Allen D. Owings, Gill, Daniel J. | 8/7/2011 6:16:16 AM
Azaleas are spring showoffs, even though some newer varieties now bloom in other seasons. Most of us may not realize that azaleas represent the main nursery crop grown in many states in the southeast and along the Gulf Coast. In Louisiana, they represent seven percent of all nursery plants grown.
With the introduction and more common use of azaleas that bloom in other seasons, such as the increasingly popular Encore azaleas, it’s not unusual to see azaleas blooming during the late summer, fall and winter. In south Louisiana, it is possible to have some of these multi-seasonal-blooming varieties with significant flowering for 6-8 months of the year.
No other shrub in the landscape can beat azaleas for flower power when they are in full bloom. Although the floral display may be relatively short with many of our traditional azaleas, such as the Indica azaleas, it ensures the continued popularity of this time-honored Southern shrub.
Many factors play a role in the success or failure of an azalea planting in a landscape. These issues include planting time, sun exposure, soil pH, bed preparation, planting techniques, irrigation, variety selection and pruning. We will briefly discuss each of the factors and provide some recommendations that are considerable applicable in our hardiness zone area (USDA hardiness zones 8 and 9).
WHEN AND WHERE TO PLANT
Azaleas can certainly be planted in the spring. This is, of course, when garden centers have the best selection and is the time of year when gardeners see azaleas in bloom. (Did you know that many independent retail garden centers have 50% of their income for the year in the two peak months of the spring sales season?) Before purchasing azaleas, make sure you ask what the mature size of the plants you intend to buy will be. Depending on the variety, azaleas may mature at less than 2 feet up to 10 feet tall. Don’t purchase a type of azalea that will grow too large for the spot where it will be planted.
Spring-planted azaleas may take a little longer to become established then those planted in fall or winter. Fall and winter months would be the best time to plant. Fall and winter planting encourages root growth before spring bloom and shoot growth commence. Summer planting really should be avoided by most gardeners, although you can be successful planting at that time by providing extra care (primarily watering).
Many azalea varieties will tolerate full sun if provided with adequate moisture. Generally, however, azaleas grow best when they receive some shade during the day. Four to six hours of morning sun provided by an eastern exposure is considered ideal. Azaleas tend to have sparse foliage, look leggy and bloom poorly when planted in too much shade. If grown in too much sun, azaleas may wilt constantly during hot, dry weather and scorch on their leaf edges. Western sun exposure during summer and into early fall is very difficult on azaleas.
Azaleas require good drainage but also need an even supply of moisture. They will not thrive in a location that is constantly wet or constantly dry. Uniformity in soil moisture is important for good azalea growth and establishment in a landscape setting. Consider soil texture and soil structure of the native soil. Amending with pine bark or some other organic material will probably be needed.
HOW TO PLANT
Arrange the azaleas in the bed while they are still in their pots to get the spacing and arrangement right. When you get ready to plant and take the plant out of the pot, you may see a very dense network of roots around the outside of the root ball. This is not uncommon in container-grown plants. Use a knife to vertically cut into the root ball in several places, or use your fingers to pull apart the root ball and loosen it up. This will encourage the roots to grow out into the surrounding soil and increase the plant’s chances of survival. Do not do this if planting in the stressful summer months.
You should always plant azaleas so that the top of the root ball is at or slightly above the soil level in the bed. Do not plant them too deep! In addition, keep in mind that azaleas are shallow-rooted and benefit greatly from mulch. As soon as they are planted, mulch the bed with about 2 inches of pine straw, leaves or pine bark.
Azaleas prefer a moderately acid soil. Usually, the most ideal growth and nutrient availability occurs at a soil pH of around 5.5. If the soil in your garden is alkaline, apply ground sulfur or copperas (iron sulfate) during bed preparation according to package directions to help make the soil in the bed more acid. Don’t guess about soil pH. Conduct a soil test. All land-grant universities have soil testing labs where you can get this done. In beds where azaleas are currently growing, use copperas or a commercial soil acidifier if the pH needs to be lowered.
