Fragrant lavender (Lavandula angustifolia) supplies year-round garden interest, with aromatic flowers in summer and gray-green evergreen foliage. The small shrubs grow in U.S. Department of Agriculture plant hardiness zones 5 through 9, where they thrive with very little maintenance beyond pruning. The right time and method for pruning depends on the age of the plant and the type of trim it needs.
New plants need to be pruned in spring when new green growth has appeared. Spring pruning prevents flowering but encourages branching, allowing the new lavender to develop strong roots and a full framework of branches. Before pruning, wipe the shears with a cloth soaked in isopropyl alcohol to disinfect them, and then disinfect the shears each time you begin pruning a new plant. Cut back the stem tips by 2 to 3 inches, lightly shaping to maintain an even, rounded shape.
Lavender may flower a second time if you prune off the old flowers after the first flush of summer blooms. Prune off the flowers a second time in late summer if the plant flowers again. Deadhead after the flowers open and begin to wilt if you want lavender blooms in the garden. For harvesting and drying, cut off the flowers when only two or three buds on the flower spikes have opened. Trim out the spikes with disinfected shears, cutting the stem so the cut end is inside the main bush and not visible. For harvesting, tie the harvested spikes together in bundles and hang them in a dark, dry area until the buds are completely dry.
Main pruning occurs in summer, after the flower harvest. Cut back up to one-third of the leafy section of the stems, shaping the lavender into an evenly rounded mound as you prune. Avoid cutting into the woody stem bases. Lavender will not regrow from the lower stem sections, so cutting into wood will leave bare spots in the bush and weaken the lavender. Although summer, after the plant flowers, is the best time to prune, you can prune into late summer or early fall. However, avoid pruning in late fall because frost can damage the new growth encouraged by pruning.
Woody, overgrown lavender plants develop sparse foliage and may fall open, or split. In most cases replacement is the best option, but you may be able to rejuvenate the lavender with careful pruning. Prune for rejuvenation in spring when new growth begins showing on the stems. Cut back all the green stems to within 1 inch of the woody portion at the base, but don't remove the green completely. The lavender may produce fuller growth in response.