Rhododendron

In terms of the luxury of flowering and the brightness of the colors, the rhododendron is undoubtedly the king of flowering shrubs, which has a truly hypnotic effect. In many species, delicate white, yellow, pink, lilac, salmon, red, purple flowers are collected in 5 – 20 pieces in large inflorescences: each is a miniature bunch. They stay fresh for a long time in a vase.

This is a very ancient botanical genus. Paleobotanists have established that the ancestors of modern rhododendrons grew on Earth about 50 million years ago! In nature, rhododendrons are common in temperate regions of Southeast Asia and Malaysia with mild winters, where there is a lot of rainfall. These are coastal zones, the lower and middle belt of mountains. In the East, they were introduced into culture, in Japan, rhododendrons were planted near temples already at the beginning of the 1th century, since then they have been bred in gardens around the world (4, XNUMX).

Types and varieties of rhododendron

The genus Rhododendron is a member of the Heather family (Ericaceae). It has about 1300 species and more than 12 varieties. About 000 species are grown in Our Country. 

Rhododendron Daur 

Rhododendron Daur (Rhododendron dauricum) is a deciduous, highly branching spreading shrub up to 2 m high, originally from the Sayan Mountains, Transbaikalia and the Far East, where it is called wild rosemary. 

The leaves are olive, oval, up to 4 cm long and about 1 cm wide. It blooms in the second half of April, before the leaves appear, and blooms until mid-May. The flowers are funnel-shaped, about 4 cm in diameter, pink in different shades, sometimes white, fragrant, bloom at the same time. 

Quite winter-hardy (down to -30 ° C), but in winters with frequent thaws, flower buds may suffer. Long-lived – lives and blooms annually for 50 years or more (2).

It has quite frost-resistant varieties that can be successfully grown in central Our Country. And the most popular of them belong to the series April (April) – these are early-flowering varieties.

April Jam (April Gem). The bush is round, by the age of 10 its height is about 0,7 m, diameter 0,9 m. The leaves are elliptical, dark olive. The flowers are white, broadly funnel-shaped, 3–5 cm in diameter, double, fragrant. Flowering is plentiful. Winter hardiness – up to -32 ° С.

April Reign (April Reign). The height of the bush is about 1 m. The flowers are double, pink, blooms in mid-April. Winter hardiness – up to -30 ° С.

April snow (April Snow). Bush about 0,8 m high. Flowering is very plentiful. Flowers are white. Tolerates frost down to -28 °C. 

Also a very popular group of varieties Rhododendron P.J.M. Group with pink and light purple flowers, bred as a result of crossing Daurian and Carolina rhododendrons: Elite, Northern Starburst, Checkmate, P. J. Mezitt, Lavender, Princess Susan, Regal.

Caucasian rhododendron

Caucasian rhododendron (Rhododendron caucasicum) is an evergreen shrub 1–1,5 m high and up to 3 m in diameter. It occurs naturally in the subalpine belt of the mountains of the Central and Western Caucasus.

The leaves are oblong-oval, up to 12 cm long, dark green, smooth above, with rusty-brown pubescence below. The flowers are wide-funnel-shaped, cream or almost white with green specks in the center, collected in inflorescences of 5-10 pieces. Blooms in June until new leaves appear. Winter hardiness – up to -28 ° C, varieties are also winter hardy (2).

Among the varieties, 4 of the most popular can be noted.

Pictum (Pictum). Bush up to 0,5 m high with large pink flowers.

Cunningham White (Cunningham’s White). A variety of hybrid origin from crossing with the Pontian rhododendron with large pure white flowers. 

Christmas Chir (Christmas Cheers). garden form. The flowers are white with a slightly pinkish edge of the petals.

Chevalier Felix de Sauvage (Chevalier Felix de Sauvage). garden form. Intense bright pink flowers. Blooms in May.

Rhododendron Katevbinsky

Rhododendron Katevbinsky (Rhododendron catawbiense) is an evergreen, fast-growing shrub 2–3 m high and up to 6 m in diameter, native to North America. 

The leaves are elliptical, up to 15 cm long, dark green and shiny above, dull grayish green below. The flowers are lilac or purple, up to 6 cm in diameter, collected in inflorescences of 15 – 20 pieces. Blooms profusely in May June for a month. Winter-hardy, successfully winters in the middle lane and even to the north (2). 

Within this species, there are also interesting varieties.

