A tough plant for sunny dry spots and one of the longest-blooming tough semi-shrubs around, lavender (genus Lavandula) would find a place in most sunny gardens even if it didn’t have such a heavenly scent.
There’s more good news, too: lavender is easy to prune, and when you do it, you’ll be covered for the rest of the day in those aromatic oils. This is one of the few gardening tasks that is a good idea to do right before a hot date!
Lavender: a Semi-Shrub to Tame
Did that term “semi-shrub” in the first sentence catch your eye? Lavender is a semi-shrub, a plant that looks like a perennial because most of it is soft green growth, but which will turn to wood in the parts that are a few years old. Knowing this is going to help you prune your lavender.
Deep at the center of the mound that your lavender likes to grow into, your lavender plant is trying to turn to wood. One goal of pruning lavender is to slow down the formation of wood. Here is why:
- Lavender wood is very weak and prone to splitting under snow, ice, and water-rot.
- Unlike many true shrubs and trees, lavender wood that has formed usually does not rejuvenate when pruned, but simply dies.
- Old wood will stop producing new shoots, or will produce spaced-out shoots, destroying overall appearance.
Pruning heavily every year will help slow down the formation of wood and extend the vigor and lifetime of your plant. The tips below will help you make the most of a yearly pruning.
General Tips For All Species and Varieties
Start pruning young. If you begin by pinching tips of new growth when the plant and its growth is very young, it will respond vigorously with dense branching that helps form a good shape and a lot of blooming growth to work with later. Waiting to prune lets the plant form older, eventually woody growth that responds less well to pruning.
Timing: the best is after flowering, but lavender is forgiving. All lavenders bloom on the stems that grew this year. This means that pruning can be done any time from after completion of flowering until mid spring without sacrificing that year’s flowering. Pruning late in summer to fall opens air circulation in time for the threats of winter frost and snowdrop. Pruning in spring can delay flowering but is a good time to take down dead, winter-killed parts and shorten growth to the fat, vigorous buds. If you have the time, pruning twice a year is good.
Prune established plants heavily, back at least 1/3. Lavender in full sun can be expected to grow vigorously each year, and vigorous growers need a little yearly punishment to stay vigorous. With your hand pruners or pruning shears, aim to snip back all shoots at least 1/3. Shears are less accurate, but save time and are a necessity for a lavender hedge.
Go heavier on older plants, but don’t cut down to leafless wood. As mentioned before, you can’t rejuvenate older plants by cutting into old wood, but you can try to rejuvenate them by pruning to points just above the wood. A good rule of thumb is to count to the third node above the woody part and then cut just above it. If you are lucky, all three nodes and some hidden nodes buried in the wood will wake up and grow for you.
Beware Woody Growth and Winter
Your main goal in pruning lavender is to prepare it for the ravages of winter by reducing its size, weight, and density. This is a great reason to prune in autumn, just before frost and winter arrive.
As with so many plants, the thing to be worried about in pruning lavender is being too worried to try! Not pruning lets a plant get large and dense, forming nooks and crooks that trap water. Here are the risks:
- In summer, trapped water promotes rot in lavenders weak stems and wood.
- In late autumn, trapped water becomes an early frost, ending the growing season early.
- In winter, trapped water can freeze, easily splitting out woody parts.
- A dense plant or one with sprawling wood is a weak target for snow load, which will deform or break plants.
Pruning Your Particular Variety of Lavender
The above tips—plus your own boldness and instincts!—will get you pretty far with pruning lavender.
Do you know what kind of lavender you have, or could you tell with a little help? Do you want to fine-tune your pruning to get the most out of your specific type of lavender? Tips for pruning specific types of lavender will help you make minor changes to your routine to get even more out of pruning.
McNaughton, Virginia. Lavender The Grower’s Guide. Portland: Timber Press, 2000. 3–6.