Azaleas are a beautiful, colorful addition to southern landscapes, and their popularity has led to massive breeding efforts to create new colors and cultivars with unique characteristics.
But, what happens when they stop blooming?
Azaleas stop blooming for four common reasons:
- The flower buds were pruned off
- Drought stress
- Freeze damage
- High pH
You can get azaleas to bloom again by pruning correctly, adjusting your irrigation schedule, or helping shrubs recover after a hard freeze.
Of course, there are other, less likely reasons for azaleas to have fewer blooms or stop blooming completely. But first, let’s discuss what an azalea is—and isn’t—because this plant is constantly confused with another popular landscaping shrub- the rhododendron.
Azaleas vs. Rhododendrons
Azaleas are a subspecies of rhododendron. Rhododendron is a genus in the family Ericaceae. Azaleas make up two subgenera of the Rhododendron genus (source):
- Tsutsusi is the subgenus for evergreen azaleas
- Pentanthera is the subgenus for deciduous azaleas
A “true” rhododendron is a member of the subgenus Rhododendron or Hymenanthes.
So, all azaleas are rhododendrons, but not all rhododendrons are azaleas. However, a true rhododendron is a member of a rhododendron subgenus, while an azalea is a member of an azalea subgenus.
Although it can be difficult to tell the difference between an azalea subgenus and a true rhododendron subgenus, there are a few distinguishing characteristics:
- Azaleas bloom in early spring, while rhododendrons bloom in late spring
- Azaleas have tubular flowers, while rhododendrons have shallow, bell-shaped flowers
- Azaleas have one stamen per lobe, while rhododendrons have two stamens per lobe
- Azaleas tend to have smaller, elliptical leaves while rhododendrons have larger, wider leaves
However, even seasoned botanists and landscape professionals can mistake the two, which can make it more difficult to figure out why your shrubs aren’t blooming.
Once you’re sure your shrubs are azaleas, you can move on to diagnosing problems with blooming.
Common Reasons Azaleas Stop Blooming
There are four common reasons for azaleas to slow down or stop blooming:
- Pruning off flower buds
- Drought stress
- Freeze damage
- High pH
Of course, poor soil conditions, poor lighting, and other environmental factors can influence blooming, but this would result in consistently poor blooms instead of a sudden decrease or halt during a given growing season.
Pruning off Flower Buds
The most common reason azaleas stop blooming is because the flower buds have been pruned off.
Most azaleas bloom in early spring, although new cultivars can bloom later in the year or twice in the same growing season. Within a few weeks of blooming, the shrubs produce flower buds for the next bloom.
If you prune after the flower buds have formed, you will end up pruning them off and reducing or eliminating the following blooming period.
If your shrubs look otherwise healthy with sporadic or no flowers, it is most likely due to poorly-timed pruning.
Another common reason azaleas may have reduced flowers is drought stress.
Although some cultivars do well in northern climates, most azaleas grow in hot, humid conditions in the south. An extremely hot, dry summer can cause a weak, shallow root system. The shrub will respond by diverting energy away from blooming and into surviving extreme conditions.
Evidence of drought stress includes wilting, dry foliage, stunted growth, and a dull color.
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Azaleas are sensitive to cold weather, and one of the most vulnerable parts of an azalea is the flower buds.
Temperatures below 25 degrees will cause root, stem, and flower bud damage. However, cold winds and dry winter conditions can cause damage even at warmer temperatures.
Young shrubs are more vulnerable than established plants. Azaleas in the deep south are more likely to suffer from a mild cold snap than plants farther north that are conditioned to cooler winters. As a general rule, unseasonably cold weather can damage otherwise healthy azaleas in any climate.
Evidence of freeze damage is mushy foliage, split branches, and damaged leaf/flower buds after a cold snap.
Pruning Azaleas for Maximum Blooms
The most common reason azaleas stop blooming is because they are commonly pruned at the wrong time. Most shrubs and trees are pruned in early spring or late fall. Gardeners who are not familiar with the unique requirements of azaleas tend to prune them at the same time as other landscape plants, which leads to accidentally removing flower buds.
Luckily, this is an easy mistake to fix.
Shrubs that have had flower buds removed divert energy into leaf and root production, so the plant may benefit from accidentally pruning out of season. If you know the lack of blooms is a result of pruning, avoid pruning completely for the year.
The shrub will produce new flower buds in early summer, and it should bloom the following spring. The flowers may be sparse, depending on how the shrub was pruned, but the flowers will indicate when it is time to repair any pruning damage done the previous year.
As soon as the blooms begin to fade, it’s time to pull out the pruners.
How to Prune Azaleas
Azaleas respond well to natural shaping as opposed to formal hedges. Excessive shaping will result in decreased flower buds, and takes away from the natural beauty of the shrub.
Follow the 1/3rd rule for pruning azaleas, and aim for a natural, open shape (source).
- Do not remove more than 1/3rd of the total plant material
- Prune long, leggy branches back to the main trunk (thinning)
- Shape healthy branches and encourage lots of flower blooms by cutting back a few inches of each branch (heading)
- Remove dead and damaged branches (these do not count towards the 1/3rd rule)
- Use hand pruners, not hedge trimmers, and prune each branch individually (hedge trimmers tear branches and result in decreased blooms)
Pruning correctly stimulates flower bud development. As long as shrubs are pruned at the correct time, pruning should result in a shrub overflowing with blooms the following season.
Shrubs that are old, damaged, poorly maintained, or planted in less-than-ideal conditions may benefit from rejuvenation pruning.
Plants naturally respond to severe stress with a strong reproductive stage. In other words, a plant that is subjected to severe stress through harsh pruning will respond with a lot of flowers in an attempt to create as many seeds as possible. This is a natural survival response that many growers take advantage of to encourage blooming and fruit production in landscapes and fruit trees.