Katevbinsky large-flowered (Catawbiense grandiflorum). The most common and reliable variety of Katevbinsky rhododendron. It is distinguished by resistance to frost down to -32 ° C and rapid growth. The flowers are purple-pink.

Pink Purple Dream (Pink Purple Dream). A team of sorts Catawbiense Grandiflorum. The bush is dense, compact, by 10 years the height is about 1,2 m and the diameter is up to 1,8 m. Easily tolerates pruning, suitable for hedges. Leaves 10-12 cm long, glossy dark green. The flowers are light purple with yellow-brown strokes on the upper petal. Flowering is plentiful, in late May – early June. Frost resistance – up to -30 ° C.

English Roseum (English Roseum). Hardy variety of hybrid origin. Withstands direct sunlight, frost and showers during flowering. The flowers are funnel-shaped, lilac-pink, with orange freckles, collected in domed inflorescences of 8 – 10 pieces.

New Zembla (Nova Zembla). The bush reaches 2,5 m in height and 2 m in diameter. The flowers are bright pink with maroon spots. Frost resistance – up to -30 ° C.

Other winter-hardy varieties: Burso, Roseum Elegance, Azurro, album, Purpureum, Homebush.

Rhododendron of Schlippenbach

Rhododendron of Schlippenbach (Rhododendron schlippenbachii) is one of the most beautiful deciduous rhododendrons. Bush up to 3 m high. Leaves obovate, up to 10 cm long, dark green, purple in autumn. Flowers 5-8 cm in diameter, pale pink with purple dots. In an inflorescence up to 6 flowers and they bloom at the same time.

Blooms from late April – early May to June. It is winter-hardy, but needs shelter with lutrasil during spring frosts so that the flower buds do not die.

There are garden forms with different flower colors (2).

Rhododendron Japanese

Rhododendron Japanese (Rhododendron japonicum) is a deciduous shrub up to 2 m high with a wide spreading crown native to the Japanese Islands. It grows slowly – the annual growth is not more than 10 cm. The flowers are funnel-shaped, with a diameter of 6 – 8 cm, yellow, salmon, red with a yellow-orange spot, bloom simultaneously with thin green leaves. All Japanese rhododendrons have a delicate aroma. It blooms in May – June, abundantly and for a long time. Enough winter-hardy in the middle lane. Light-loving (2, 4).

This species has 2 interesting garden forms.

Salmon. Bush up to 2 m high. The leaves are oblong-oval, 10 – 12 cm long, bright green, fiery red in autumn. The flowers are red with a salmon shade, up to 7 cm in diameter, collected in inflorescences of 6 – 12 pieces. Blooms in May for 3 weeks.

Cream. Bush height 1,2 – 2 m, Leaves up to 10 cm long, dark green, lemon yellow in autumn. The flowers are creamy with a bright yellow center, collected in inflorescences of 6 – 12 pieces.

And the Japanese rhododendron has no less interesting varieties.

Grandmother (Babushka). Miniature variety. Bush height and diameter up to 50 cm. The leaves are dark green, shiny, yellow in autumn. The flowers are semi-double, carmine-pink.

Schneeperl (Schneeperle). Dwarf variety, 10-year-old bush reaches 35 – 45 cm in height and 55 – 60 cm in diameter. The leaves are dark green. Flowers with a diameter of 4 – 5 cm, double, boiled white. 

White Prince (White Prince). Bush up to 2 m in height. Leaves up to 10 cm long, oblong-oval green. Flowers with a diameter of 6 – 8 cm, white or with a pale pink center. 

Rhododendron hybrid

Rhododendron hybrid (Rhododendron hybrida). This includes thousands of breeding varieties registered by the Royal Horticultural Society of Great Britain.

Here are just a few of the most fashionable.

Sept. Мишель / Mikkeli (St. Michel / Mikkeli). The hardiest of Finnish evergreen rhododendron varieties. Bushes 1,5 – 2,0 m high and 1,2 – 1,5 m in diameter, dense, compact, densely branched. Young shoots are pubescent. The leaves are large, dark green, dense, create an excellent background for flowers. The buds are pink. The flowers are white at first with a pink blush, but quickly become pure white. On the upper petal is a light green speck. 

Smoke Purple (Pushy Purple). A hybrid variety of evergreen rhododendron, easy to care for and hardy. Handles pruning well. Suitable for growing in containers.

