Rhododendron, or Rosewood
The genus of rhododendrons is large and diverse. But the rose from the family of rosaceae rhododendron from the heather family has nothing to do. They are connected only by the beauty of flowering and a huge variety of species and varieties.
Description of Rhododendron
Rhododendron (Rhododendron) - a genus of plants of the Heather family. A vast genus that unites about eight hundred species of evergreen, semi-deciduous and deciduous shrubs and trees.
The rhododendron genus includes azaleas widely known in indoor and greenhouse floriculture, which are distinguished by some taxonomists as a subgenus or section of the genus.
Rhododendrons are distributed mainly in the temperate zone of the Northern Hemisphere, with the greatest diversity of species observed in South China, the Himalayas, Japan, Southeast Asia, and North America. They are also found in the southern hemisphere - in New Guinea and in the northeast of Australia. Plants vary greatly in size: some species reach a height of 30 m, but there are also creeping shrubs. The size of flowers - from tiny to having more than 20 cm in diameter.
In Russia, under natural conditions, up to 18 species are found, mainly in the Caucasus (for example, yellow rhododendron), in Siberia and the Far East.
Choosing a Place to Plant Rhododendron
A very important point - the right place to plant a rhododendron bush. Rhododendrons dictate their conditions, and they are whimsical in choosing lighting, soil and neighbors - it is not always easy to fit a new bush into an already formed plant community.
The place for planting rhododendrons should be protected from the prevailing winds and direct sunlight, without stagnation of water and with an acid reaction of the soil.
All rhododendrons need sun, but to varying degrees. Alpine dwarfs are especially sun-loving. Most large-flowered evergreens prefer to grow in partial shade. Some put up with periodic shading, but rhododendrons cannot stand a constant shadow - then they generally do not bloom or bloom very weakly. Pines are considered an ideal neighbor for them - under them there is enough light, and a deep root system does not interfere with a flowering shrub.
By the way, this is another prerequisite for planting rhododendrons - so that there are no large trees with a superficial root system near the landing pit. Such as maples, linden, alder, willow, and especially birch, their roots drastically dry out and deplete the soil, and it is difficult for rhododendrons to compete with them. To protect the rhododendron from the underground aggression of large neighbors, the landing hole can be isolated from below and from the sides with a solid piece of dense non-woven covering material.
Years of experience show that these plants feel good near ponds where the air is moist. Therefore, they are planted near ponds and lakes, streams and pools. If there is no water nearby, the evergreen rhododendrons are sprayed once a week before flowering. But flowering plants should not be doused with water; it is better to water the bushes more often.
Features landing rhododendron
The best time to plant rhododendrons is spring. During spring planting, plants are able to adapt well and take root in a new place. And you will have the opportunity to admire the first flowering. Plants with a closed root system (in the container) can be planted at a later date.
At the chosen place, landing pits are prepared in advance. The root system of rhododendrons is quite compact, therefore, even for tall species, it is enough to dig a hole about 50 cm deep and 70-80 cm wide. The distance between plants depends on the height and diameter of the crown of the bush and averages from 0.7 to 2 m. Drainage to the bottom pits are required: a layer of broken brick and sand is 15-20 cm, if the landing pit is deep, then the drainage layer increases to 30-40 cm and includes fine gravel or crushed stone (but not lime!).
It should be remembered that in nature rhododendrons grow on acidic, humus-rich, loose, air- and water-permeable soils. Therefore, the garden substrate should be appropriate: a mixture of leafy soil, high peat, litter of coniferous trees (3: 2: 1) with the addition of full mineral fertilizer: 70 g per pit. The optimum acidity of the soil is 4.5-5.0.
Before planting, the root ball of the rhododendron removed from the pot should be well saturated with water. If it has dried up, it is immersed in water and wait for the cessation of the release of air bubbles. The bush is planted in a pit filled with substrate, making sure that the root neck is not deepened, but is 2-4 cm higher than the soil level, taking into account its precipitation. Around the bush make a near-stem well with raised edges and watered abundantly.
Rhododendrons have a shallow, sensitive root system (30-40 cm), which develops mainly in the litter and the humus horizon. Therefore, around the planted bushes, mulching material is necessarily poured, preserving moisture, preventing overheating of the soil and weed growth, protecting the roots from mechanical damage, reducing the depth of freezing of the soil. As a mulch, pine bark or wood chips, coniferous litter, peat are best suited, while the layer of mulch should be at least 5 cm.
Properly planted rhododendrons take root well. If the soil substrate was made qualitatively, they will not require special care.
