Rhododendrons and azaleas are extremely popular, despite their reputation as being tricky customers! However, by avoiding these basic mistakes, you’ll have beautiful shrubs with spectacular flowers, whether they are for a Japanese-style border or as the year-round evergreen backbone of your garden.
This is the number one cause of failure. Rhododendrons and azaleas need acid soil to thrive (between pH 5.0 and 6.0). If you don’t know the pH of your soil, you can buy simple home test kits for a few pounds. If your soil is alkaline, choose compact varieties and grow them in containers in ericaceous compost – reducing soil pH is difficult. The soil needs to be well-drained but rich in acidic organic matter – dig in composted tree bark, leafmould, decomposing conifer needles, or composted bracken.
Avoid planting when the rhododendron/azalea could get waterlogged in winter or dry out in summer – October or March/April are ideal times. Don’t plant too deeply, as members of the family are surface-rooting and the roots should be just covered. Apply an 8cm-deep loose mulch of chipped conifer bark or other acidic organic matter. Renew the mulch each spring.
Growing in Pots
The only way to grow successfully if you have alkaline soil. Use the biggest pot possible and John Innes ericaceous loam-based compost. Plants will need to be carefully watered and fed. If you’re using soil-less or peat-free potting compost, they can lose their structure, leading to poor drainage, causing leaves to brown and die back. Repot every other year into fresh compost in early spring and replace the top 5cm of compost in between.
Size and Leaf Type
Not doing your homework about your chosen plant’s eventual size can be disastrous. There are tens of thousands of rhododendron and azalea varieties, ranging from dwarf alpines to massive trees.
Two popular RHS Award of Garden Merit winners demonstrate the difference – R. macabeanum is an evergreen tree with cream/deep yellow flowers, 30cm long leaves and an eventual height of 15m and spread of 6m. Meanwhile, R. ‘Ptarmigan’ is a spreading dwarf shrub with dark green leaves and white flowers, height and spread 1m. Read those labels!
All rhododendrons are evergreen but there are two distinct types of azaleas. Evergreen azaleas (Japanese azaleas) typically grow to 40-80cm. Deciduous azaleas reach 120-150cm and lose their leaves in the autumn, often with stunning colours.
Choose a sheltered site with dappled shade but avoid deep shade beneath trees. Dwarf alpine species will cope with full sun as long as the soil does not dry out. Avoid frost pockets and sites exposed to early morning sun, which will damage flower buds.
Even though rhododendrons grow best in areas of high rainfall, soils need to be well drained. They like moist soil, not sopping wet mud. This airless mass will lead to root rot and will kill your plant. To avoid overwatering, use your hands – stick a finger in the soil. If it’s moist, leave well alone and check again in a couple of days. Don’t kill with kindness.
Tap water, especially in hard water districts, reduces acidity around rhododendrons’ roots.
Use rainwater for watering rhododendrons and azaleas, but if your water butts run dry, tap water is better than nothing for a month or so in summer.
Using the wrong fertiliser can lower the soil’s acidity; don’t use lime or other alkaline-based additives. Keep the soil’s pH level to about 5.5. Try to use organic fertilisers, as rhododendrons are susceptible to chemical burn. Fish or seaweed fertiliser is ideal.
Rhododendrons’ root systems are shallow and wide, so don’t use a hoe near the plant. Also, the roots of perennial weeds can get tangled up with your plant. Weed by hand and with care, as you could rip up some of your plant’s roots along with the weed, stunting its growth.
Mandy Watson is a freelance journalist who runs www.mandycanudigit.com.
A plantaholic with roots firmly planted in working-class NE England, she aims to make gardening more accessible to the often excluded – the less able, the hard-up or beginners.
Advocate of gardening for better mental health.