All About Azaleas
Azalea Grow Guide
There are thousands of varieties, hybrids, and wild species of azaleas and rhododendrons. Gardeners can choose from low growing ground cover azaleas, to treelike rhododendrons over 25 feet tall; from the early flowers that bloom in spring, to repeat bloomers like ‘Autumn Embers‘ that flower through late summer; from deciduous rhododendrons that are hardy to Zone 4, to evergreen azalea flower plants like the popular ‘Formosa’ variety that almost defines Deep South gardens. All are noteworthy for their brightly colored, long lasting flowers and their ease of cultivation.
Use this guide to grow azalea plants and to lead the way to flowers year after year.
What’s the difference between an azalea and a rhododendron?
Actually, the names are interchangeable since all are in the genus Rhododendron. In recent years the common name, “rhododendron”, has come to be used for most of the Rhododendron species that have large, leathery, evergreen leaves and ten stamens per flower; and “azalea” is used for most of the ones with smaller (deciduous or evergreen)leaves, and five stamens. But, there are exceptions. Here we refer to all members of the genus Rhododendron as azaleas.
Azalea bushes are easier to transplant and easier to maintain than most shrubs. Just follow a few simple guidelines…
The best time to plant out azaleas is during the moderate weather of late spring or early autumn. Azaleas can be damaged by strong winds and should be planted where they get some shelter from the wind, such as near a building or a stand of evergreen shrubs or trees. For evergreen azaleas, select a position in the landscape that will provide some shade during the mid-day summer heat. Dappled shade is ideal. Deciduous azaleas usually flower more abundantly in full sun, but still do quite well in partly shady places. The hotter the summers, the more shade azaleas should get, both the evergreen and the deciduous types. However, full shade all day long is to be avoided except in tropical (Zones 10-11) climates.
Azaleas need a soil that is well drained and rich in organics, although sandy soil that is low in organics is also suitable as long as it gets regular top mulching. Rocky or clayey soils are not suitable. If your soil remains soggy for long periods, don’t plant azaleas. To test if the soil is well drained enough, dig a hole six inches deep and six inches across and fill it with water. If the water has not drained from the hole within three hours, the soil is too poorly drained for azaleas.
Azaleas are acid loving plants, prefering a pH between 4.5 and 6.0. If your soil is calcareous, limey, or has a pH higher than 7, you should forget about growing azaleas in the ground. If your soil pH is between 6.0 and 7.0, you can lower it by adding granular sulfur or iron sulfate to the soil. Work the sulfur into the soil about six inches deep. See the accompanying table for amounts to use. If possible, you should get the soil pH corrected at least nine months before planting azaleas.
To lower the pH of a typical loamy soil to 5.5:
6” into the soil
6” into the soil
|7.0||3.5 lbs/100 sq ft||21 lbs/100 sq ft|
|6.5||2.5 lbs/100 sq ft||14 lbs/100 sq ft|
|6.0||1.0 lb/100 sq ft||6 lbs/100 sq ft|
Consider the mature height of the azaleas you will be planting and space them about half that far apart. Dig a hole with a diameter about twice that of the pot the azalea came in, and about the same depth. Thoroughly water the soil in the plant’s pot before starting, then place the pot on its side and slide the root ball out. If the plant is stuck, you can slip a long-bladed knife around the inside edge to loosen it. Gently loosen some of the roots along the sides and bottom of the root mass, and pull them outward so they are not encircling the root mass. It shouldn’t be necessary to prune any of the roots unless they are wound around the circumference of the pot. In that case the offending roots should be shortened so that when they are in the ground they will grow outward and not continue growing in a circle.
Mound up some soil in the middle of the hole and place the center of the azalea’s root mass on top of the mound, spreading roots out all around the center. Backfill until the shrub’s stem is at the same level it was in the original pot, never lower. You may have to pull the plant up as you backfill. Too shallow is better than too deep. When the hole is half filled, give it and the roots a good soaking of water. When the water has drained, readjust the depth of the stem if necessary and finish filling the hole. Gently tamp the soil down with your hands.
Build a 3-6 inch high dike of soil around the outside of the root zone. This will help impound water over the roots while it sinks into the soil. Water thoroughly. Spread organic matter 3-6 inches deep over the root zone and beyond to help keep soil moist. You can use hay, straw, leaves, pine needles, pine bark or wood chips, grass clippings or compost. Do not use mushroom compost as this contains lime and can raise the pH. Do not fertilize or use plant food.
Keep your azaleas well watered during their first growing season. If planted in the fall or winter, you can water once every week or two. Planted during the growing season, they should get watered every day or two for three or four months. If you’re having a dry spell, or your soil is very sandy, you should water every day for the first three or four months. This can also cause yellow leaves. The most common reason for a newly planted azalea to die is lack of enough water.
Once established (after a year of growth), azaleas can tolerate moderate dry spells and should not need any supplemental watering unless it hasn’t rained in three weeks or more.
Azaleas have shallow roots, so they should be well mulched to prevent the soil around those roots from drying out or getting too hot. Use an organic mulch that will decompose and add nutrients to the soil. You shouldn’t have to provide additional fertilizer for azaleas that are well mulched. Try to maintain a mulch layer 2-5 inches deep around the azaleas at all times, but keep it a couple inches away from the trunk itself.
If you remove spent flowers right away, the plants will put their energy into vegetative growth rather than fruit and seed production. Evergreen rhododendrons especially should be deadheaded as soon as flowering is complete, otherwise they will have fewer flowers next year. (This is not usually the case for most deciduous azaleas.) Cut or break off only the spent flower cluster, being careful you don’t remove next year’s buds which are already clustered at the base of the old flower cluster.
Azaleas generally do not need any pruning, but if necessary to maintain shape or size, do it right after flowering. Azaleas start forming their flower buds for the next season very soon after blooming, and you don’t want to reduce next year’s gorgeousdisplay.
To rejuvenate an old spindly plant, cut it back by a third or more. The cut branches will resprout regardless of their proximity to other branches.
Once established, azaleas are very low maintenance shrubs, but you will need to water them during prolonged periods of drought.