Rhododendrons are usually grown for their spectacular springtime blooms. There are many varies available, from large shrubs suitable for a woodland garden to dwarf alpine types appropriate for a smaller space.

These plants need acid soil, so if you do not have the right soil you should grow your rhododendron in a container. There are plenty of compact varieties suitable for growing in pots. There are also evergreen and deciduous varieties. The evergreens provide good winter structure to the garden, while the deciduous varieties offer the bonus of autumn colour.

In this article, you will find information on how to choose the perfect rhododendron for your garden and how to care for your plant. The article also includes information on how to propagate your plant and what to do if it is beset by any pests or diseases.

Read on to find out how to get the best from this showy springtime beauty.

Plant Overview

Common Name Rhododendron
Scientific Name Rhododendron
Plant Family Ericaceae
Origin Southeast Asia
Height Dwarf varieties can be as little as 40 cm while larger varieties can be 3 metres (ten feet) or more.
Light Most varieties prefer dappled shade. Some species, such as dwarf alpines can tolerate full sun as long as the soil does not become dry
Temperature These plants can cope with most temperatures, however late sub-zero temperatures can damage buds. If a late frost is forecast, you can protect your plant with fleece
Hardiness Mostly full hardy
Soil These shrubs require fertile, well-drained soil that is alkaline. A pH of between 4.5 and 6.0 is required for them to grow well
Fertiliser Use a suitable ericaceous fertiliser in spring
Propagation Propagate by layering or cuttings
Pests Spider mites, rhododendron leaf hopper
Difficulty Medium

Rhododendron Varieties

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Choosing your rhododendron depends largely on what you want from the plant and the space and soil you have in your garden. If you need something for a rock garden or the front of a border and you have acid soil, then choose a dwarf or semi-dwarf variety. If you have a small space or do not have acid soil, then you should choose a variety that will suit being grown in a container. Only choose a large variety if you have plenty of space in your garden and acid soil.

Dwarf varieties

Curlew has lovely lemon flowers in April and is a tiny variety that reaches only 40 cm (16 inches).

Chipmunk has bright pink flowers in June. It is a slow growing plant that reaches 40 cm (16 inches) in height.

Carmen has lovely deep red bell-shaped flowers against small dark leaves. It reaches a height of 40 cm (16 inches) and blooms in April.

Semi-dwarf varieties

Lucy Lou has white flowers with black stamens in March. It reaches a maximum height of 90 cm (3 feet).

Calostrotum Gigha is a lovely pink variety that reaches 90 cm (3 feet) and flowers in early May.

Crane has abundant creamy white flowers in April and is an easy to please and easy to grow little shrub. Its maximum height is 90 cm (3 feet).

Larger varieties

Brambling has bright pink clusters of flowers and lovely dark foliage. It reaches a height of 1.5 metres (5 feet) and flowers in April.

Barnaby sunset has pale yellow flowers that are pink on the outside. It reaches a final height of 1.80 metres (6 feet) and flowers in early May.

Strawberry cream has a lovely mixture of pink and cream flowers. It reaches a maximum of 1.5 metres (5 feet) in height and flowers in early May.

Baileyi has striking purple flowers that are smaller than other varieties. It flowers in April and reaches a height 1.5 metres (5 feet).

Alena has white flowers that are lightly scented. It flowers in early May. This plant has tough vigorous growth and is very hardy. It reaches 1.80 metres (6 feet) in height.

Captain Jack has bold, red flowers and large, pale leaves. It grows to a maximum of 3 metres (10 feet) tall and flowers in June. This variety will need to be planted in light shade.

Rhododendron Care

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If you are aiming for a woodland garden and have plenty of space the choose one of the larger varieties. However, if you have a smaller site, consider a dwarf alpine variety which will be happy in a sunny border or rock garden. Compact varieties do well in large pots on patios.

You should plant your rhododendron in fertile but well-drained soil with a pH value of between 4.5 and 6.0. If you do not have this kind of soil, then choose a compact variety and plant it in a pot.

It is important to choose the position for your plant carefully. Most varieties need a sheltered spot away from cold dry winds and out of frost pockets. They will enjoy a situation in dappled sun and do not like really deep shade. You should also avoid a position where there is strong morning sunlight, too.

Light requirements

Most varieties of this shrub prefer dappled shade. They do not like to be under a dense canopy of trees where the shade will be too deep. Some varieties, such as dwarf alpines will grow more happily in sun, as long as they are kept from drying out. These shrubs prefer a sheltered situation and do not like exposed and windy sites.

Water requirements

These plants do not like to dry out so regular watering in dry spells is essential. However, avoid watering too frequently as this increases the risk of fungal diseases and root problems. A thorough dousing once a week in dry weather is usually about right. If the leaves of your plant begin to curl this is a sign that it is in desperate need of water. Try not to let it get to that stage as wilting places a lot of stress on the plant.

Tap water in some areas of the country is quite alkaline so use rain water wherever possible.

Soil requirements

Your shrub will require acid soil and if planted in a container you should use ericaceous compost.

Fertilizer requirements

Fertilise in spring with a product specifically designed for ericaceous plants. A mulch of pine leaves can also benefit this shrub.

Planting

You should plant your rhododendron in spring after all danger of frost has passed.

Prepare the soil by digging in some organic matter if required. Dig a hole that is twice the width of the rootball but not too deep. Soak the rootball of the plant thoroughly before planting. Rhododendrons should be planted quite high in the ground, to ensure that it is at the same height as it was in the pot. The roots should only just be covered with soil.

Once planted, water well and then cover the area surrounding the plant with a mulch of conifer bark.

If you are planting your shrub in a pot, choose an ericaceous loam-based potting compost. You will need a pot a few inches larger than the rootball and it should have plenty of drainage holes. Cover the holes with some crock to prevent them from becoming blocked.

