Getting the best from azaleas and rhododendrons
Azaleas and rhododendrons are the jewels of the late spring garden. Their exquisite blooms bring notes of exotic colour to pots and containers, beds and borders and lightly shaded areas under trees. Some are compact enough for the smallest gardens, others require the space of a woodland where they can reach massive proportions. All fall into the group known as ericaceous plants. These need acid or neutral soil to thrive and struggle or fail in alkaline conditions. However those gardening on unsuitable soil can grow the more compact varieties in pots and containers using a lime-free ericaceous compost.
Growing conditions
Azaleas and rhododendrons have dense fibrous root systems that rarely spread much beyond the extent of the foliage. They dislike waterlogged soil but do require adequate moisture throughout the growing season. In periods of drought the large-leaved rhododendrons tend to wilt and if this happens watering is necessary.
Although most will grow in open, sunny situations they prefer semi-shade and a cooler growing conditions. The light shade under birch trees or other trees with a light canopy is ideal, as long as the soil is not too dry.
They are particularly useful in small, shaded gardens when grown in pots and containers. A rhododendron or evergreen azalea in a pot will bring year round interest and colourful spring blooms to shady situations where other plants fail to perform.
Once planted and established azaleas and rhododendrons are long-term garden plants that bring many years of pleasure. They need little attention, but some extra care helps to ensure a spectacular spring display every year.
Feeding
Rhododendrons and azaleas are light feeders, in other words they require small quantities of nutrients. They are prone to iron deficiency which causes yellowing of the leaves and poor growth. This is the problem on alkaline soils. The plants cannot take up iron in these conditions and growth suffers.
Most standard fertilisers are unsuitable for them because they release larger quantities of food too quickly, therefore a specialist fertiliser, containing the correct balance of nutrients is required. Vitax Azalea, Rhododendron and Shrub fertiliser is a slow released organic-based fertiliser with added iron and other essential nutrients. Just two applications a season will give the plants exactly what they need for growth and flowering. Sprinkle a small handful of pellets around the plants in early spring and repeat as the flowers fade. If the weather is dry, water thoroughly after application.
Vitax Azalea, Rhododendron and Shrub fertiliser can be used on plants in pots and in the open ground.
Deadheading
Removing the faded flowers from evergreen and deciduous azaleas is unnecessary. The flowers fall away leaving the seed-heads. If these develop they rarely affect the new growth which is produced after flowering.
The large flowered rhododendrons retain their seed-heads when the flowers fall. Removing these by carefully snapping them off just above the leaves helps the new growth shoots to develop quickly after flowering. This is not possible on mature plants, so feeding following flowering really helps to replenish the resources that the plant puts into flower and seed production.
Pruning
Unlike many other shrubs, azaleas and rhododendrons require no regular pruning, only the removal of any damaged or dead wood. Older plants can become leggy, if this happens hard pruning after flowering, followed by feeding and regular watering, will rejuvenate them and encourage new, vigorous growth.
What about other ericaceous plants?
Other ericaceous plants include heathers, pieris and blueberries. Camellias and magnolias are not ericaceous, but prefer acid to neutral soil and will benefit from Vitax Azalea, Rhododendron and Shrub fertiliser.
Andy McIndoe for Vitax
Spring 2018
