6 May 2020

How To Grow Rhododendrons — Useful tips and landscaping ideas

By Christopher Brickell

What is rhododendron?

beautiful rhododendron

In this article we tell you how to grow Rhododendrons and share with you Rhododendrons landscaping design ideas. Rhododendron is a member of the Ericaceae family. This genus is represented by shrubs and trees, which are deciduous, semi-leaved and evergreen.  According to various sources, this genus unites 800-1300 species, including azaleas, which are very popular among flower growers.

The name of this plant includes 2 words: “rhodon”, which translates as “rose” and “dendron” – meaning “tree”. For this reason, rhododendron means “tree with roses” or “rose tree”. The fact is that rhododendron flowers are externally similar to roses. In wild conditions, rhododendrons are most common in the northern hemisphere (southern China, Himalayas, South-East Asia, Japan and North America).

They prefer to grow in the coastal zone of seas, rivers and oceans, on northern mountain slopes and in the shade of undergrowth. Some species reach a height of 0.3 m, while others are reindeerable shrubs. Flowers of different species of this genus differ not only in color, but also in shape and size.

Features of rhododendron

how to grow rhododendron
The garden rhododendron is a shrub. Different species may vary in size and shape of leaf plates, which are two-year, annual and perennial, petiole or sessile, serrated or whole-edged, obovate or ovoid. It’s not a surprpize, if you want to grow rhododendrons. This plant is relatively popular in all countries of the world because of its ornamental foliage, as well as beautiful flowers. Flowers can be painted pink, purple, white, red or purple. Flower shape directly depends on the type and variety of plant and can be funnel-shaped, tubular, bell-shaped or wheel-shaped. Some flowers have a pleasant odour.

How to grow Rhododendrons: planting and care

rhododendron in a pot

Choice of time and place to grow Rhododendrons

Time

It is recommended to cultivate only those rhododendron species that are highly frost-resistant. The plant can be planted in open soil from April to the second half of May, and in September-November. Experienced gardeners plant the rhododendron throughout the growing period, except for the flowering time of this shrub, and should not do so for 7-15 days after flowering.

grow rhododendron

Place

For planting choose a shaded area on the north side of your house. The soil should be well drained, loose, contain plenty of humus and be acidic. If the depth of groundwater in the area is less than 100 cm, you will need to make an elevated bed for planting this shrub. You can grow rhododendrons next to trees such as oak, pine and larch as their root system goes deeper. We do not recommended to plant this shrub next to chestnut, maple, elm, lime, alder, willow and poplar trees because their root systems are at the same depth as the rhododendron, so the latter will lack the necessary nutrients and moisture.

If you have to grow rhododendrons next to one of the trees listed, you will need to protect the edges of the planting hole by digging into the soil slate, roofing felt or polyethylene. The best neighbours for this plant are the pear and apple tree.

How to plant rhododendrons

If you decided to grow rhododendrons, here is the instruction how to plant it.

how to plant rhododendron

  • Prepare a hole for planting, so that its depth should be about 0.4 m and its diameter about 0.6 m.
  • Pour a soil mixture consisting of 3.5 buckets of loam (can be replaced with a pair of clay buckets) and 8 buckets of horse peat into it.
  • Mix it thoroughly.
  • Thoroughly compact the soil mixture sprinkled into the pit.
  • Then make a hole in it, the size of which should be equal to the size of the root coma of the plant.
  • Immediately before planting, immerse the seedling in a container filled with water.
  • Remove it only after the air bubbles stops coming out onto the water surface.
  • After that, place the root system in a hole, which is filled with soil mixture, it must be very well compacted, so that there are no voids.
  • The planted seedling should have the root neck at the same level as the surface of the area.
  • The plants that have been planted need plenty of water.
  • If you planted the rhododendron in dry soil, you need to water it generously so that the ground is 20 centimetres wet.
  • Then coer the surface of the fitting circle with a layer of mulch (oak leaves, pine needles, peat or moss), with a thickness of 50-60 mm.
  • If a seedling has a large number of buds, cut off a part of it, the forces of the plant will be directed to rooting rather than to lush flowering.

How to care for Rhododendron

rhododendron bush
If you plan to grow rhododendrons, remember this plant needs good care. It needs to be sprayed, irrigated, fed, weededed, shaped and protected from pests and diseases in good time.

The level of atmospheric and ground humidity is especially important for this crop compared to other garden plants, especially during budding and flowering. It is very important to water Rhododendron correctly because it has a significant influence on the laying of future season’s flower buds.