Maintenance

Once you have got the essentials of a good position, the right soil, and a regular watering regimen, rhododendrons are quite self-sufficient.

Repotting

You should repot your plant every other year. Choose a pot slightly larger than the current one. Alternatively, you can keep your plant in the same pot if you cut back one third of the roots to allow room for fresh compost. In the intervening year, scrape off a couple of inches of the compost and replace with fresh.

Pruning advice

Rhododendrons do not generally require pruning. You should simply remove any dead wood. However, if you need to prune your shrub to restrict its size you should do this immediately after flowering to ensure you do not interfere with the production of the following year’s buds. Cut back any long, straggly growth to keep a compact and bushy shape to your plant.

After pruning you should feed and water your shrub well to encourage new growth.

Rhododendron Propagation

Rhododendron can be propagated by semi-hardwood cuttings or layering

Layering

Layering is possibly the simplest way of propagating this plant but be prepared for it to take quite some time. It may take up to two years before your plant is ready to be potted up.

Choose a healthy non-flowering shoot that can reach the soil surface without breaking. At the section that is in contact with the soil, remove the leaves and make a cut at the underside of the stem. Do not cut more than halfway through the stem. Apply hormone rooting powder to the cut.

Dig a hole about 5cm (2 inches) deep and peg the stem down with a sturdy forked twig or bent wire. Water well.

Cover with compost and firm in. Place a cane into the ground near the end of the stem and tie the stem to the cane to keep it off the ground. Keep the stem well-watered.

Semi-hardwood cuttings

You should take cuttings of your plant in late summer or early autumn. Cuttings are taken from the current season’s growth. The stems you choose should be slightly woody at the base but not old and brittle.

Cuttings should be taken early in the day when the stems are full of water.

Prepare a 4-inch pot by filling it with potting compost, filled an inch from the top. Make several holes around the edges with a pencil.

You may get more than one cutting from each stem but do not use the woody part at the base or the very soft tip. Divide your stem into cuttings of around 10 cm making the base cut just above a leaf node. Remove the lower leaves and dip the base in rooting hormone powder. Insert your cuttings into the prepared holes and firm in. Mist the soil.

Cover your pots with a large plastic bag secured with an elastic band. Place them somewhere that is warm and sheltered but out of direct sunlight. Alternatively, they can be kept in a greenhouse or cold frame.

Check the cuttings weekly and give them an airing and some water. Remove any dead or dying material. Once the cutting starts to put on new growth you can remove the plastic bag. Continue watering regularly.

Common Rhododendron Problems

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Rhododendrons are usually healthy and trouble free if they are planted in suitable conditions. Occasionally they may succumb to one of the following pests and diseases.

Pests

Spider mites

If the leaves of your plant become yellow or brown, check for spider mites. These tiny bugs can suck the sap from your plant. They are hard to see, as they are so small. However, if you place a piece of white paper beneath the plant and give the plant a shake some will drop onto the paper. They can be as small as grains of pepper. These bugs will probably not give your plant too much trouble if it is generally healthy. You can spray off the mites with a jet of water if they are a problem. Encouraging predators such as ladybirds can also help keep them under control.

Rhododendron leafhopper

This is a creamy white wingless insect that lives on the underside of the leaves. The bugs do little damage to the plants foliage; however, the females lay eggs in the buds and this is thought to lead to allow a fungal disease to infect the buds. This disease is known as bud blast and is discussed in the diseases section that follows. There are insecticides that will help to control this bug. They will need to be applied repeatedly to break the life cycle and shouldn’t be used when the plant is in flower as they can harm pollinating insects.

Diseases

Bud blast

If your plant becomes infected with bud blast the flower buds will go brown and die but remain attached to the plant. The buds may also go grey and become covered in tiny back bristles. You should remove all affected buds immediately if practical. As with all fungus infections, reducing humidity can help. Water at the base of the plant rather than on the leaves, remove weeds from the area and cut back any plants that are encroaching on your shrub’s space. You may also want to thin out your rhododendron to allow air to circulate.

If your plant is severely affected, you may need to remove and destroy it and plant a more resistant variety in its place.

Powdery mildew

Powdery mildew shows as a white powdery coating on the leaves and stems of your plant. On rhododendrons, it is usually on the underside of the leaves and can be hard to detect but you may see pale patches on the surface of the leaves.

Do whatever you can to reduce humidity in and around the plants if it is affected.

Leaf spot

Leaf spot shows as small spots of yellow, brown or black on the leaves. These may spread until they create larger patches. It is not usually wise, or practical to remove the leaves. Checking that your plant is in suitable conditions will help because diseases often occur when a plant is not in its ideal situation. Watering at the base of the plant and increasing air circulation around the plant should help. There are fungicides available if the problem is severe.

FAQs

Q The leaves of my rhododendron have turned yellow. What is wrong?

A

The older leaves of a rhododendron will turn yellow and then drop off when they reach the end of their life. However, if you plant is losing lots of leaves there are two possible causes. The first is that the plant is sitting in wet soil.

These plants require good drainage. If you can improve the drainage around your plant by the addition or horticultural grit this might help. If your plant is in a container, ensure that there are plenty of drainage holes and water it well, but without keeping it soggy.

The other possibility is that your shrub is planted too deep. You should be able to feel the rootball in the soil, if not you should replant it at a higher level.

Q Why does my rhododendron not flower?

A

If your plant formed buds but they turned brown this is sometimes caused by frost damage. Bud blast can also cause buds to die. If the plant is not producing buds at all then it may be that its position is too shady. In addition, the application of a fertiliser after June can encourage leafy growth at the expense of flowers.

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