While most lavenders need dry air and perfect drainage to thrive, fernleaf lavender (Lavandula multifida), part of the Plants for Texas line, is one of the few that grows well in humidity, including coastal areas with frequent fog. Fernleaf lavender features fragrant, deeply cut gray-green foliage and blooms with spikes of medium purple flowers all summer long. This lavender species is treated as an annual in much of the country, but does require regular pruning in U.S. Department of Agriculture plant hardiness zones 8 through 10.
Fernleaf lavender grows about 18 inches tall and 2 to 3 feet wide. The flower spikes, which occur in clusters of three, float 10 to 14 inches above the slightly fuzzy foliage on wiry stems. It grows in full sun and can be evergreen in frost-free areas. Where it is annual, simply pull it out and replace it each year. Take cuttings in the fall to propagate plants for next spring over the winter.
Fernleaf lavender is a subshrub, which means it develops a woody base from which fresh new growth emerges. It won't grow back from the roots if it is cut all the way to the ground. Prune back dead growth in spring after new growth has begun, making the cuts 1 to 2 inches into green growth to tidy the look of the plant, ensuring green remains below the cut. Waiting to prune until buds swell and leaves start to emerge lets you prune more confidently, eliminating only damaged stems. Fernleaf lavender suffers cold damage below 10 degrees Fahrenheit and when winters are particularly wet.
Cutting back the wiry stems of fernleaf lavender blooms as the flower spikes die back keeps the plant looking good and encourages the plant to produce another round of the fragrant, purple flowers. Removing the stems about 1 inch into the foliage keeps the plant from becoming leggy and splitting open as the season progresses. When grown strictly as an annual, cut back fernleaf lavender each time blooms fade until frost. Where the plant is perennial, stop cutting six to eight weeks before your usual first-frost date to avoid damage to tender new growth over the winter.
Every time you prune fernleaf lavender, or any plant, use sharp pruning tools sized to the stem you need to cut. Bypass pruners, easily cut stems up to 1/2 inch in diameter, and are appropriate for most fernleaf lavenders. Wipe down the blades of your pruners with household antiseptic cleaner before each use and between cuts when working with a diseased plant to decrease the chance of spreading disease.
- Plants for Texas: Lavandula Multifida - Fern Leaf Lavender
- The New Western Sunset Garden Book; Editors of Sunset Magazine
- Fine Gardening: Pruning Subshrubs
- San Francisco Department of Public Works: San Francisco Sidewalk Landscaping Recommended Drought-Tolerant Plants
- Royal Horticultural Society: Lavender
- Washington State University Extension: Myth of the Cloroxed Clippers