Growing Azaleas
By Bob Chapman
All azaleas, deciduous or evergreen, have the same cultural requirements. They prefer light shade with morning sun, acidic soils, continually moist conditions, sufficient air at the root zone, the crown of the plant above the soil line and no cultivation. When these conditions are met, nothing exceeds their beauty, spring to early summer. Azaleas are excellent container plants, growing for many years in a suitable container.
-Acidic Soils
One premier grower of azaleas states that you must plant azaleas in pure peat moss to grow them successfully. Others use a formula such as 50% peat moss, 30% sand and 20% perlite. Some commercially-prepared potting mixes also contain the right materials for growing these plants. Most of these prepared mixes meet the acid soil requirements for azaleas. Some gardeners use raised beds to grow azaleas, thus keeping them away from contamination by predominantly alkaline soils.
-Watering Requirements
Never let the soil dry out when growing azaleas. Leaves may turn brown and fall. Using the recommended mixes allows longer periods between waterings as these soils hold large quantities of water.
-Air at the Root Zone
Heavy or waterlogged soils deprive the roots of azaleas of oxygen. They suffer as a result. Using the recommended mixes allows air and water retention.
-Crown above the Soil Line
Place the top of the root ball of your azalea 1/2 to 1 inch above the soil when planting. This prevents one of the major killers of azaleas, crown rot, a fungal disease.
-Mulch Azaleas
Azalea roots are near the surface and are easily injured if cultivated. Place thick mulch around and under your azaleas. This will aid in weed control and help retain moisture.
-Fertilizing Azaleas
Feed your azaleas when the new growth starts in the spring, at bloom time, then monthly until August. Use an acid fertilizer, one prepared for rhododendrons, azaleas and camellias. An acid food will help keep the planting mix acidic, while providing all the nutrients an azalea needs for healthy growth.
-Pruning Azaleas
Evergreen azaleas branch wherever a leaf has joined the stem. New growth will emerge from these leaf nodes, even if the leaf is long gone. Pinching the shoots of evergreen azaleas during the growing season, and after blooming, makes the azalea compact and will provide more blossoms next spring. These azaleas bloom on the new growth produced in the previous summer. Pinching (cutting off) shoots are best done in the middle of the summer, but can be done as late as August. Deciduous azaleas are pruned when dormant. Cutting off errant stems or shaping the plant is done in the winter. Older, woody stems, those no longer producing flowers, are removed, allowing new, young shoots to develop. These younger shoots are the ones that flower profusely.
COMMON PROBLEMS WHEN GROWING AZALEAS
-Iron deficiencies
When the older leaves are pale, with the veins showing green, it indicates a shortage of available iron. Use iron sulfate or a liquid iron sprayed on the leaves. You can also use Miracle-Gro, a liquid fertilizer containing iron, and spray it on the leaves, to feed the plant and correct iron deficiencies.
-"Salt Burn" of the Leaves
Toxic salts in soils are carried to the tips and edges of the leaves. Concentrations of these salts kill the leaf cells, turning them brown. If growing a lot of salt sensitive plants, consider purchasing a moisture-pH and light meter for about $10. Or purchase a soil testing kit, one for pH, and test the soil. There are single-test kits, such as Rapitest or the Sudbury Garden Soil Tester which gives ten tests, and both are quick, easy and reliable. Try to maintain a pH between 5.5-6.5 for good growing of azaleas. If the pH is high, above 7.0, flush the soil, then spread 1/4 to 1/2 cup of aluminum sulfate around and under the azalea and water it in. This will lower the pH quickly. Wait two weeks and test again. If the pH is still too high, reapply the aluminum sulfate. The regular use of an acidic fertilizer helps control the soil pH. After flushing, or leaching the soil, feed azaleas with a mild application of a water-soluble complete fertilizer (such as Miracle-Gro) to replace any nutrients washed out of the soil.
-Insects
There are chewing and sucking insects that occasionally bother azaleas. The chewing insects that put holes in leaves or eat the edges of them are controlled with malathion, sevin or Orthenex. Sucking insects, such as aphids, spider mites, scale and whitefly can be controlled with a product containing pyrethrins or the use of Orthenex. Organic gardeners use horticultural oil, pyrethrins, ryania, sabadilla and rotenone to control insects, in addition to hand picking or hosing off invading insects.
-Root and Crown Rots
These diseases, mostly fungi, thrive in saturated conditions. Keep the soil moist, but not saturated. If these diseases strike they usually will kill the plant. When planting new azaleas, place the crown (the part that emerges from the soil) above the soil line to prevent crown rots from attacking the stems. Azaleas, having their roots at the surface, are easily transplanted at any time of the year.
Summary
Azaleas will grow and flower for many years if proper conditions are provided. Plant them in loose, acidic soils, maintain the acidity by applying aluminum sulfate as needed, watering them often enough to never let the soil dry out, and feeding them during the growing season. Following these guidelines will result in the masses of flowers brightening up your landscape in the spring.