How hard should you prune lavender after it has finished flowering?
Lavenders benefit from annual pruning immediately after flowering to help them remain compact, dense and shapely. If you prefer to let them run riot, au naturel, they will become sprawling and woody and can sometimes take on a beautiful gnarled character but then it will be too late to change your mind as they cannot regenerate when pruned back into thick old wood. Learning just how far you can cut back lavender and have it rejuvenate is a matter of trial and error, but younger plants can definitely be cut back harder than older ones.
To test the limits, after my lavender finished flowering this August, I decided to do an experiment and prune them back much harder than usual. I had read an article saying that most people assume lavender cannot regenerate from old wood, so only give their shrubs a light pruning. Harder pruning, they explained, was not only possible, but desirable, as it would lead to more compact, dense and robust plants. So I decided to give it a go. Here is what happened…
The photo at the top of this post shows my white English Lavender flowering it’s heart out in the middle of July. The last flowers go over in the third week of August, when I usually take the secateurs to them and cut back into green wood, not too far, leaving the clumps like this…
They soon recover, but with such a light prune the plants increase in width by about 4 inches per year. If I carried on like this they would soon outgrow their space. In the past I had assumed that they would not tolerate heavier pruning so I had lived with this gradual bloat, but they are now approaching the limit of their space and I need to keep them under control, or remove them altogether. This set me wondering: have been over-cautious? Perhaps they can take a heavier pruning than I have given them credit for.
There is a clue, if you look closely at the stems, you can see how far back the buds go. If you cut back harder, these lower, smaller buds should grow away fine. But would there be enough to create a dense new mound of foliage? Only one way to find out…
After looking carefully for these tiny lower buds I took the secateurs to the lavenders for a second time, taking off another 2 to 3 inches of older wood. It was a bit disconcerting to see the first shrub I attacked left with almost no leaves!
The lavender in the background has only had the first light prune. The one in the foreground has had the second, much harder pruning. After completing the pruning of all four of my lavenders I mulched and watered them to help them recover.
Two weeks later in late August… The tiny buds are beginning to break. There don’t seem to be many on each stem. Did I cut back too far?
The plants are now covered in new foliage which seems to have broader leaves than usual. Although some of the heavily-pruned stems have died back and have no new shoots, there is new growth emerging deep down in the centre of the shrub coming from close to the base which I did not expect. I now think I should have been brutal with these plants from the start.
A close look reveals lots of new growth coming from the base and centre of the plants. I now wonder whether I could have cut back even harder in August, especially as these are relatively young plants. The dead stems that have not produced shoots now look unsightly and could, no doubt, be pruned out, but I will leave them until spring to help protect the new growth from the frost.
Here are the other two lavenders which are beginning to fill out reasonably well. I wonder what they will look like by the spring? Hopefully dense rounded mounds, in keeping with the other shrubs in this bed. We will have to wait and see.
[I’ll post further updates below as time goes by]
[Edit: May 2020]
The following spring
9 month’s after hard pruning
As you can see the lavenders have not only recovered from their heavy pruning, but have come back fully, producing a dense bun of foliage with plenty of flower spikes.
Update May 2021
The secret to keeping lavenders compact and domed is to prune low every year to prevent the woody base from expanding. The maintenance from here on will be to cut back to approximately the same height every year, i.e. close to the hard-prune point above.