‘Keep The Soil Moist’ – Gardeners Share Important Azalea Growing Advice
Reviewed By COLIN SKELLY
Colin is a Horticulturist and Horticultural Consultant with experience in a range of practical and managerial roles across heritage, commercial and public horticulture. He holds the Royal Horticultural Society’s Master of Horticulture award and has a particular interest in horticultural ecology and naturalistic planting for habitat and climate resilience.
IN THIS GUIDE
Among the most prized and celebrated of flowers, many would say that an Azalea in full bloom represents the Floral Ideal.
Azalea is a much-loved plant in the Deep South, many other American states, Japan, China, and the Koreas.
In fact, the Azalea is an important and integral part of both the landscape and the culture in each of these very different regions.
It is a shrub, deciduous or evergreen, that bears among the most diverse, attractive, and showiest flowers of all.
Overview
| Botanical Name | Rhododendron |
| Common Name(s) | Azalea |
| Plant Type | Shrubs (some are Houseplants) |
| Native Area | Asia, North America |
| Hardiness Rating | Varies by type |
| Foliage | Evergreen |
| Flowers | Bright blooms in Spring |
| When To Sow | March, April, May, September |
| Flowering Months | March, April |
| When To Prune | June |
Sunlight
Preferred
Full Sun or Partial Shade
Exposure
Sheltered
Size
Height
0.5 – 4M
Spread
0.5 – 4M
Bloom Time
May – June
Soil
Preferred
Loam, sand
Moisture
Moist but well drained
pH
Acidic
Azaleas have been hybridised and cultivated for centuries in China and Japan, and the species are not of as much importance to gardeners as the pre-eminent groupings, series, and cultivars.
Although Azalea flowers are considered decorative and ornamental, these gorgeous things are themselves decorated and embellished.
To begin with, no matter what hue the colour may be, it is almost always marvellous, from the palest flush of pink to the most saturated vermilion-red hue.
The form and shape of the flowers is second to none with gently-curved but somewhat different tube-funnel shapes.
As for those decorations and embellishments, we see curled petals, frilled petals, and ruffled petals; hose-in-hose and true double form; deep-hued flecks, contrasting streaks, and all manner of gradating, blotching, flaring, and sectoring.
Hardiness
Azaleas are very wide-ranging genera of plants with different characteristics.
As hybridisation and cultivation have proceeded, newer and newer Azalea varieties combine traits from different parental or genetic lines.
In sunny regions, a majority of Azalea species set up shop under and alongside larger trees where they can enjoy sun in the morning and avoid it in the afternoon.
These plants also like filtered sun and dappled sunlight through tall trees.
Azaleas grow in quite a range of habitats: some species grow in cool, dry regions on mountainsides in China and Japan.
Large swaths of Japan’s Mount Katsuragi and Mount Tokusenjo, to name just two, get covered with Azaleas every spring.1Japan National Tourism Organization. (n.d.). Mt. Katsuragi Azalea. Travel Japan. Retrieved March 10, 2023, from https://www.japan.travel/en/spot/43/
Other species grow in warm and moist regions – for example, Swamp Azalea and ‘Mountain Azalea’ grow in and along the swamps and waterways of Lousiana, Florida, and other South-Eastern States.
Given this variance, the USDA Hardiness Zones of the various Azalea varieties range from down to 3 up to 11 (RHS Zones H1C to H7).
How To Grow Azaleas
As an exceptionally diverse set of plants, Azaleas can be used for nearly every single home, garden, and landscaping purpose from an accent in a rock garden and a single plant in a decorative container to wide boundary hedges and large landscaping bushes.
An azalea that bears a good-sized multi-hued flower can be a superlative single specimen plant; other Azaleas can be just as terrific for mass plantings.
A particular Azalea may be selected (or rejected) for a specific purpose as suggested by the characteristics of that variety.
Besides the hardiness zone, factors that you need to take into consideration include:
- Rate of growth
- Ultimate size of the plant
- Habit
- Evergreen/deciduous
- Size of the flowers
- Fragrance/scent
- Colour and patterning of the flower
Azaleas are shallow-rooting plants with evergreen varieties particularly so, and planting any Azalea even a little too deep in the soil can actually cause the plant to die.
Indeed, plant an Azalea so that the top of the root ball is 2-3cm above the surface of the soil.
Azalea Plant Care
Soil Requirements
In general, all Azaleas need well-drained soils.
A sand- and humus-based loam with little clay or silt would work very well for all Azaleas – these plants will not flourish in heavy clay soils.
All Azaleas thrive in acidic soils, ranging with a pH Slightly Acidic to Moderately Acidic.
Watering
In sunny or warm regions in the summer, the soil should not be allowed to dry out; it should be kept moist.
Mature Azaleas of most cultivars are fairly drought-tolerant but if they go for a significant period without water, they will not bloom profusely or may not flower at all.
Prolonged drought will cause them to shed their leaves and wilt.
Though you may read that Azaleas are ‘drought-tolerant’ be aware that they are not properly or strictly drought-tolerant plants; after all, they are shallow-rooted.
Azalea varieties that are just barely cold-hardy to your region should be mulched up to soil level before the onset of winter.
Sunlight
Though Azaleas are considered ‘shade-loving plants,’ in cool and cloudy regions, like much of the United Kingdom, Azaleas can be grown in full sun.
In warmer, sunnier regions Azaleas are best placed in locations where they get shade from the strong afternoon sun.
However, they must get sun in at least the morning or late afternoon.
In the United Kingdom, full sun is preferable for Kurume and Mollis Azaleas.
In most geographic regions dappled sunlight filtering through tall trees is a very good option for most Azaleas.
In any region, white and light-coloured Azaleas should be protected from full sun or the afternoon sun.
Pruning
You may deadhead Azaleas for three reasons: encouraging new blooms, for aesthetics, and if you wish to avoid self-seeding.
Of course, if you would like to see new and unexpected Azalea varieties sprouting up in your garden, allow some withered blooms to go to seed.
In general, all Azaleas – all groupings – need no more than light pruning and trimming.
For the most part they have ‘neat’ habits and form well-branched plants or bushes.
Severe pruning – unless necessitated by some unavoidable reason such as pest infestation – will probably negatively affect the aesthetics and growth habit of the plant.
By all means trim overgrown areas, or straggly or stray branching, doing so judiciously to the extent of one-third to one-half of the length of the branch.
Some deciduous varieties do require such pruning albeit infrequently.
“Whilst Azaleas generally require little pruning, if your Azalea is old and becomes straggly, you can opt to regenerate it using renovation pruning,” shares Colin Skelly, Master Horticulturist.
“The most cautious option, which I would use in most situations, would be to remove one third of the branches to around 30cm of the ground in winter.
“You should see some new growth emerge during the spring and summer.
“This is a green light to remove a further third of the branches each of the next two years, completing the regeneration.
“If new shoots do not emerge in year one, cease further pruning and focus on mulching and irrigating to promote new growth.”
Azaleas start to develop buds in about two months from the end of flowering season for the following season’s flowers so pruning Azaleas at or after this time would cause a reduction in the flowers you see the following year.
If you have grown an Azalea hedge or bush, you may wish to trim it as you would any other hedge or bush using hedge trimmers but Azaleas are not amenable to such trimming or shaping.
If this is attempted, flowering will be negatively impacted and the least-desired outcome will be affected as subsequent plant growth will be unpredictable and unaesthetic.
An Azalea hedge will need to be pruned and trimmed as would a plant, that is, by picking and choosing branches, and then either very selectively pruning them or cutting them back by no more than half their respective lengths.