In the hot and dry summer and even autumn months, it is necessary to ensure that the soil under the bushes does not dry out. However, do not get carried away - excess watering is harmful to them.
Since in the mountains these plants live in conditions of high humidity, as a rule, they respond very well to spraying the entire bush with leaves and flowers. Naturally, this should not be done under the scorching sun or ice water.
It is best watered with rain or river water. Water from an artesian well or water supply contains many salts of calcium and magnesium - in this case, the soil will begin to alkalize and become saline, and rhododendrons will lose their decorative effect. (At first, nothing seems to be happening, but after 2–4 years, hard water will do the trick.)
So that the soil substrate does not alkalize, water for irrigation must be acidified - best of all with sulfuric acid. It is difficult to indicate the exact concentration of acid - it depends on the degree of hardness of the water. The easiest way to use litmus indicator paper. The hydrogen index (pH) of water should be 3.5–4.5.
Withered inflorescences that reduce the decorativeness of the plant must be broken off or carefully pruned, keeping axillary buds at the upper leaves. This contributes to the abundant growth and flowering of rhododendrons next year.
Wintering is the most important stage in the life of rhododendrons. The flowering of the next year depends on it.
As a rule, deciduous species winter in the middle zone better than evergreens. Such deciduous rhododendrons such as Daurian, Japanese, yellow, Canadian, Ledebour, Schlippenbach do not need to be covered - just in case, cover only the zone of the root neck with dry leaves or peat.
More complicated is the case with evergreen rhododendrons. Even winter-hardy (Caucasian, Katevbinsky) is best grown with shelter. In winter, they do not freeze as much as they dry out — they need protection from the wind and the sun. For this purpose, houses are good, knocked down from boards and covered with roofing material.
Less winter-hardy evergreen rhododendrons will not protect such a shelter. They will need houses covered with porous insulation material (polypropylene, polyurethane foam, etc.). Fragile heaters (polystyrene) are unsuitable. Shelter must have a frame, otherwise the fallen snow will bring it down and break the bush.
Frost can damage the root system of rhododendrons, both evergreen and deciduous, so it must be insulated first. As soon as low temperatures are established, the roots are mulched with acid peat or a dry leaf (preferably oak) with a layer of at least 10-15 cm.
When to close and when to open bushes?
There is no need to rush either. Light frosts (up to –10 ° С) are not dangerous for rhododendrons. But if the shelter is set too early, the root neck will begin to warp and the plant will die. Do not try to catch up to the first snow, which sometimes falls in October. You can scoop up the snow, but shelter in the optimal time - in mid-November.
It is also not necessary to open the bushes in the spring too early. May the March sun not tempt you. In March, the roots still doze in frozen ground and cannot absorb water. If you remove the shelter at this time, the delicate leaves of the evergreen rhododendrons will fall under the scorching rays - and "burn out", dry out and turn black. It is best to remove shelter from rhododendron bushes when the soil is completely thawed and warmed up a bit, and the weather on the selected day will be cloudy.
Propagated by seeds and vegetatively (layering, cuttings). Wild species are usually propagated by seed, and varieties are most often layering and cuttings.
Sowing seeds is carried out in the spring in cups or boxes, if there are a lot of seeds; small seeds are sown on the surface of the substrate or lightly sprinkled with clean, washed sand, abundantly watered with water, preferably soft (rain or from melted snow). Tap water is acidified by adding 3-4 g of oxalic acid per 10 l of water. Boxes are covered with glass or film to maintain high humidity. A mixture of peat and sand taken in equal amounts is suitable as a substrate. Before filling the boxes, the soil mixture is pickled with a strong solution of potassium permanganate.
At room temperature, seedlings appear after 3-4 weeks, in some species - after 18 days. When the first leaves of the seedlings appear, they should be transferred to a room with a lower temperature, about 8-12 ° C. Then the seedlings are less damaged by disease. In summer, boxes with shoots can be taken out into the garden and placed in a sheltered place, sufficiently lit, but not falling in direct sunlight. Rhododendron shoots are very small and delicate, and they should be watered through a pan, filling it with water until the entire substrate is saturated, after which excess water is drained.
Even a single drying leads to the death of young plants, but you should not arrange a swamp, which will lead to the death of the roots. For better development of seedlings, they must be illuminated with fluorescent lamps, placing them at a distance of 10-15 cm. The daylight hours should be 16-18 hours. On dark winter days, the backlight is best turned on in the morning. The first picking of seedlings is held in June. They are planted in boxes at a distance of 1.5 cm.
