Leaf drop is not an event put on exclusively in the fall by deciduous trees and shrubs. Evergreens drop leaves, too, just not so conspicuously. Some of our signature Southern evergreens regularly shed their older leaves in the spring.
Broadleaf evergreens drop old interior leaves that have been shaded by new growth. Typically, old leaves turn yellow and brown, and then fall off. Depending on a plant’s species, evergreen leaves generally last one to six years. Evergreens naturally shed some percent of their leaves every year, while branch tips and younger leaves remain green. Leaf drop is often concurrent with or immediately follows new growth.
Southern magnolias and many hollies are among the broadleaf evergreens that drop their leaves in the spring. For example, hollies shed their year-old leaves during their second year, magnolias drop their old leaves during bloom time and continue to drop a few leaves all summer long. Other evergreen shrubs shed their old leaves in summer or early fall.
Needle evergreens, local pines for example, typically hold their needles for one to three years before shedding them in the fall and winter. Yews retain their needles for three to five years with some percent of needles turning yellow each year and dropping in late spring or early summer. Arborvitae sheds its old interior leaves in the fall.
It is useful to become familiar with your evergreens’ normal leaf drop and renewal cycle. That will make it easier to pick up on abnormal shedding caused by extreme heat or cold, wet or drought, nutrient deficiency, insect infestation, disease and pollution.
Weather extremes and tough environmental conditions stress and weaken plants. That makes them more susceptible to insects and disease. Even if you know the cause of untimely or excessive leaf drop is environmental, it is smart to check plants for disease and insects.
After a protracted wet period, look for mildew and other fungal diseases on your evergreens. The infected leaves fall off, but plants still need to be treated for the fungal disease. Be sure to clean up and dispose of the contaminated leaf litter.
An infestation of sap-feeding insects can suck the life out of a plant, causing leaves to yellow and drop off. If you find sooty mold on leaves, it indicates that the plant is infested with common sucking insects like scale, spider mites, white fly or aphids. Sooty mold forms on the secretions from the insects. The pests need to be eliminated before the mold can be eradicated.
Evergreen azaleas grow spring leaves, which drop in the fall. During the summer, the plants grow leaves, which often remain for several years before they are shed. It is smart to monitor azaleas for lace bugs and spider mites, both of which cause leaf damage and leaf drop. For lace bugs, watch for a mottled, bleached-looking leaf surface with brown spots on the underside and, of course, stay alert for the tiny lacy-winged insects. It’s easier to identify spider mites by the presence of their webs than it is to see the tiny mites themselves.
Azaleas and gardenias are both acid-loving plants that are subject to iron chlorosis — yellow leaves with veins that stay green — if the soil pH is too high. An application of iron in a foliar spray is a quick fix during the growing season, but a soil test is necessary to find out how to correct the pH.
It is normal for older leaves to turn yellow and drop off gardenias in the early spring before new growth starts. Pay attention to chlorotic leaves at other times of the year. White flies, tiny white-winged insects, are the most common pest that attacks gardenias. If a white cloud lifts from your gardenia when you shake it, you have white fly infestation. Again, sooty mold growing on the surface of leaves is an indicator that the plant is under attack by a sucking insect. Monitor gardenias for aphids and mites, too.
Cyclical leaf drop is natural among evergreens, but be on the lookout for insect pests, disease and nutrient deficiencies that cause unnatural leaf drop.
Reach DEBBIE MENCHEK, a Clemson Master Gardener, at firstname.lastname@example.org.