Fragrant lavender (Lavandula spp.) supplies year-round garden interest, with aromatic flowers in summer and gray-green evergreen foliage. When you prune lavender plants, you encourage strong growth, help shape the plant and harvest the lavender for various uses. The small shrubs grow in U.S. Department of Agriculture plant hardiness zones 5 through 9, according to species and cultivar, 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.
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Prune Lavender Plants in Spring
New lavender plants need to be pruned in spring when new green growth has appeared. Spring pruning prevents flowering but encourages branching, allowing the new lavender plant to develop strong roots and a full framework of branches.
Before pruning, wipe the pruning shears with a cloth soaked in isopropyl alcohol to disinfect them. 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.
Deadheading and Harvest
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. To deadhead lavender plants, trim at the first set of leaves, leaving more of the stem than you do during regular summer pruning.
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.
Summer Lavender Shaping
Summer is the main time to prune lavender plants 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. To create the mounding shape, cut the outer stems a little shorter than the middle stems. 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. This can make the entire plant weaker. It's better to wait to prune until spring if you don't get it done in time in the summer or early fall.
Rejuvenating Woody Plants
Woody, overgrown lavender plants develop sparse foliage and may fall open, or split. Not only does this make the plant look less attractive, but it can also decrease the lavender plant's life. 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.