You will need: Hedge trimmer, shears, or secateurs, and a cane or stick with a mark 8 or 9 inches from one end.
This trimming should be done in late August, when the final flush of flowers has died down. September is also fine, but it's best not to leave it later, or you will get sparser flowers next year.
Read more about growing lavender here.
It's that time, the end of August, and the lavender, which has flowered all summer, really, is coming to the end of its flowering season. And this is the time when gardeners have to be brave and take your heart and your secateurs in both hands, and start hacking. Let me show you why.
The reason we're going to be brave with our secateurs is because, as a negligent gardener, I let my lavender run to seed, and it's too late to cut it back and get it to flower again. If I'd cut it (deadheaded it) at the end of June, it would be in full flower again now. The reason we cut back hard is that, if I open up this plant and show you, is these little green growths down at the bottom of the plant, which are trying to get to the daylight. So, what we're going to do is take the top, the sides off the plant now, and I will show you the rule of three eights.
The rule of three eights is in the eighth month, that's August, which is where we are. We're going to reduce the height of your lavender hedge to eight inches, and you're going to reduce its width to eight inches. Marked off, say, on a cane so you can see more clearly what follows.
You see the mark, hopefully clearly, and you put the cane down to soil level, just in a touch, so the mark is roughly eight inches above ground level. I'm going to cut a slot through the top of the edge. I'm doing this with secateurs, normally you would use hedge trimmers, or shears. That's sort at the eight-inch mark. And then, I move the cane down the hedge a bit and I stick it into the ground as before.
And I'm going to do exactly the same again, and cut the slot. So now I've got two slots in the hedge; there's one. And if I come up the hedge, here's another one. Join those two together, so the whole of this section will be at eight inches tall. I'm not going to fill the whole thing because it'll bore you, but I'm keeping my eye on the slot that I'm aiming towards as I cut, so that even though this may not be absolutely precise, I'm going to join them up.
I've trimmed my little section. You can see a raggedy bit at one end, a raggedy bit at the other end. In real life, you're going to have to do this for the whole hedge.
So, the next bit is to take it back down to eight inches wide.
I've got my trusty measuring stick, and, this is a bit of judgment, really, hedges grow roughly evenly on either side, so I'm going to kind of trim to the edge of the stick. I'm going to do the same thing: cut a slot at one end, but this time being down. And then I'm going to go to the other end, and I'm going to cut a slot there. And if I'm doing a whole hedge, by the way, these slots, if you use the technique, cut sort of about one every meter, something like that, it's quite easy to join up.
This is seen from above. I've cut a slot here, where my finger is. In there, you can see that the hedge has gone in. I've cut one slot there and then I've cut another one here, and I'm now going to cut along the edge of the hedge like that on one side, and then on the other side I'm going to do the same thing, join them up. I should have something that's roughly square in shape, cross-section, eight inches high and eight inches wide.
There's the raggedy hedge, and you see this nicely clipped little bit, it's only about thirty centimetres long, just for the video, and then it goes raggedy again.
So you can see that the top's been taken off, and that the sides've been taken off on both sides.
The reason that we do this, as explained at the outset, is when you cut down the side of the hedge like that down here, these little growths, you can see little green growths, there's one there.
Those suddenly see the light. This year, they're going to put an appreciable amount of growth. You can easily see, oh, two or three inches. They're going to harden off. As winter comes, if there's a frost, they'll get through the frost, and they're going to be full of flower buds in a nice tight, tight bush for next spring.