For winter, seedlings are returned to a warm room and kept at a temperature not exceeding 18 ° C. In February-March, they make a second pick, placing seedlings at a distance of 3-4 cm from each other. After 10 days, foliar top dressing with humate is given, and in summer - root - Kemira-universal, at the rate of 2 g per 2 liters of water. In the third year after sowing, seedlings can be planted in the nursery for growing. Already in 3-4 years of life, some rhododendrons grown from seeds (Daurian, Canadian, Japanese and others) enter the first flowering, which is most often weak and the first flowers are recommended to be removed faster so that the plant can retain strength for a more abundant and longer flowering in subsequent years.
Plants derived from rooted cuttings may bloom the following year. The substrate for rooting: peat and sand (1: 1), or sawdust and sand (3: 1), or a mixture of peat, perlite, sand (2: 2: 1). For cuttings, semi-lignified rhododendron cuttings are used. They are cut in the second half of June, the length of the cuttings is 5-8 cm, an oblique cut is made below. The lower leaves on the handle are removed, and the upper 2-3 are left completely.
Cuttings are treated with growth stimulators: indolylbutyric, indolylacetic, succinic acid in a concentration of 0.02% and hold in them for 12-16 hours, for hard-to-eliminate varieties, the concentration is 2-4%. Then the cuttings are immersed in the substrate obliquely at an angle of 30 ° C, pressed, watered with water and cover the box with glass or film. Cuttings root better at a substrate temperature of 24-26 ° C, and the air temperature is 2 degrees lower. A prerequisite is high humidity of the soil and the surrounding air cuttings. Dosing of cuttings (60 W for 4-5 hours per day) accelerates the rooting process.
Deciduous rhododendrons take root in 1.5 months, evergreens in 3-4.5 months. The rooting results depend on the species and variety. In rhododendron, Daurian roots form after 50 days. Rooting rate is 85%. Growing rooted cuttings is carried out in containers filled with a mixture of acid peat (2 parts) and pine needles (or decomposed pine bark) - 1 part.
Top dressing 2 weeks after transplanting into containers with 2% urea. Contain plants at a temperature of 8-12 ° C. In the spring they are planted in beds for growing or continue to be kept in containers for another 1-2 years until planting in a permanent place in the garden.
Decorative use of rhododendron
The most spectacular rhododendrons look like freely arranged groups. Landing is desirable to stir along the edges of lawns, near paths and paths. Since rhododendrons are moisture-loving plants, it is best to plant them near water bodies: ponds, pools, fountains, where in summer due to increased air humidity and moderate temperature the conditions are most favorable. Plants should be at least 3, and, for each should be allocated at least 1 square. m. In the absence of adult specimens, you can use thickened planting of young with the expectation that as they grow they will be sparse.
When creating groups, it is not recommended to mix deciduous and evergreen rhododendrons. If various species are planted nearby, then they need to be selected in height: in the center - the highest, at the edges - lower. Rhododendrons are very decorative next to conifers: spruce, pine, thuja, yew tree. Against a plain dark background, plants with bright colors are especially impressive. Evergreen trees and shrubs planted from the south, east, or west protect rhododendrons from cold winds, winter drying, and spring sunburn.
Since light penumbra is preferable for the normal growth and development of rhododendrons, they can be successfully planted between large, old trees or on the north side of buildings. The territory on the south side is not recommended for planting, especially for evergreen species. In this case, the plants are more susceptible to disease, their leaves turn yellow, growth and flowering weaken.
When placing rhododendrons in groups, you should strictly ensure that they are composed of such varieties and species that are in harmony in the color of the flowers. The most decorative neighborhood of plants with purple, pink and white color or with different contrasting shades. Rhododendrons with yellow and orange colors of flowers look amazingly good in the stands. Soft yellow tones effectively shade brighter.
Rhododendrons are beautiful not only in groups, but also in tapeworm plantings. They are especially good on ground grass, but it should be borne in mind that the decorative effect is maximum when using an adult (not younger than 10 years old), preferably a tall (1.5-2.0 m) plant, otherwise it will be "lost" on the lawn. Rhododendrons are also used to create hedges and rocky slides. For rock gardens, small-flowered low-growing varieties in combination with alpine species of herbaceous plants are most suitable.In such plantings, rhododendrons should be planted only in groups, which during flowering gives a greater effect.
Diseases and Pests of Rhododendron
Rhododendron bug - One of the most common pests of rhododendron. The length of the insect is 3.6 mm. Leaves small discolored spots on the leaves. On the underside, the bug lays brownish eggs that winter in leaf tissues. A new generation appears in the summer.