The bush is compact, slowly growing by the age of 10 reaches about 1 m in height and up to 1,5 m in diameter. 

The leaves are dark green, leathery, elliptical. The buds are dark purple. Flowers 8-9 cm in diameter, funnel-shaped, creamy white with a narrow contrasting dark purple border and a yellow spot on the upper petal. The pink stamens protrude beautifully from the center of the flower. The inflorescence contains about 20 flowers. They are good for boutonnieres and mini bouquets (about 10 cm high, up to 15 cm in diameter). Blooms profusely in June. Frost resistance – up to -22 ° C, for the winter he needs shelter. 

neon kiss (Neon Kiss). Hardy evergreen variety with exceptionally bright and expressive neon raspberry red flowers. Blooms in May annually and profusely. The bush is dense, by 10 years the height is about 1,2 m. The leaves are dark green. Frost resistance – up to -28 ° С. Can be grown in containers.

Georges Sand (Georg Sand). Classic variety. Evergreen low dense bush of spherical shape. It grows slowly, after 10 years the height and diameter of the bush is up to 0,7 m. The leaves are lanceolate, leathery, dark green, shiny. The buds are pink. Flowers with a diameter of 5 – 6 cm, yellow with a clear speck on the upper petal, up to 12 pieces in an inflorescence. Blooms profusely in early May. Frost resistance – up to -23 ° C, needs shelter for the winter.

Krakovets (Krakovec). Evergreen compact shrub, by the age of 10, the height and diameter of the bush is 1,0 – 1,4 m. The leaves are dense, leathery, dark green, semi-glossy. Flowers 5-6 cm in diameter, bright to dark red with a white center. Petals with a wavy edge. Blooms in late May – early June. Frost resistance – up to -20 ° С.

Rhododendron Care

There are already a lot of rhododendrons in the gardens of central Our Country, but not every grower succeeds. Their wide distribution is hindered by frosty winters, insufficient precipitation in summer, and dry air in May-July. But there is a plus – rhododendrons put up with the close occurrence of groundwater.

If you decide to plant rhododendrons, be prepared to provide shelter for the winter, abundant watering and sprinkling plants in drought (3, 5).

Place

For rhododendrons, choose a warm place, protected from the winds and the midday sun, ideally on the east side of the house or fence. They do not like direct sunlight, as leaf burns and burnout of flowers are possible. Penumbra is fine, but

even resistant Finnish varieties WFP – Tigerstedt, Mikkeli, The Hague and others should be planted not just in partial shade, but where it is in the middle of the day, and not only in the warm season, but also in winter – from coniferous plants or from high buildings. The leaves must be protected from the spring sun!

Deciduous species can grow in an open area – yellow rhododendron, Japanese rhododendron and Kamchatka rhododendron.

The distance between the bushes for low-growing forms is 0,5 m, medium-sized -1 – 1,5 m, high – 2 – 3 m.

Ground

Plants are most suitable gravelly slightly acidic soil (in no case limestone). They also dislike nitrogen-rich soils.

Landing

The planting hole is dug 3 times wider and 2 times deeper than the size of the root ball of the seedling. On clay soils, drainage is required – a layer of broken bricks.

Fill the pit with a mixture of leafy soil, peat and coniferous litter (3:2:1), adding 70 g of nitrophoska to it. It is good to mix sphagnum moss and pine bark composted for 3-4 years. The optimum acidity of the soil (pH) is 4,5 – 5,5.

If varietal seedlings of rhododendrons on the INKARHO rootstock, the plants do not need acidic soil, any loose and rich in organic soil will do.

You can plant rhododendrons in containers all season, but not in late autumn and not during flowering. Before planting, the root ball is soaked in a bucket of water for 1 to 2 hours, and in order not to fall apart, it must be wrapped with burlap. 

Planted bushes are plentifully watered and topped up with earth. The root neck after soil subsidence should be strictly at ground level. When deepened, rhododendrons bloom poorly and may die. Before planting and immediately after it, the plants are not pruned.

Watering

Rhododendrons love moist soil and humid air and at the same time cannot stand flooding. In dry and hot weather, plants are watered 3 times a week so that the soil is saturated to a depth of at least 30 cm, this requires 10-12 liters of water per bush. If the water is hard (from a well), it is acidified with citric or oxalic acid (1 teaspoon per 10 liters of water). 

