Sorry. I meant -English- lavender. I have -english- lavender. I was reading an article on shaping french lavender and typed the wrong title. Can't see any way to -edit- a post after hitting submit.

---JC

Shear back in early spring. Stay out of old, bare woody lower stems, these do not re-sprout well. If shearing newer parts only does not make as dense as wanted, remove and replace with younger specimens.

Layering is a great way to start new plants to replace older ones.

I'm wondering what kind of lavender gets 4 to 5 feet tall?

Lavandula x alardii. Not a hardy English type but it is said to grow that tall.

I'm not sure I understand what it is you are trying to do. English lavender naturally grows into a mound or 'globe' shape - are you trying to develop a different shape? This is not a plant that would lend itself to topiaries or shaping very easily. A hedge would be a simpler approach but again, more of a rounded, mounded look than a precisely sheared block. Since lavender tends not to be a very long lived plant, I'd wonder at the advisibility of its use as a hedge plant.

It is recommended to prune lavender twice a year - once in the fall lightly, removing old flower stems and just an inch or two of foliage. In spring as the new growth develops, you should cut back more severely but as bboy notes, not into any bare woody stems. This twice annual grooming will help to encourage a dense, compact plant with additional flowering stems. It is important to start this practice early in the life of the plant - allowing even a young plant to become leggy or splay open is not a recoverable situation.

Open your favorite search engine.
As the search phrase, use "lavender hedge" (without the quotes).
Then hit the Enter key. Tada! Lots of info.

Do you know what variety you have? It might make a difference as to how tall they will grow.

I had Lavandula angustifolia "Munstead" which did well in zone 4, semi-arid 8250' above sea level. "Well" as in one lived, one died. The one that lived had the better drainage site and less tiny dogs wanting to pee there. Munstead is apparently one of the varieties recommended for hedges, or so my small amount of internet research has revealed.

If your's grows out to the side with pruning, consider looking at where the cuts will be made. If the node you are cutting above is located on the outside of the plant, it might grow out. If it is located more to the center of the plant, maybe it will find its way upwards.

I hope you are able to make it work.