  • Water the plant with soft water only (permanent or rainwater). Some gardeners soften and acidify the water very easily, for this they mix it with ripe peat 24 hours before watering.
  • From the condition of the leaf plates you can determine how often you should water the shrub.
  • Water the plant if the foliage becomes matte and loses its turgor.
  • During irrigation, the ground should be soaked to a depth of between 20 and 30 centimetres.
  • When watering, it is also very important that no liquid stagnates in the ground, as the root system reacts extremely negatively. When the water stagnates, the rhododendron behaves in the same way as when there is not enough moisture.
  • To avoid overwetting, you need to water the shrubs in the same way as you always do in a dry, hot period, but you need to moisten them from the sprayer quite often using soft water.

Autumn care

If you grow rhododendrons , you need to know how to care for it in autumn. If there is a drought in autumn, rhododendron will need regular abundant watering, so under 1 bush you should pour out 10-12 liters of water. If there is systematic rainfall in autumn, there is no need to water such plants. In November you should insulate the root system of the shrub, for this purpose, the surface of the nozzle wheel should be ground with a layer of peat.

Winter season

If you grow rhododendrons , you need to know how to care for it in winter. If rhododendron is grown in middle latitudes, the bushes should be insulated after the first frosts. For this purpose, pine or spruce branches are inserted between the branches of the plant, and the shrub itself is slightly tightened with twine. Then it should be covered with sacking. Remove the sacks from the plants at the beginning of spring after the snow has melted and choose a cloudy day for this. If rhododendron is cultivated in a region with a fairly warm climate, it does not need shelter for the winter.

 

How to trim rhododendron

how to trim rhododendron
Since bushes most often have the right shape from nature, there is no need for strong forming trimming. As a rule, the plant needs to be cut back if the shrub is too tall, or if rejuvenating trimming is necessary or if stems were damaged by frost.

What are the rules for pruning adult shrubs?

When you decide to grow rhododendron, you need to learn some trimming rules.

  • Trim the stems in spring and cut them  in time before the falconstitution begins.
  • Smear the cuttings on branches that are between 20 and 40 mm thick with a garden brew. The awakening of sleeping buds on the stems begins after 4 weeks, at the same time as the renewal process, which lasts throughout the year.
  • If the shrub is very badly damaged by frost or old, shorten it to 0.3-0.4 metres, cut one half of the shrub in the first year and cut the other half the next year.

Such plants have one very important feature. One year, their flowering is characterized by its abundance, while next year it bears blooms much less. However, you can correct this periodicity, if you grow rhododendrons. For this purpose, after the flowering is over it is necessary to break out all the blossoming inflorescences. In this case, the shrub will direct all the saved strength and nutrients to the laying of flowering buds of the next season.

How to feed rhododendron

Even the bushes planted in the current season need feeding. For the first time in the season, feed the plant is at the beginning of the spring period, and for the last time at the end of July, when the plant blooms and young stems begin to grow. Specialists recommend that you use liquid fertiliser, which should include hornmeal and half-cow manure, as a fertiliser for the crop. To prepare such fertilizer, combine manure with water at a ratio of 1:15, then it should stand for a few days, only then you can feed the bushes. Before feeding rhododendron, you should water it well.

If you grow rhododendrons, remember, such plants need acidic soil, so the choice of mineral fertiliser should not disturb the reaction of the environment. Thus, it is recommended to use superphosphate, phosphorus, nitrogen and potassium sulphate, ammonium sulphate, calcium sulphate and magnesium sulphate, while taking them in weak concentrations (1,2:1000). And the potassium fertilizer solution should be even weaker.

Recommended fertilizer application mode:

  • At the beginning of spring, apply either organics or mineral fertilizers containing nitrogen, and take 50 grams of magnesium sulphide and the same amount of ammonium sulphide per 1 square meter of the site;
  • In the first days of June, when the plant blooms, bring 20 grams of potassium sulphide and superphosphate, as well as 40 grams of ammonium sulphide on 1 square meter of the site;
  • Feed rhododendron with 20 grams of potassium sulphide and superphosphate per 1 square metre for the third time in July.

Diseases and pests

rhododendron desease

Most often, when you grow rhododendrons, they are inhabited by powdery worms, shields, spider mites, bedbugs, weevils, rhododendron flies, as well as slugs and snails.

  • If gastropods occure  on bushes, gather them manually, and for preventive purposes the plant is sprayed with a solution of fungicide preparation Tiram or TMTD (8%).
  • If rhododendron bedbugs, spider mites or weevils have settled on rhododendron, spray it with Diazinon.
  • In this case of weevils, treat not only the bush but also the ground surface near it.
  • In order to get rid of other pests, use Carbofos, and follow the steps given in the instructions.

