Why Does a Lavender Plant Turn Yellow?
Lavender (Lavandula angustifolia) offers the home landscape a delicate yet abundant delivery of a colorful summer bloom in purples and pinks on gray-green foliage. Unfortunately, when foliage begins to turn yellow as a symptom of an underlying problem, its complementary contrast with the purple flower tones makes the issue that much more conspicuous. Examine lavender plants regularly for abnormalities, and address problems as they occur for continued healthy growth.
Avoiding problems with yellowing begins with optimal plant care. Healthy, strong lavender plants have a greater chance of escaping and recovering from problems that lead to discoloration than poorly maintained plants. Lavender grows best in areas of the home landscape that provide full sun exposure, as shaded conditions lead to poor development. This herbaceous plant thrives in light, moist, well-drained soil with a pH of 6.4 to 8.2. Lavender performs best in U.S. Department of Agriculture plant hardiness zones 5 to 9.
Simple cultural maintenance issues are often the only culprit in the yellowing of lavender plants, particularly when plants do not receive appropriate amounts of moisture and nutrients. Gardeners should irrigate the plant when the top layer of soil feels dry to the touch. Though lavender plants tolerate periods of drought, watering too frequently or infrequently leads to yellowing foliage. In addition, weeds that crop up often win the battle in the competition for nutrients necessary for plant function. To avoid weed development and to help conserve moisture, gardeners should mulch by laying a 2- to 3-inch layer of compost or bark on the soil surrounding lavender plants without pressing it against stems.
Plant yellowing is often due to pathogenic disease. Lavender is particularly susceptible to a fungal disease called phytophthora root rot. Caused by pathogens of the Phytophthora species, this disease proliferates under wet conditions. The soil-borne disease attacks roots, leading to above-ground symptoms, such as wilted, yellowed foliage that may occur on one isolated area of the plant before spreading. Due to decay, roots become near black in color and mushy and wet. Plants may quickly decline and die.
Maintaining good plant health may be the best defense against root rot disease. Providing proper drainage is essential; home gardeners may mix organic content, such as compost, into the top layers of soil to improve drainage. Though the pathogens are soil-borne, they may spread on water, wind and infected tools, such as pruning shears. Maintaining sterilized gardening equipment and avoiding overhead watering contributes to root rot control within the garden. To further prevent the disease, growers may combine cultural efforts with an application of a fungicide with the active ingredient fosetyl-al. Plants with an existing infection should be removed and destroyed along with plant debris and neighboring plants treated with preventive measures.
- Ohio State University Extension: Lavandula Angustifolia
- Cornell University Gardening: Lavender
- Utah State University Cooperative Extension: English Lavender in the Garden
- University of California Statewide Integrated Pest Management Program: Overwatering
- University of Wisconsin Cooperative Extension: Growing Lavender
- University of California Statewide Integrated Pest Management Program: Phytophthora Root and Crown Rot in the Garden
- University of Illinois Extension: Root Rot of Herbaceous Plants
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