FERTILIZING AND PRUNING
While newly planted azaleas should not be fertilized, azaleas already growing in the landscape may be fertilized as soon as they finish flowering with a general-purpose or acid-loving plant food following package directions. If the leaves at the ends of the branches are yellowish-green with green veins, they need iron. Treat them with chelated iron, available in such products as Liquid Iron, and acidify the soil in their bed with copperas or a liquid soil acidifier.
As flowering finishes, evaluate your azaleas for needed pruning. April and May are good months to trim your bushes, but only do it if it is necessary. Generally, a little shaping is all that is required. Controlling size is a common reason for pruning, especially if large growing varieties were planted where smaller ones should have been used.
You should begin to manage the size of your azaleas when they reach the maximum desirable size. Unless you are trying to create a formal clipped hedge, avoid shearing azaleas with hedge clippers as this destroys their attractive natural shape. It is better to use hand pruners to remove or shorten selected branches to achieve the desired shape and size.
First, identify the tallest or widest shoots or branches on a bush that is too large. Use your hand pruners to shorten these branches. Instead of making cut at the edge of the bush, prune the branch down within the shrub. When the shortened branch sprouts, the new growth will be inside the shrub creating a thicker, fuller plant. And the new growth will not immediately stick out above the rest of the bush – something that commonly happens if pruning cuts are made just back to the edge of the bush or when azaleas are sheared. Keep cutting back the tallest and widest shoots until the shrub is the proper size. You may continue to prune occasionally as needed using this technique into the summer up until late June, early July at the very latest. After that, the chances increase that you will remove flower buds when you prune. Alternate-season-blooming azaleas, such as the Encores, have a shorter window of opportunity, and pruning on them should done as soon as the major spring-blooming period is over.
We have not yet mentioned much about irrigation. How much water to apply? When should plants be irrigated? How frequently? All of these are questions that are hard to provide specific answers for because natural rainfall must be factored in. Irrigation is done to maintain soil moisture when adequate rainfall is not occurring.
Supplemental irrigation is far more likely to be needed when dry spells occur during the hot summer and early fall (May to October) than during the moister, cooler winter months. When needed, enough water should be applied during irrigation to thoroughly wet about the upper 4 to 6 inches of soil. It is better to water azaleas (and other landscape shrubs) thoroughly, occasionally rather than lightly, frequently. Mulches are extremely useful in helping to maintain soil moisture.
Newly planted azaleas in their first year or two after planting require more attention to watering than established azaleas. Monitor newly planted azaleas carefully their first summer in the ground. During dry, summer weather, newly planted azaleas may need to be watered twice a week. Older, established azaleas will be more resilient, but they should be thoroughly irrigated at the first sign of slight wilting.
Drip-irrigation systems and soaker hoses are useful in applying sufficient water slowly over time. This allows the water to penetrate deeply into the soil. These methods also help keep the foliage dry, minimizing possible fungal problems like leaf spots. Sprinklers also work well. All methods should be used only when necessary and be left on long enough to thoroughly irrigate the planting. Hand watering usually does not provide a deep, thoroughly irrigation, and the other methods of watering are generally preferred.
Frequent, light irrigation only wets the upper part of the soil and leads to shallow root systems. Azaleas whose roots have been encouraged to grow close to the surface are more prone to drought stress than azaleas that have been watered properly. However, proper watering for a growing season or two will encourage a deeper, healthy root system and correct the situation.
Water quality is also an issue in some areas. Municipal water supplies or well water high in bicarbonates (also called alkalinity), pH and/or sodium are not ideal for azaleas. This is generally more of an issue for azaleas growing in containers than azaleas growing in beds.
Azalea lace bugs are the leading pest of azaleas in the southeastern United States. They are active beginning in February and will continue to be active to varying degrees through the fall. The lace bug attacks azalea foliage, causing it to become stippled with small, white dots. Lace bugs live on the underside of the leaves, and the lower surface of the leaves will have dark brown spots. There are several generations of these pests per year, but most damage from lace bugs seems to occur from the early generations in spring. Inspect the healthy, new growth of your plants regularly in late winter through midspring. If you have had lace bugs before, you will have lace bugs again. Acephate, horticultural oils and the Bayer Advanced Garden insecticides do a good job controlling these pests.