The air humidity around the plants is maintained by regular spraying or sprinkling.

fertilizers

For rhododendrons, acidic mineral fertilizers are preferred:

• nitrogenous – ammonium sulfate, ammonium chloride, ammonium nitrate, urea, ammonium bicarbonate;
• phosphorus – superphosphate;
• potassium – potassium sulfate;
• complex – ammophos. 

An ideal mixture of ammonium sulphate, superphosphate and potassium sulphate (2:1:1,5). It is added at the rate of 40 g (2 matchboxes) per 1 sq. m. In no case should fertilizers containing chlorine (potassium chloride, calcium, magnesium) be used. 

Special fertilizers for rhododendrons (GumiMix, etc.) have proven themselves well, as well as Mycorrhiza universal fertilizer containing symbiont mushrooms that help weak rhododendron roots absorb nutrients faster. 

Feeding

During the season, rhododendrons need several top dressings:

• in early spring, and at the beginning of shoot growth, dry fertilizer is scattered over the mulch (a mixture of ammonium sulfate, superphosphate and potassium sulfate in a ratio of 2: 1: 1,5) and watered abundantly;
• during the period of budding and flowering – once a week with a solution of complex mineral fertilizer Aquarin (1 g per 20 l of water);
• after flowering – infusion of manure (0,5 l per bucket of water), the norm is 1 bucket per 2 bushes. 

At the end of summer, fertilizers are not applied – by this time, vital processes are already slowing down in plants.

Rhododendrons have a superficial root system, and they react painfully to drying out of the soil and loosening. Therefore, near-stem circles must be mulched with peat, sawdust, wood chips, needles, a layer of about 10 cm. The area around the stem is left free. Mulch keeps the soil temperature constant and protects the roots from frost.

Trimming

In the spring, dry branches are cut out, the crown is thinned out, and the shoots are shortened, forming a neat bush shape.

Faded inflorescences are immediately plucked out – if this is not done, the plant will consume nutrients to form seeds, to the detriment of laying new flower buds.

As the branches age, they become bare at the bottom, in this case the oldest ones are cut out, and a few more branches are shortened at a distance of 30–40 cm above the ground (1, 4).

Shelter for the winter

In late autumn, rhododendrons need abundant moisture-charging watering. In winter, it is difficult for plants to resist not only frost, but also temperature changes – from cold to thaw and vice versa. The cold, withering wind is also dangerous, to protect against which the bushes are tied with twine and wrapped in dense lutrasil. 

When freezing, buds turn black in deciduous rhododendrons, and leaves die off in evergreens. Sometimes cracks appear on the bark, they must be immediately covered with RanNet paste or other similar means to prevent infection.

Evergreen rhododendrons are covered with spruce branches for the first 3-4 years after planting for the winter. Older undersized bushes can be completely covered with fallen leaves, best of all oak.

In deciduous rhododendrons, the branches are bent to the ground so that they are completely under the snow. Do this as soon as the topsoil begins to freeze.

Shelter is removed in late March – early April, when the average daily air temperature steadily exceeds 0 ° C. Light lutrasil on evergreen rhododendrons can be left for a short time to prevent sunburn, in which dry brown spots appear on the leaves (3, 5).

Reproduction of rhododendron

Propagating rhododendrons is very difficult, all methods are only suitable for gardeners with serious intentions.

Seeds. Rhododendron seeds do not need stratification and are sown in the spring on a seed bed in the open field. Can be sown indoors and grown like seedlings for 2 years, which is labor intensive and needs to be monitored. 

The substrate for sowing seeds is prepared from high-moor peat, washed sand and fallen needles (2: 1: 1). Shoots appear after about 1 month. As they grow, the seedlings are planted several times using a soil mixture for heathers – Compo Sana, Green Line, etc. For the 4th year they can be planted in a permanent place. 

Cuttings. Rhododendron cuttings will take root poorly, slowly, only under favorable conditions and the use of root stimulants. 

Semi-woody cuttings 6-10 cm long are cut in the third decade of June. Before planting in a greenhouse, the lower leaves are removed from the cuttings, the sections are updated and dusted with Kornevin, Kornerostom etc. As a substrate, a mixture of sand with crushed high-moor peat (1: 1) is used. 

A prerequisite for rooting is high soil and air humidity, as well as good lighting and ventilation. Rooted cuttings are grown in containers. They are periodically fed with a solution of fast-acting complex fertilizers – Fertika Lux, Aquarin, etc. Next spring they can be planted in a seed bed or continue growing in a container for another 1 to 2 years.   