Rejuvenation pruning also stimulates root and branch growth, but it is considered a Hail Mary. A plant suffering from poor soil conditions, neglect, or old age may not respond well to severe pruning, and you may eventually have to replace the plant.
Rejuvenation pruning is similar to annual pruning, except you remove up to half of the plant material. You should still aim for a natural, open shape, but try to thin out the shrub by cutting some branches back to the base.
After you prune, continue to follow an irrigation and fertilization schedule, as well as applying compost and mulch each spring. This will encourage the plant to respond to pruning with a surge of new growth and, hopefully, an abundant flower display.
Watering Azaleas for Maximum Blooms
Azaleas prefer moist soil conditions, but they are susceptible to root problems if they are watered too frequently.
Most azalea species prefer partial shade, which helps prevent excessive evaporation. However, extremely dry summers or cold, dry winters can cause drought stress and reduce flowering.
Established shrubs should be watered every two weeks, and only when the top few inches of soil is dry. If shrubs begin to show signs of drought stress, like wilting or dry foliage, increase watering to once per week.
Use compost and mulch to help conserve water and maintain an evenly moist soil profile. This is just as important as implementing a consistent irrigation schedule because it will prevent excessive evaporation and improve soil structure.
Watch for signs of overwatering, which can mimic drought stress. If plants are wilting but the soil is moist, you may be watering too often or the soil has poor drainage. Azaleas can tolerate a few weeks of dry soil, so if your shrubs are showing signs of overwatering, allow the soil to dry out completely before you begin to water again. You may have to remove excess mulch or landscape debris to encourage airflow to the root system.
Protecting Azaleas from Cold Weather
Some azaleas are more cold-tolerant than others, but all azaleas suffer from cold damage when temperatures drop below 25 degrees.
Deciduous azalea varieties are more cold-tolerant and are usually grown in climates where they can adapt to colder winters. Evergreen varieties, however, are more vulnerable to light frost and may show more significant damage during cold weather.
Cold weather can have three negative effects on flower buds:
- If ice crystals form on the plant, cells may freeze. This expands the cell to the point where it may burst, which results in mushy foliage or split branches. Flower buds are one of the softest, most vulnerable points on a plant during a frost or freeze.
- Cold, dry winds sap the moisture from foliage, buds, and branches. Dehydration prevents nutrients from reaching plant tissue, and the plant may conserve moisture within the trunk and roots as a survival response. Again, flower buds are the most vulnerable, and one of the first to die off in these conditions.
- Unseasonably early or late frosts and freezes can cause damage either before the plant goes dormant, or right as the plant begins to grow in the spring. During this period, flower buds are much more susceptible to light frosts and freezes because they aren’t protected by dormancy.
Of course, severe cold damage can affect the health of the entire shrub, which can cause reduced blooms and stunted growth. This is usually the result of a snow load breaking the branches or a deep freeze killing off parts of the root system.
The only preventative measure for extremely cold weather is mulch to insulate the soil and provide a physical barrier from snow and ice.
For routine cold-weather protection, the goal is to keep ice crystals and wind from directly affecting the flower buds and foliage. The easiest way to do this is with frost fabric or plastic sheeting.
Frost fabric is breathable, which helps avoid a buildup of moisture and prevents the plant from becoming too warm (which could leave the plant more vulnerable). However, it’s not as effective during hard frosts and freezes, and it can be more difficult to secure in high winds.
Plastic sheeting, or a tarp, is solid, which provides more protection from frost and wind, but may trap heat and moisture if it is left on the shrubs for too long. This is a better option during extremely cold weather, but it must be removed once the threat passes.
If your shrubs suffer from cold damage, prune off affected branches as soon as the plant breaks dormancy in the spring. This will help divert energy away from damaged branches and back into the healthy portions of the plant.
Managing pH for Maximum Blooms
Azaleas are an acid-loving plant, and if the pH is too high, it will suffer from nutrient deficiency and become yellow and stunted.
The pH level in soil cannot change drastically from year to year. In general, the pH is fixed unless you take steps to manipulate it with sulfur or lime.
However, certain mulches and management practices can change the pH and cause a decrease in blooms and overall health.
If you notice a gradual decline in the health of your azaleas, do a soil test that checks nutrient and pH values. Azaleas prefer a soil pH of 5.0-5.5 (source).
Soil pH affects nutrient availability. So, plants may show signs of nutrient deficiency or toxicity, even though there are plenty of nutrients in the soil. If the pH is too low or too high, it will tie up the nutrients and make them unavailable for the roots to absorb.
The first step in diagnosing potential nutrient deficiencies or toxicities is to look at the pH levels.
If the pH is too high, try one of the following products to lower it:
- Aluminum sulfate
- Pine needles (mulch)
- Pine bark (mulch)
Pine needles and pine bark help maintain low pH, but they cannot reduce the pH by more than a few decimal points. They are a good option if your pH is slightly high, but aluminum sulfate and sulfur are better options for creating a noticeable reduction.
If the pH is within the normal range for azaleas, it’s time to look at individual nutrient deficiencies.
While any nutrient deficiency or toxicity will affect the overall health of the plant, phosphorus deficiency is the primary cause of decreased flower production.
Standard N-P-K fertilizers contain phosphorus (the middle number), while promoting healthy leaf and root growth. Use a balanced fertilizer or find a specially-formulated azalea fertilizer to provide adequate nutrition and enhance blooming.
Azaleas are a beautiful, traditional landscape plant that adds an abundance of color to the southern garden. With regular maintenance and an understanding of their unique growth habits, you can create a dazzling display of radiant blooms.
For more information on general garden maintenance, read Active Composting vs. Passive Composting and Soil Conditioner vs. Compost: What’s the Difference?