- Control measures: spraying with diazinon.
Mealybug - a small flat pest 2-4 mm in size. Males and females are very different from each other. Females are wingless and motionless. Males with one pair of wings, mobile. The pest gives 2-5 generations per year. It settles on leaf veins, young buds and young shoots of rhododendron, climbing into the cracks of the bark and buds, sucking out the cellular juice. With mass reproduction, it causes curvature of the leaves and death of plants.
- Control measures: spraying malathion 3-4 times a year.
Grooved weevil, or corrugated bevel - Adult beetle, 8-10 cm long, black (young individuals yellowish-brown), with yellow spots on thick leathery ribbed wings and a short nose. Adult individuals are inactive, but flying. They eat around the edges of leaves, sometimes eat away buds, buds and flowers, gnaw at the bark. Larvae 1-1.4 cm long, without legs, in appearance resemble larvae of the May beetle. They eat the bark at the root neck and the roots themselves, leading the plant to death. Weevil lays eggs throughout the summer. Larvae live and winter in the soil, and pupae form in spring. Beetles appear in May-June.
- Control measures: plants are watered with 0.2-0.3% emulsion of malathion. At night, during the period of activity of adults, they pollinate with 0.3% malathion emulsion. In June-August, 0.1-0.15% solution of bazudine is sprayed to soak the soil or layer of mulch. Good results are given by spraying with diazinon and furadan.
Spider mite - insect up to 0.5 mm long, red, yellow or reddish-green color. Adults with 8 legs, very mobile. Appears on the underside of the sheet, covering it with a thin web stretched in all directions. It feeds on the juice of leaves, which become brownish-gray and fall off.
- Control measures: spraying with agravertine, diazinon.
Khrushchik asian garden - wide polyphage. Strongly harms plants, eats holes of irregular shape in young leaves, often affects the entire leaf, leaving only its veins. Larvae damage the roots and stems of rhododendron.
- Control measures: spraying with diazinon.
Slime plowed - damages more often leaves of young plants, gnawing through openings. It feeds mainly at night or on cloudy days. It is dangerous because in a short time it can destroy young plants.
- Control measures: watering with 0.8% TMTD solution, collecting adults.
Black thrips - It is mainly a greenhouse pest, but has recently been found in open ground. Adults are small (1-1.5 mm), black. Larvae are yellow, smaller than adult insects. Pests feed on the leaves, resulting in gray holes on the upper side of the sheet, and black holes on the lower side. The leaves turn silver gray, turn yellow and fall off. In addition, thrips causes ugliness of flowers and a strong lag in the growth of shoots.
- Control measures: spraying with 0.2-0.3% nicotine solution or 0.2% malathion emulsion.
Small-winged moth miner. Young caterpillars break through the tunnel-like passages, eat away the leaf parenchyma, staining its surface, twisting the edges of the sheet into a pupation tube. Damaged leaves dry out, crumble and fall off.
- Control measures: plants are sprayed or fumigated with sulfur.
Mixed chlorosis. Yellow spots appear at the ends and edges of the leaves. They can arise due to a lack of nutrients (nitrogen, potassium), which are relatively easily washed out of the soil during irrigation. Another reason can be stagnation of water at the roots. Typically, chlorosis appears brighter in the second half of July or in August, when the leaves reach normal sizes. Light yellow and intensely yellow spots between the leaf veins occur when there is a lack of iron or magnesium in the soil, as well as when the root system is compacted, or if the soil reaction is shifted to the alkaline side. Sometimes this is caused by a lack of calcium (in Caroline rhododendron).
- Control measures: foliar top dressing with ferrous sulfate (7.5 g / l), magnesium sulfate (6.5 g / l).
The consequence of the lack of nutrients in the soil are red spots along the veins, coagulation of leaves in a tubule, drying out of branches. With nitrogen starvation, the leaves of rhododendron become smaller, growth is less, flowering is weak, in evergreen plants, leaves on the shoots last only 2, and not 3-5 years, as in nature or with normal care of plants in culture.
- Control measures: top dressing with ammonium sulfate or nitrate, or potassium nitrate.
Necrosis - the death of the main vein of the leaf, in which the upper side of the leaf turns brown. It can cause a sharp drop in air and soil temperature (especially in insufficiently winter-hardy varieties of rhododendron).
The condition of plants can be affected by strong winds, drought, high salt content in the soil, poor aeration of the substrate, mechanical damage to the roots, lack or, on the contrary, excess nutrients in the soil. In each case, it is necessary to identify the cause and eliminate it.