth and flowering for oleander, and the water demand is large. In addition to watering once each morning and evening every day, if the pot soil is too dry, an additional spraying should be added to prevent young branches from wilting and affecting flower longevity. After September, water should be withheld to inhibit continued growth of the plant, make branch tissues mature, increase nutrient accumulation, and facilitate safe overwintering. The overwintering temperature needs to be maintained at 8°C to 10°C; below 0°C, it will shed leaves.
Oleander is a fertilizer-loving plant. For potted plants, in addition to applying sufficient base fertilizer, fertilizer should be top-dressed once a month during the growing period.
(V) Ornamental Value and Applications
In the season when few flowers bloom in summer, oleander blooms for nearly 4 months, making it a rare summer flowering tree species. It can be planted on either side of buildings, in parks, green spaces, roadsides, poolside, and other locations, and is even more suitable for planting in industrial and mining areas and along railway lines for pollution resistance.
The stems and leaves are toxic; attention should be paid during pruning and cutting.