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Azaleas: Planting and Design: Home

Azalea Way at NYBG

Azaleas are wonderful additions to the garden. They are easy to grow, look sensational when in flower, and have attractive foliage. Evergreen azaleas provide year-round interest while deciduous azaleas often have exquisite fall color and exhibit an elegant woody framework in winter.

In their native habitats, azaleas are often found growing in or on the edge of woodlands in acidic soil, rich in organic matter, with good drainage. They have a shallow fibrous root system which needs to be considered when caring for them, as explained below.

Azaleas do well in full sun or part shade (about four hours of sun per day). If planted in full sun, they will be more compact and floriferous. If planted in part shade, they will stretch towards the sunlight and form a more graceful habit; flowers will not be plentiful but will last longer.

When used in foundation planting, locate azaleas 3 to 4 feet from the building so that rainfall isn't obstructed by the roof and so that air can circulate around the plants. Avoid planting near highly reflective walls unless on the north side of the building or in the shade. Windy sites are problematic for this shallow-rooted plant in winter; winds and sun can desiccate the foliage of evergreen azaleas in particular. Deciduous azaleas are more forgiving.

Azaleas need good soil structure and plenty of organic matter so that their roots do not dry out. On the other hand, they can suffocate from excess water and poor drainage. Soil compaction around foundations and in yards is a frequent problem. When amending the soil, it is better to prepare the entire bed rather than just the planting hole to create a uniform condition encouraging the fibrous roots to spread. As a general rule, the soil should contain 5 to 10% organic matter.

View of Azalea Way at NYBG; photo by Jason Fernandes
View of Azalea Way at NYBG; photo by Jason Fernandes

Azaleas and other Ericaceous plants prefer a soil ph of 4.5 to 6 (5.7 to 6 is optimal). Test the soil in the planting bed; if it is too alkaline (above 6), use pelletized sulfur to increase the acidity; coated sulfur releases over time so the change is gradual. Read the package instructions to determine the quantity of sulfur needed; apply half the amount in September and the other half in April. Test the soil again the following fall to see if the process needs to be repeated.

Azaleas are not heavy feeders. It will probably be sufficient to fertilize them on a two to three year cycle. Common lore used to recommend fertilizing in the spring, when the plant was pushing growth. University research has since changed this precept; the recommendation now is either to feed in the fall or three times during the growing season for a gradual, consistent effect.

For a fall feeding, fertilize once during late September to the end of October (or when the sugar maples start to turn color). At this point in the season the plant starts to shut down for winter. Instead of encouraging growth, the fertilizer will be taken up and stored as carbohydrates ready to give the plant energy in the spring.

If a continual feed is preferred, divide the overall quantity into three and fertilize your azalea once before flowering, again after flowering and finally in the fall. Organic fertilizer such as Holly-tone 4-3-4 and Plant Health Care 3-4-4 for Azaleas and Rhododendrons are two good candidates.

At the Garden, biostimulants such as M-Roots (humus extracts and mycorrhizal fungi) are ofter added at planting time and then fertilizer is started the following year.

For an established plant, scatter the fertilizer around its drip line (the area beneath the outermost branches) so that the root system reaches outward to get the fertilizer. As a shallow-rooted plant, an azalea will not respond well with fertilizer dug in around its base so gently scratch it in.

Azalea beds need to be mulched to keep the soil moist and cool. Mulch helps minimize the need for watering and helps keep the plant from drying out. Shredded leaves, fine-bark mixes, soil conditioners, Sweet Peat or pine needles are good choices.

It is generally recommended to apply two inches of mulch, but the finer the texture of the mulch material, the thinner the layer that need to be applied. If the mulch is applied too thickly, like a solid mat, water will have difficulty seeping into the soil and it's possible that the azaleas will start to root in the mulch. Do not mulch up to the base of the plant. The mulch should taper off as it approaches the base and not be in direct contact with the stems, which otherwise creates a dark, moist environment ideal for pests, disease and rot.

Mulch will also help prevent weeds that can compete with the azaleas for moisture and nutrients. When weeding around azaleas, it is better to pick weed by hand rather than with a tool so as not to damage the shallow root system.

It is important to keep an eye on your watering practices to maintain a healthy plant. Good cultural practices such as mulching and properly siting the azaleas help to maintain the health of the plants as does knowing when to water.

Water the azaleas immediately after they've been planted. Pay attention to watering needs after the plants have flowered, when leaves and new flower buds are forming, and, of course, during the heat of the summer. Water well in fall too, otherwise the plant will be prone to dehydration in winter.

Plant should get approximately an inch of water (either rainfall or hand watering) per week or a half a gallon per square foot. The standard recommendation is to give small shrubs (less than 3 feet) 4 to 5 gallons of water per week and larger shrubs 7 to 10 gallons per week. When all  is said and done, the golden rule is to water it when it needs it.

If you water too quickly, the water will run off rather than penetrate into the root system. Water percolates into the soil at different rates; slower with clay soils, faster with loam and sand. A simple way to calculate watering time when using a hose is to turn the hose to a very slow rate and clock how long it takes to fill a one-gallon watering can. Multiply that times by the number of gallons needed by the plant to get the length of watering time.    

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