How to make and care for a rhododendron bonsai?

Rhododendron, also known as yingshanhong, is an evergreen or deciduous shrub of the genus Rhododendron in the family Ericaceae. The plant is much branched, with slender, straight branches bearing brown or brownish rough hairs. The leaves are simple and alternate, ovate-elliptic to needle-shaped, with acute or slightly blunt tips, and sparsely covered with brown stiff hairs on the surface. Several flowers cluster at the tips of the branches; the corolla is funnel-shaped, single or double, and comes in a rich range of colors including white, pink, red, purple and various bicolors. There are many varieties of rhododendron, broadly divided into four main groups: spring rhododendron, summer rhododendron, spring-summer rhododendron and Western rhododendron. Using it to make a bonsai gives the qualities of a gnarled and antique-looking root and trunk, small and dense leaves, jade-green leaf color, tolerance of pruning and a great variety of flower colors.

Rhododendron can be propagated by layering, cuttings, division and grafting. Old rhododendron stumps that have grown for many years and have quaint, unusual roots and trunks can also be used to make bonsai; they are usually dug up and transplanted in late autumn and early winter or in spring before the flowers fade. When transplanting, keep plenty of the original soil, prune the main trunk and main roots appropriately, cut off branches that would interfere with the shape, and retain as many lateral roots and fibrous roots as possible; large branches and trunks should be carefully examined and removed only after confirming they are not needed for the design. First plant them in a clay pot or in the ground to grow out the raw material. The soil should be a well-drained sandy soil. For stumps dug in late autumn and early winter, after planting, bury them completely with sandy soil, leaving only a little of the branches exposed, water thoroughly, then cover with a plastic bag to keep them warm and humid; stumps dug in spring should also be buried 2/3 into the soil. After planting, keep the soil moist but not waterlogged. Once the plant has established and sprouted, gradually remove the sandy soil from around the trunk. During the raw-material growing period, spray water on the leaves and trunk frequently to increase air humidity, but do not let the roots become too wet; especially avoid waterlogging, otherwise the roots will rot. In summer, provide shading to prevent scorching by the hot sun.

Rhododendron can be made into many bonsai styles, including formal upright, slanting, curved-trunk, twin-trunk, multi-trunk, exposed-root, cascade, rock-clinging and water-and-land styles. For seedlings propagated by cuttings, layering and similar methods, shaping can be carried out year by year after 3 to 4 years of growth. Shaping is usually done before bud break in spring or during the summer and autumn growing seasons. The method is mainly pruning, with wiring as a supplement. When shaping, follow the principle of working from thick to thin: wire the main trunk and main branches appropriately, and shape the other branches by pruning. Because rhododendron branches and trunks are relatively brittle and break easily, handle them carefully. During the growing season, if a branch cracks, smear yellow mud on the wound, wrap it with plastic film, and it will heal and recover quickly. Old rhododendron stumps, however, must be shaped mainly by pruning, though some branches can also be wired appropriately. To improve ornamental value, you can also use an old stump of Rhododendron mucronatum that has grown for many years, with thicker branches and an elegant form, as the rootstock, and use a superior variety of rhododendron as the scion, grafting by approach grafting or cut grafting. Depending on the condition of the stump, part of the soil can also be gradually removed and the roots raised above the soil surface, exposing the roots and claws to give a quaint and vigorous look.

Rhododendron likes a warm, humid, semi-shaded environment and requires good ventilation. At ordinary times it can be placed in bright light for care. In the high-temperature seasons of summer and early autumn, provide shading to avoid scorching by the hot sun, otherwise strong light will burn the leaves; but it should not be too shaded either, lest the plant grow leggy and flowering be affected. It can be kept under a shade shed or in the shade of trees. During the growing season, keep the soil moist but not waterlogged; pay attention to drainage in the rainy season. When the air is dry, sprinkle water on the plant and the surrounding ground to increase air humidity and prevent the leaves from drying up. You can also cover the surface of the potting soil with a layer of soft grass to prevent the hot sun from burning the fine fibrous roots on the soil surface. Apply a thin, well-rotted liquid fertilizer about once every 15 days. To prevent chlorosis, add a small amount of black alum to the fertilizer solution so the leaves become dark green and glossy. At the bud stage, apply 1 to 2 additional doses of phosphorus fertilizer such as bone meal or superphosphate to encourage larger and more vividly colored flowers. In winter, move it indoors to a sunny place, keep the soil above 0°C so it does not freeze, and control watering so the potting soil is only slightly moist. Prune once every year after flowering, cutting off diseased and insect-damaged branches, dead branches, crossing branches, overlapping branches, weak twigs and leggy shoots; also shorten overly long branches appropriately, so the plant shape is elegant and the branches are reasonably distributed, strengthening the inner canopy and the growth of the plant. Repot once about every 2 years in spring or late autumn. The potting soil should be a fertile, loose, slightly acidic sandy soil rich in humus.