Pruning Rosemary and Lavender
Question: I have some rosemary (Rosmarinus officinalis ‘Arp’) and English lavender (Lavandula angustifolia ‘Hidcote’), which have some dead stems and branches, perhaps due to the harsh winter weather. About half of the stems are affected. Will they come back? Should I trim off the tips, prune out the dead branches, or do I need to replace the plants?
Known for their beauty, scent and culinary uses, both rosemary and lavender are favorites of many gardeners. Both are native to the Mediterranean area and thrive in warm dry summers and mild winters. Periodic careful pruning helps make these plants less susceptible to disease, pests and winter damage. Pruning also will encourage new growth, shape and control plant size and increase the yield of the plants. The best strategy to avoid losing your rosemary and lavender plants due to winter injury is to take care of them all year long. Central Virginia’s clay soil, wet springs and summer humidity can make growing rosemary and lavender difficult. But, if these herbs have been planted in the right place, and maintained appropriately, recommended pruning techniques can protect your plants for years to come.
Rosmarinus officinalis ‘Arp’ is a tender perennial in Central Virginia (plant hardiness zone 7), but can live for many years with proper care. This evergreen shrub in the Lamiaceae or mint family, has dark green needle-like foliage and can reach 4-6 feet in height and 3-4 feet wide. Rosemary needs at least 6 hours of full sun per day and well-drained, loamy soil with a slightly acidic pH of 6.0-7.0. If the soil doesn’t drain well, the plant will be susceptible to root rot.
Spring and summer pruning. Cut back the plant to about 1/3 of its height in late spring or early summer to control shape and size of the rosemary. Trim the succulent green stems, not the woody bottom of each stem to avoid limiting new growth. Trim back overgrown stems anytime in the summer to maintain the plant’s shape and size. Rosemary needs 6-8 weeks for new growth to harden off in the fall before the first hard frost, so stop pruning in early September.
Pruning for winter damage. Cut back the dead and winter-injured branches and stems to the nearest healthy portion in late winter just before new growth appears.
Lavandula angustifolia ‘Hidcote’, commonly known as English lavender, is an herbaceous perennial that also belongs to the Lamiaceae family. It is good for small spaces, with 6-8 inch stems, 12-20 inch tall, pretty dark blue flowers and a sweet aroma. Lavender needs 6-8 hours of full sun, well-drained soil, a soil pH between 6.5-7.5 and little fertilizer. It grows well in rocky, sandy, dry soil, on slopes or planted in mounds to provide drainage. A mulch of pea gravel or white rock is preferable to wood mulch which retains moisture and can cause root rot.
Spring pruning. Prune back new growth after blooming each year to keep it from getting scraggly and to encourage a second bloom later in the season and side branching. Don’t cut into the woody stems.
Fall pruning. Prune again in the early fall 4-6 weeks before the first hard frost so it has time to recover. Cut plant back by 1/3 but make sure to leave at least 3 sets of leaf nodes on each stem. Keep plants compact to reduce damage from cold, snow and frost. English lavender can be protected from harsh winter weather with a protective cover, straw, oak leaves or evergreen boughs.
Pruning for winter damage. Prune out damaged and dead branches and stems in late winter/early spring after new growth begins on the stems. Don’t cut back dead-looking stems with new growth at the base or that bend to the touch; these stems and branches are dormant but still alive and will produce new growth. Dead branches will break off easily. When in doubt, be patient and wait to see if new growth emerges. If part of a branch is dead, trim back to healthy sections with live buds.
Other tips for growing rosemary or lavender. Remove dead, diseased or damaged parts of the plant at any time during the year to keep the plants healthy. And remember to use clean, sharp pruning shears to promote healing and help prevent disease and injury to the plant! Cover the plant with a layer of mulch or install a wind break to protect it through winter.
Prune or replace?
With proper pruning year-round, it is definitely possible to keep established rosemary and lavender plants thriving, even when harsh winters cause dieback of part of the plants. Both of these types of plants live about 10 years. So, if your plants are close to that age, you may want to replace them. Pick a good site, get a soil test and follow recommended soil and planting guidelines, and you are well on your way to watching your herbs flourish. Plant tender perennials like rosemary on the south side of a house or building for added protection. Another way to avoid winter damage entirely, is to grow rosemary in containers that can be brought inside during the winter or keep rosemary and lavender plants indoors all year.
Happy herb gardening!
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