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Missouri Environment & Garden


David Trinklein
University of Missouri
Plant Science & Technology
(573) 882-9631

Azaleas for Early Indoor Color

David Trinklein
University of Missouri
(573) 882-9631

Published: March 4, 2022

minute read

pink flowers in white pot

credit: www.teleflora.com

Flowering potted azaleas (sometimes called florists' azaleas) are available for use as indoor plants throughout the year. However, it is during late winter and early spring that they are more commonly found at retail outlets. In addition to being a bit less expensive at this time, they provide a welcome and colorful prelude to spring. Azalea flower color ranges from red though many shads of rose, pink, salmon and white.

pink and white ruffled flower pedals

Although the petals of azaleas might seem fragile, a blooming plant will provide several weeks of indoor color, if given proper care. Normally, purchased plants have some open flowers along with a goodly number of unopened buds. The latter help to extend the display of color even longer.

Good light, careful watering, and cool temperatures are essential for azaleas to flourish in the home. Watering is particularly critical. Never let the growing medium dry out, but do not drown the plants. Today, most potted azaleas are produced in a growing mix which is primarily organic matter such as peat moss and may not contain any soil. Even if soil is included in the growing mix, it usually is in very small amounts.

Azalea roots are fine and delicate. Many are located along the outer edges of the pot, which is the first area to dry. Excessive drying of a highly organic growing medium causes roots to be lost quickly. The frequency with which water is needed depends on a number of factors including pot size, indoor temperature, humidity and light intensity. However, in an average home, a thorough watering every two to three days should be adequate.

One of the best ways to water a plant growing in a highly organic mix, especially if it may have become somewhat dry, is to submerge the pot in a bucket full of water. If the pot was very dry, it may tend to float. If this happens, allow it to remain until it somewhat settles, or anchor the pot with a weight. Allow the pot to remain submerged until bubbles stop rising. The top portion of the plant (foliage and flowers) should remain above the water and not allowed to get wet. After five to ten minutes, remove the pot, allow excess moisture to drain, and return the plant to a saucer in its original location.

One of the easiest ways to determine the need for water is to test the weight of the pot as you lift it from its saucer. Compare this weight with the weight of the pot after it was last watered, drained and returned to the saucer. If the pot begins to feel fairly light, even though the surface of the growing medium still feels slightly moist, it probably is time to water. If plants become too dry, flowers will wilt first and their life will be shortened. However, if drying is not too far advanced, they normally will recover.

In order to determine what to do with a potted azalea after flowering is finished, some knowledge of the type of azalea it is will be very helpful. Unfortunately, most azaleas chosen to be forced as potted flowering plants were selected for reasons of than their ability to tolerate cold temperatures. Therefore, we should assume they are not reliably winter hardy in our climate. However, it still is possible to rebloom these azaleas as potted plants in future years. The requirements for reblooming are somewhat complex and fairly exacting.

After flowering is complete, the plant should be placed in a sunny window in a cool room in the home. A hobby greenhouse can make the process much easier. Azaleas that have finished flowering and are to be kept for subsequent reblooming do not always need to be repotted. However, if the plants appear "top heavy" (large plant in a small pot), repotting may be advisable. Commercial mixes for acid-loving plants are available, or one can formulate their own mix. A medium consisting of three parts of (raw) acid peatmoss and one part of garden soil works well. When repotting, take care not to disturb the existing root ball. Gently fill and pack fresh mix around existing roots to fill the larger pot.

In April, after the danger of any cold weather other than a light frost has past, plants may be moved outdoors. Place them in a lightly shaded area where they will remain for the summer. Pots can be sunken into the soil to prevent tipping, but do not forget to water them. During summer months when water loss is extreme, daily watering of the plants often is necessary.

As plants grow throughout the summer, little needs to be done except for watering and fertilizing with an acid reaction fertilizer. Water soluble fertilizers blended for acid-loving plants are ideal and help to prevent iron chlorosis. If foliage becomes yellow or chlorotic, iron uptake may be limited. This can mean root loss from too much or too little water. It can also result from a pH that is too high (soil too alkaline), or it may actually be a lack of iron in the soil. Apply a chelated iron or iron sulphate to correct the situation. Ammonium sulphate fertilizer also helps to lower the pH and maintain the acidity of the soil. Apply about one half teaspoon each of iron sulphate and ammonium sulphate to one quart of water. Apply this to the plants about every two to three weeks, while using a complete houseplant fertilizer in between.

To keep plants compact and attractive, clip back long shoots as they form. Plants should be allowed to remain outdoors as long as possible in the fall. While azaleas cultivars selected for forcing can tolerate a light frost, they should not be exposed to prolonged cold weather for fear of flower buds that are forming will be killed.

For potted azaleas to develop buds that will flowers the following winter, they must be vernalized. The latter involves subjecting plants to cool temperatures in order to induce flower bud formation. To accomplish this with azaleas, plants should be brought back indoors when the weather cools and kept in bright light in a cool room where the temperature is about 40 degrees F., or slightly below. About two months (e.g., November 1 through January 1) of cool temperatures are required to induce flower bud formation. Do not fertilize plants during this period and water enough only to prevent wilting. After vernalization is completed, plants can be moved to a slightly warmer location in the home which should prompt the flower buds to open.

If the potted flowering azaleas purchased are known to be reliably winter hardy at our latitude, the reblooming process is much easier. Simply plant the azaleas outdoors in April or May into beds in a shady location with soil that is high in organic matter. A mulch and summer water is important since, as previously mentioned, azaleas have a very fine and fairly shallow root system. Acid soil and excellent drainage are necessary also. Nature will take care of the required vernalization for you.

Finally, a word of caution is in order. Although they are beautiful flowering plants, all types and all parts of azaleas are considered poisonous. Therefore, proper precaution should be taken to keep plants out of the reach of children and pets.

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REVISED: March 9, 2022