The most common diseases of this plant are fungal diseases such as cancer, rust, chlorosis or leaf spotting. Most often, such diseases develop as a result of insufficient aeration of the root system.

  • If rhododendron is affected by rust,  spray it with copper-containing preparations, for example, a Bordeaux mixture.
  • In case of chlorosis, the bush changes its colour to yellow, pour iron chelate into the water for irrigation.
  • If rhododendron has cancer, the affected stems should either be trimmed to a healthy tissue or removed altogether.
  • For prevention, you should spray the bushes with a Bordeaux mixture at the beginning of spring and in deep autumn.

How to spread rhododendron

If you grow rhododendron, you need lo learn how to spread it.

The plant can be spread by seeds or by vegetative methods such as layering, grafting, shrub dividing and cutting. The quickest and easiest way to spread such a plant is by layering.

Seeds

rhododendron seeds

  • For sowing seeds, use flat bowls and fill them with moistened peat or heather soil mixed with sand (3:1).
  • Once the seeds have been sown, sprinkled them with sand from above.
  • Cover the containers must be with glass from above and then put it to a well lit place.
  • Water the seeds in good time, ventilate it every day and remove condensation from the glass surface regularly.

As a rule, the first seedlings appear after 30 days. When the seedlings form a pair of these plates, you need to plant them more freely, using the scheme of 2×3 cm.  Seedlings in the first year of life should be grown in a cool greenhouse. In the second year, the seedlings should be transplanted into open soil on training beds with garden land mixed with a little peat and sand. Such seedlings have relatively slow growth. Their first flowering can be seen only in 6-8 years.

Cutting

rhododendron spread

When you decide to grow rhododendrons, you also need to know about a cuttting method.

Cutting is also a rather difficult way to spread rhododendron. Semi-tree stems are used to prepare the cuttings. The length of cuttings can vary from 50 to 80 mm.

  • Tear the lower sheet plates with  cuttings.
  • In this case, immerse the lower cuts  in a mixture that stimulates the growth of roots (eg, heteroaxine), for 12-16 hours.
  • For rooting, place the cuttings in a substrate consisting of sand and peat (1:3).
  • Then cover the container with a transparent dome.

The rooting of the cuttings is a long and difficult process. Thus, the rooting of evergreen species lasts from 3 to 4.5 months, and foliage – 6 weeks. For further growth cuttings are planted in boxes filled with a substrate consisting of pine needles and peat (1:2). During the winter period the cuttings should be in a well lit and cool (8 to 12 degrees) room. When spring comes, the crate of cuttings should be buried in the garden. There, they will grow for another 1 or 2 years.

Layering


The easiest and most natural method of reproduction of this crop is digging up the branches.

  • In springtime you should choose a low-growth young flexible shoot, it should be bent and placed in a prepared groove that should be at least 15 centimeters deep.
  • The middle part of the stem should be fixed in the groove by pinning it down.
  • Then the groove should be filled with garden soil connected to the peat.
  • The remaining top of the stalk on the surface should be tied to a vertically installed spike.
  • When watering the shrub itself, do not forget to moisten the outlet.
  • In autumn or next spring, the branch pipe should be cut off from the parent plant and placed permanently. This method is ideal for multiplying the deciduous rhododendron.

Types and varieties of rhododendrons with pictures and names

There are a very large number of rhododendron species. If you want to grow rhododendrons, below you will find the species that are cultivated by gardeners as well as the most popular garden varieties.

  • Rhododendron dahuricum.

how to grow rhododendrons dahuricum
Under natural conditions, these rhododendrons grow on rocks and in coniferous forests of North-Eastern China, Eastern Siberia, Primorsky Krai, Korea and Northern Mongolia.

  • Rhododendron adamsii


Theseevergreen rhododendrons grow on stony slopes and in the mountain forests of the Far East and the northeastern foothills of Tibet.

  • Rhododendron japonicum

how to grow rhododendron dahuricum
Homeland of this species is Japan, or rather Honshu Island, where rhododendrons grow on sunny mountains. This species is one of the most beautiful deciduous rhododendrons.

  • Rhododendron caucasicum

how to grow Rhododendrons caucasicum
This species can be found in nature in the Caucasus. This not very high shrub is evergreen. Decorative shapes:

  • pink and white – flowering starts earlier than the main species;
  • glossy – the color of flowers is dark pink;
  • golden-yellow – there is a pale green nettle on the surface of yellow flowers;
  • straw yellow, light red spots on the surface of yellow flowers.

 

  • Hybrid rhododendron


This includes hybrids and varietal forms, which are cultivated by gardeners. The hybrid rhododendron is a garden rhododendron.