How to Grow Rhododendrons & Azaleas

Rhododendrons need an open soil mixture. Very heavy (clay) and very fine particles (silt) are not suitable. To improve soil, making it more open (i.e containing air pockets) organic matter should be added: leafmould is the best. Alternatives are compost (own or bought), composted bark or conifer needles or perlite/grit. There is little point in spending money on rhododendrons and azalea if you are not prepared to do some soil preparation. Improve the soil in an area much bigger than the rootball so there is room to grow. If drainage is good, then soil preparation need no more than 30cm (12in) deep. Peat can be used to improve the soil, but it is not as useful as products listed above. It is acidic and helps hold moisture but it has little structure, no feed and no mulching value. Ericaceous compost contains mostly peat.

In heavy clay soil, a raised bed is best: 30-45cm deep on top of the clay soil. Make a soil-compost-bark-peat etc mix and plant into this. Glendoick Garden Centre Pagoda garden is an e

Rhododendrons must not be planted too deep. The rootball should be just below the surface and no more. If you bury the rootball, you may kill the plant. Do not put thick layers of mulch on top of the rootball.

Ensure plant is well-watered (but allowed to drain) before planting. Mix some organic matter (see above) into the existing soil as a planting medium. Soil should be firmed up around the roots but do not stamp on the rootball. This only compacts the soil and buries the plant. For bare rooted stock, October to early April is the best planting time. Container stock can be planted at any time but if planted May-August must be well watered through the first growing season.

Deadheading is largely a cosmetic exercise: only a few varieties produce seed at the expense of growth.

Anything you like as long as it does not take all the moisture from the roots. So avoid greedy trees, shrubs and ground cover such as roses, Vinca and heathers. In the wild rhododendrons grow with other Ericaceous plants such as Enkianthus, Kalmia (USA), Vaccineum, Gaultheria, Pieris, other shrubs such as Berberis, climbers such as Clematis, and perennials such as Aquilegia, Primulas, Meconopsis, Lilium Rheum, etc. For late summer colour, use Hydrangea, Eucryphia, Sorbus and other berrying plants.

Varieties with large leaves, early growth or which are on the tender side for your climate require shelter from wind, particularly from south westerlies and north easterlies. Options if shelter is poor: 

1. Plant a shelter belt of vigorous trees and shrubs.

2. Use rokolene (spun plastic membrane) or similar material to help plants establish. 

3. Plant hardy wind-tolerant rhododendron varieties on the windward side and less hardy varieties inside these.

Rhododendrons & azaleas do not need much feeding. If they look healthy and flower well, don't bother. If you are in a hurry or plants look yellow or sparse, you can feed with almost any granular fertiliser but beware of high nitrogen mixes as they can burn foliage. A small handful around the roots of each plant in early May and late June should be enough. Don't fertilise later as it encourages soft growth at the expense of flower buds. Liquid feeds are good for containers. We don't use sequestrene: it is only required to rectify iron deficiency usually because the pH is too high (alkaline). We have our own Rhododendron feed available at our garden centre. Growmore is OK but it it can burn so dont put on too much. Bone meal is of limited value. 

Well.. we aren't going to tell you how to do that, are we? 

Dwarf rhododendrons & evergreen azaleas are quite easily rooted in a propagator. With bottom heat, rooting will be quicker. In a cold frame rooting may take up to 6 months or more. Deciduous azaleas, hardy hybrids and species are difficult. Some species need to be grafted. Don't waste time growing seed from gardens: unless it has been control (hand)-pollinated, it will be hybridised and usually worthless.