Layers. This method is suitable when you need to get only a few new plants. The performance is standard, as for any shrub, but rooted cuttings are separated from the mother plant only for 2 years. 

Air layers. In some ways, the propagation of rhododendrons by air layering is even easier. On a strong young shoot, a bark ring 1–2 cm wide is removed, while it is important not to damage the wood. This place is sprayed with a solution of heteroauxin (250 mg / l), wrapped with moistened sphagnum moss, on top with a strip of polyethylene film, which is tied to a branch from above and below. Several holes are pierced in the film for ventilation and spraying from a spray bottle. After 1 – 1,5 months, when the roots appear, the cuttings are cut off, planted in a pot and grown for 1 – 2 years.     

other methods. In nurseries, rhododendrons are propagated by winter grafting. As rootstocks, 3-year-old seedlings of Kovtebinsky, yellow, Japanese rhododendrons are used.

Rhododendron bushes can be divided, but in our climate this is rarely resorted to. If the rhododendron has taken root, grown and pleases, it is better not to disturb it.

Rhododendron diseases

With a lack of iron and (or) magnesium in the soil, rhododendrons develop chlorosis, on soils close to neutral, these nutrients are often inaccessible to plants. 

At the first symptoms of chlorosis, rhododendrons should be watered with solutions of magnesium sulfate and iron sulfate – 30 g per 10 liters of warm acidified citric or oxalic acid 10 g per 10 liters of water. The color of the leaves is restored in about a month.

For prevention root rot Trichodermin, Trichocin, Gliocladin (6) are added to the soil with which the planting pit is filled – according to the instructions and in the future I use these preparations every spring.

Против rust plants are treated with topaz, from spotting on the leaves – copper-containing preparations.

Pests of rhododendron

The beautiful rhododendron has a lot of enemies – aphids, thrips, spider mites, narrow-winged mining moth, furrowed weevil, mealybug. There are also personalized ones – a rhododendron bug and a rhododendron fly. 

Rhododendron bug. It lays its eggs on the underside of the leaves and leaves dark “tar” excrement there. When insects reproduce, the plant looks messy. 

Spraying with insecticides Kinmiks and Decis (2 ml per 10 liters of water) with the addition of an adhesive (Liposam) to the solution will help. Adherents of organic gardening can use the infusion of tobacco dust with the addition of laundry soap.

Mealybug. Grayish white, as if floured, hairy insects less than 1 cm long suck the juice from plants, causing stems and leaves to twist. 

Fortunately, this dangerous pest is clearly visible, when it is detected, the plants are treated 3-5 times, alternating the Karbofos emulsion (0,4%) and the green soap solution.

Furrowed weevil. Adult insects feed on leaves and buds of evergreen rhododendrons. Dark gray beetles up to 1 cm long eat leaf blades along the edges. The larvae living in the soil damage the roots, the plant wilts and may die. 

To combat the pest, the soil is watered with 0,3 – 0,5% Karbofs emulsion. Plants are sprayed with Decis, Actellik, Spark (6).

Narrow-winged mining moth. Its caterpillars gnaw out passages in the tissues of the rhododendron leaf, and when pupating, twist the leaves into a tube. Damaged leaves dry up and fall off. 

Plants are somewhat sprayed with sulfur-containing preparations at intervals of 7 to 10 days.

Popular questions and answers

We talked about growing rhododendrons with agronomist-gardener Irina Belozerova.

Sources of

1. Alexandrova M.S. Rhododendrons // M .: Fiton +, 2001
2. Alexandrova M.S. Caring for rhododendrons // M .: Kladez-Buks, 2008
3. Voronina S.I. Rhododendrons for the North-West // St. Petersburg: House of Garden Literature, 2018
4. Kondratovich R. Rhododendrons // Riga, 1981
5. Rupasova Zh., Volodko I., Goncharova L. Rhododendrons in Belarus // Minsk. Lamber, 2005.
6. State catalog of pesticides and agrochemicals approved for use on the territory of the Federation as of July 6, 2021 // Ministry of Agriculture of the Federation https://mcx.gov.ru/ministry/departments/departament-rastenievodstva-mekhanizatsii-khimizatsii- i-zashchity-rasteniy/industry-information/info-gosudarstvennaya-usluga-po-gosudarstvennoy-registratsii-pestitsidov-i-agrokhimikatov/