how to plant, grow & care for rhododendrons
Blowsy pinks, saturated purples and the purest, brightest reds, rhododendrons come in a whole range of dramatic colours, bringing a real bit of razzmatazz to the spring and early summer garden. For larger spaces, choose rhododendrons, which tend to be evergreen. Azaleas, their near relatives, tend to be smaller and can be evergreen or deciduous. Both offer varieties with beautiful fragrance, and both will attract hordes of bumble bees, hungry for the pollen and nectar. Take a look at our range of low maintenance, trouble-free rhododendrons, ready to plant out or pot up in your garden.
details
- Common name: Rhododendron/Azalea
- Latin name: Rhododendron
- Type: Shrub
- Height: 60x60cm for indoor varieties up to 2.5x2.5m for outdoor varieties
- TLC rating: Easy
- Aspect: Part shade
- Planting position: Woodland gardens; borders (back or middle, depending on size);container gardens
- Suitable for pots: Yes (particularly azaleas)
- Good for pollinators: Yes
- Good for cut flowers: Yes
calendar
seasonal checklist
spring
- Plant out rhododendrons in the garden.
- Apply a thick layer of acidic mulch (eg leaf mould or conifer bark chippings) around plants while soil is still moist.
- Feed potted plants in March when signs of new growth start to show.
summer
- Water well with rainwater where possible.
- Feed potted plants again after flowering.
autumn
- October is also good for planting, so roots can establish before winter.
winter
- Plan which rhododendrons you’d like to grow next year.
how to plant & grow rhododendrons
where to grow rhododendrons
Soil type: Rhododendrons need rich, acidic (pH5-6) and moist but well-drained soil to thrive. If you have alkaline soil, you can grow rhododendrons in pots using ericaceous peat-free compost.
Aspect & position: Dappled shade is perfect for most rhododendrons, though many will grow in more sun. Generally, the larger the leaf, the more shade they require. Avoid planting close to large trees or at the base of walls or fences which could deprive them of moisture.
when to plant rhododendrons
Rhododendrons can be planted at any time of year but the best times are March/April or September/October. If planting in the summer months, remember to water well.
planting our 4L+ rhododendron plants
IN THE GROUND
Choose a day when there is no frost on the ground and avoid planting if your soil is very waterlogged.
1. Prepare the planting area by forking over the soil and incorporating plenty of organic matter (well-rotted manure, home-made compost or multi-purpose peat-free compost). Pick out any large stones and visible weeds as you go.
2. Water your plants well before planting. You can also soak them for 20 minutes in a bucket or wheelbarrow of water if they seem particularly dry.
3. Dig a hole twice the size of the root ball, incorporating plenty of acidic organic matter such as pine needles, leafmould or composted tree bark.
4. Place the plant in the hole so the roots are just below the surface of the soil and back fill with soil and your organic matter, and firm in gently. You should be able to tug gently on the leaves without the planting lifting out of the ground.
5. Water well and mulch with a thick layer of bark chippings.
6. Do not plant too closely – leave a distance of the plant’s maximum height between plants.
IN A CONTAINER
1. Choose a pot large enough to give the roots space to grow and spread.
2. Make sure it has drainage holes, and place some crocks (broken pots and pottery) or a layer of horticultural grit at the base.
3. Fill your container with ericaceous peat-free potting compost with some fertiliser mixed in, leaving a space for the plant.
4. Position the plant so it sits at the same level as it was in the original pot, and firm in well.
5. Water well and add more compost if the surface has sunk more than an inch below the rim of the pot. Place in dappled shade and check the soil every few days, watering well if it feels dry.
6. Repot every two to three years.
how to care for rhododendrons
watering
Rhododendrons need water so water well, using rainwater where possible, ensuring they don’t become waterlogged. Mulch annually with a thick layer of acidic organic matter.
fertilising
Rhododendrons in containers are likely to need additional nutrients. Feed with a liquid feed every couple of weeks through the growing season, or add a slow release granular fertiliser to the pot in spring.
deadheading
Remove spent flowers to keep your shrub looking tidy.
pruning and trimming
Rhododendrons need little in the way of pruning, but if your plant needs shaping, cut back shoots lightly immediately after flowering. You should also remove any dead, diseased and dying branches at the same time.
propagating
Rhododendrons and azaleas are easy, if slow to grow, using a technique called layering.
- In spring (best for evergreens) or autumn, choose a lower branch that can be bent down to touch the soil.
- Clear the ground beneath it, removing any weeds and incorporating plenty of ericaceous peat-free potting compost to form a small mound.
- Choose a section of the stem which will be in contact with the soil and which includes a leaf bud, and wound it by cutting off a thin section of bark until you can see the white wood beneath. This is where new roots will form.
- Pin the branch, including the wounded area, down onto the soil and loosely tie the tip to a cane to encourage vertical growth.
- Water if dry.
- Roots should set in between one and three years, depending on the variety, at which point the branch can be severed and the new plant transplanted to a pot or its final growing position.
pests, diseases & common issues
deer
Deer eat rhododendrons and azaleas, so protect your plants with fencing if they are a problem in your area.
why is my rhododendron dying?
The most common causes are poor drainage leading to waterlogging and root rot, under watering or severe cold. Other reasons may be that the soil is not acidic enough, or that the plant has been over-fertilised.
why is my rhododendron not flowering?
