Lavender plants need 3 years to hit maturity. They will grow healthier, bloom more profusely and live longer if you do a little annual pruning. Don’t be afraid of this tough love. Lavender plants left to their own devices will become woody and flowering will diminish. Start your plants off right.
First Year Lavender Pruning
The important thing to remember about first year plants is not to prune down into the woody part of the stems. If you prune too drastically, they might not regrow. Look for where the woody section turns to soft green growth and then prune about 2 - 3 inches above that. It can seem severe, but pruning off all that top growth strengthens the roots and gives you a bushier, more compact plant
Second Year Lavender Pruning
Your plant should be quite a bit larger this year, with more blooms. While the plant is in bloom, usually in mid-summer, gather up the flower stalks and once again prune the plant back to 2 - 3 inches above where the soft, green growth begins on the lower part of the plant. Don’t shear straight across. Follow the contours of the plant. You should wind up with a rounded mound. Don’t forget to clean up the sides, too.
Third Year Lavender Pruning
By year 3, your plant should be quite large and blooming with abandon. The best time to prune is just as the flowers are starting to open. The flowers will continue to open after you harvest them and you will be able to enjoy both their beauty and their fragrance in bouquets or however you plant to make use of them.
Since you did such a good job of creating a mounded shape in years 1 and 2, the plant is so full by year 3 that using your pruners is not the most efficient way to prune any longer. A small sythe or curved harvesting knife is a much better tool for this. Grab the flower stalks by the handful and slice them off at the base. Don’t try to do the whole plant at once. Just grab what you can hold.
When to Prune Lavender Plants
In frost free areas, your lavender plants may remain evergreen. You can prune at harvesting time and prune to shape in early spring.
Hardiness Zones 7 and Below
Winter is not kind to lavender plants. In areas with freezing winter temperatures, you should hold off doing any hard pruning to your lavender plants until you see new growth starting, in the spring. The top growth will serve as insulation, keeping the crown and roots of the plant protected from repeated freezing and thawing.
Don’t wait too long to prune, though. You should see the new growth by the time the tulips are blooming. If you wait longer, you risk cutting off the flower buds that are forming.
There will probably be some winter die back, but if you wait until the new growth starts, you will be able to see which stems are dead and can be pruned out.
If you get a second flush of blooms in the fall, you can go ahead and cut them back. This will remove some of the top growth, but you don’t want all those flower stalks weighing the plants down.
The one thing to look out for here is wet soil. If you have a mild, but wet winter, check your lavender plants to make sure the tops are not holding excess water, which can cause the crowns to rot. You never want your lavender to be sitting in wet soil, which will rot the roots. Make sure it is growing in a well-draining site to begin with.
Lavender is not the easiest plant to grow in most areas, but your best bet at success is to get your plants well established early.