Richard Bogren, Owings, Allen D. | 2/7/2015 2:08:05 AM
News Release Distributed 02/06/15
By Allen Owings
LSU AgCenter horticulturist
HAMMOND, La. – One of the most widely planted landscape shrubs in Louisiana is the azalea. Dwarf, intermediate and the larger-growing Southern Indica varieties are common in our landscapes.
Many times from the late fall through winter, you may notice azaleas with reddish or purple foliage, yellow foliage, spotted foliage and just overall “poor-looking” growth. Sometimes, plants will be partially defoliated even though the vast majority of azaleas we commonly grow are evergreen.
These symptoms normally are descriptive of an “end-of-the-growing-season” look. Some azaleas, like the popular Fashion variety, have bronzy to purple-looking foliage in the winter. All evergreen azaleas go through a stage when old foliage is being lost and new foliage is emerging for spring.
Although yellow foliage could be an indicator of just old growth, it also could be caused by a leaf spot fungus, a lack of nutrients in the soil or improper soil pH.
Azaleas prefer a part-sun planting location. Plants in more shade than sun normally have thinner foliage in wintertime.
Azaleas are normally fertilized in spring after flowering is complete. You may also fertilize in late summer, but this application needs to be at a lower rate and should not be done after early September because a late fertilization can increases cold damage to plants during winter. When fertilizing azaleas, use a three-month, slow-release fertilizer for best results.
Azaleas can also benefit from applications of an iron fertilizer once a year in many cases. This would primarily be when azaleas are growing in soil with a higher-than-recommended pH. Azaleas prefer an acid soil with a pH between 5.0 and 5.5, and many azaleas in Louisiana are growing in soil with a higher pH. You can use sulfur fertilizer products to lower soil pH, but this should only be done following directions found in an LSU AgCenter soil test recommendation.
Irrigation management is important for azaleas. Sometimes the foliage problems we see may be related to too much water or to a root system problem. If azaleas were over-watered during summer, the plants could be suffering from fungal organisms in the soil that attack and damage or kill the roots. Dead roots cannot absorb water, and when the upper part of the plant is deprived of the water it needs, it withers and dies.
Azaleas prefer uniform soil moisture and generally need about 0.75 to 1 inch of irrigation in a well-drained bed during summer months when rainfall is insufficient.
LSU AgCenter faculty are seeing cold damage on azaleas this year as a result of the early freezing conditions we had in November. Cold can cause internal damage that affects the plant’s circulatory system. In other words, it interferes with the plant’s ability to move water through the branches and into the leaves. Although it occurs in winter, branch death often doesn’t appear until warm weather arrives. Cold-damaged azaleas will show numerous splits and cracks in the bark and even peeling bark. These symptoms are often sectional as well, with some parts staying green and some dying.
Azaleas are popular and an easy plant to grow in Louisiana landscapes. Just look around at old landscapes throughout the state and observe how well azaleas have traditionally performed. They do best when the soil is acid, when they are grown in more sun than shade, when irrigation is properly managed and when plants receive adequate nutrition.
You can see more about work being done in landscape horticulture by visiting the LSU AgCenter Hammond Research Station website. Also, like us on Facebook. You can find an abundance of landscape information for both home gardeners and industry professionals at both sites.