Lack of water is a common cause, as is lack of nutrients, particularly potassium which helps with flower formation. Your plant may also have been pruned at the wrong time of year, removing flower buds. If pruning is necessary, do it just after flowering in early/mid-summer so buds have time to form for the following year.
why are my rhododendron leaves turning yellow?
This is most likely because the plant lacks iron because your soil lacks the necessary acidity. Changing soil acidity is not easy to do, so if this is the case, try growing your plants in pots using ericaceous peat-free compost.
why are my rhododendron leaves curling?
Curling leaves are usually a sign that the plant is trying to retain moisture, so it could be that your soil is too dry, or that cold winter winds are desiccating the leaves. In both cases, water well and apply a thick layer of acidic mulch around the plant’s crown. Be careful not to overwater though, as this can also lead to leaf curl.
rhododendron vine weevil
Vine weevil can damage rhododendrons, especially those grown in pots. Notched leaves are a symptom of the adult beetles feeding, but it is the larvae feeding on the roots that cause most damage. If you spot vine weevil grubs, repot plants removing as many larvae as possible, and encourage more wildlife into your garden – birds, frogs and toads all eat them. If an infestation is severe, apply nematodes into moist soils in August or September.
rhododendron bud blast
Rhododendron bud blast is a disease spread by leaf hoppers which turns buds brown and later black. Remove and destroy the buds as soon as you see symptoms.
rhododendron buds not opening
Your plant may have been damaged by frost, or may need more sun. Move it to a more sheltered space if you can, or protect with horticultural fleece or bracken stems in cold spells.
rhododendron leaves drooping
Rhododendrons need water, so keep your plants well watered in the growing season.
how to get rid of powdery mildew on rhododendrons
Powdery mildew – a fungal disease causing dry, dusty patches on deciduous azaleas and discoloured blotches on rhododendron leaves – can be an issue in dry periods or where plants are closely spaced. It is difficult to treat, but you can try to prevent it by spacing plantings to allow good air circulation; avoiding planting in heavily shaded areas and by choosing resistant varieties. At Perch Hill we use a homemade spray as a preventative. To make it, mix 1 tsp bicarbonate of soda, 1 tsp vegetable oil and 1 tsp soap (we use Uncle Tom’s natural soap) with 400ml water and pour into a spray bottle. Shake well and spray on leaves, including the undersides.
Rake and destroy affected leaves – do not add them to the compost.
rhododendron leaf gall
This is most common on azaleas where the leaves become pale and swollen and covered in white, dusty spores. If you spot this, remove and destroy the affected leaves promptly before the spores can spread.
rhododendron rust and other leaf spots
Spots on rhododendron leaves can be a sign of rust and other fungal diseases. We don’t recommend fungicides, so advise that you rake up and dispose of fallen leaves around the plant and mulch well with bark chippings. To avoid fungal diseases, choose resistant varieties and plant plants with adequate spacing so that air can circulate. It’s also a good idea to avoid overhead watering, and to water in the morning so that moisture does not sit on the leaves.
rhododendron honey fungus
Honey fungus is a serious fungal disease which requires drastic action. If you spot honey coloured toadstools around your plants and white fungal growth underneath the bark, dig up any affected plants removing as much of the roots and any rhizomorphs (black bootlace-like structures which spread the disease) as soon as possible. Dispose of the top 45cm of soil and avoid replanting in the same area for six months.
frequently asked questions
how to pronounce rhododendron?
‘Row-de-den-dron’
can you move a rhododendron?
Yes, you can move established rhododendrons. In autumn or early spring, dig up the plant being careful to retain as much of the rootball as possible. Dig a hole two to three times larger than the rootball and incorporate some peat-free ericaceous compost or acidic organic matter. Position the plant at the same level as it was in its previous location, and back fill. Water, feed and mulch.
can i prune rhododendrons in summer?
Rhododendrons generally don’t need pruning but if you need to cut out dead, damaged or diseased wood, then do so immediately after flowering in early to mid summer.
which rhododendron is invasive?
Rhododendron ponticum is invasive and should not be planted.
are rhododendrons poisonous?
Yes, rhododendrons are poisonous to humans as well as cats, dogs and horses if eaten.
are rhododendrons evergreen?
Rhododendrons are usually evergreen and azaleas (part of the rhododendron family) are usually deciduous. Smaller Japanese azaleas are evergreen and perfect for pots.
what's the difference between azalea and rhododendron?
Azaleas are part of the rhododendron family but have several differences to rhododendrons. They tend to have thinner, hairier leaves than rhododendrons, have flower clusters with fewer blooms, and each of these flowers has fewer stamens – typically five or six, compared with rhododendron flowers which have 10 or more.
do rhododendrons flower twice?
Generally, rhododendrons do not flower twice, but occasionally a few buds may open during warm periods in autumn or winter.
how big do rhododendrons get?
Some rhododendrons can grow into huge thickets several metres high and wide, so always check mature size before planting.
what to grow with rhododendrons?
Rhododendrons look great in woodland-style plantings and combine well with hydrangeas, astilbes, pieris and mahonia.
how to cut & arrange rhododendrons
Though not commonly seen, rhododendrons make great cut flowers – especially if you choose the scented varieties – lasting for up to a week in the vase. Snip the stems cleanly at an angle while the blooms are still fresh, and then split the woody stems by an inch or two so they can take up water more easily. They combine well with the flowers of other shrubs including cornus, lilacs and viburnum.
