Do you want to start a number of plants, or just move a plant or two from one spot to another?

Al

I want to start a number of plants

If you only want a handful of plants and you have more than 1 plant to work with, here's what I would do. Fertilize well, wait a week or so, and cut the plant back to somewhere between 3 & 4 in the image. The idea is to get rid of the blooms (a strong energy sink) and force it to back-bud so you can take woody cuttings in fall. Stick the cuttings in a fast-draining medium you can keep damp. Soggy or wet won't do. I don't know where you live, but you might be able to leave them outdoors all winter if the cultivar is hardy where you live. By spring, they should have rooted and can be planted out after they put on a bit of growth. Next year, you can take soft or summerwood cuttings and clone as many plants as you like.

If you only want a handful of plants and you have more than 1 plant to work with, you could prune the plant back to point 2, take the top off at 3, and treat the basket-shape of branches as a single cutting. You'll get roots along all of the branches just above where the stem makes the transition to multiple branches. In spring, each branch can be separated from the clump and potted up or planted out. A year in a pot before planting out would be better.

Al

many thanks. i live in Czech Republic which is in zone 6 i believe.

And i have many plants to work with.

In your 2nd suggestion, is there any risk to lose all plant if i cut it at point 2?

Yes. You risk losing the plant if you cut into old wood. 4 and 5 are flower stems so they're no use to you. 3 is getting dangerously close to old wood. Cut between 3 and 4.

3-4. Thanks a lot!

Technically, old wood is woody growth a plant puts on up until the point in time the vegetative terminal bud at branch ends is set in fall or winter at the end of the year's growth. New wood is growth that begins at the beginning of the subsequent growth period and includes all wood distal to the terminal vegetative bud scar. For the purpose of creating propagules, highly lignified new wood can be and is treated in the same manner as old wood.

I regularly grow woody material to hts of 8-10 feet (3M) before cutting it back only inches from ground level as the first step toward creating larger bonsai. All trees considered focal points of the images in the following 3 shots were 8-12ft (3-4M) tall when they were chopped and lifted (on the same day) from the ground. All trees, and many others like them, are well along on their journey toward becoming bonsai. I treat nearly all types of woody material in similar fashion, even if they are being groomed only as palm-size trees. There are a few trees and woody plants that shouldn't be cut back so hard there is no longer any foliage (but lavender is not one of them, mostly evergreens, like pines and junipers. Even then, the rule doesn't hold fast for the entire genus.

maple^^

Maple^^

L-R Chinese quince, hedge maple, bald cypress, American hornbeam

If the plant (lavender) is in the ground, there is almost no chance the plant (stump, if you will) will do anything other than back-bud profusely. There is a far greater chance the propagule (the part of the plant between points 2 and 3) will fail when treated as a cutting than the already rooted plant. If you still harbor concern that your plant won't survive if you cut it back into old wood, like the trees in the images have been, simply leave the first (lowest branch) attached to the trunk/stem when you take your propagule.

The plant could also be stooled. Just cut the bottom out of a nursery can, slip it over the plant, fill with soil up to half-way between line 2 and 3, cut the top of half-way between 3 and 4, and keep soil moist. When spring comes, all branches above the single trunk will have roots. You can strip a swath of bark off of the outside lowest part of each branch above the stem before you fill the pot with soil if you like, to help ensure faster root formation.

Lots of ways to skin that cat because lavender is easy to propagate. You can also ground layer by making a depression in the soil, pinning a branch in the depression, and covering the branch with soil. Separate the branch from the mother plant in spring.

Notice 2,3, & 4 in the sequence. At 4, instead of a mound, you would use a pot with most of the bottom cut out, slipped over the plant and filled with soil.

Al

I don't intend to pursue this much further other than to say that every source I've ever read, and personal experience, say that lavender is a plant which does not respond well to cutting back into old wood. It doesn't behave like many other woody plants so comparisons don't really work. In the ground, far from there being 'almost no chance' it is actually quite likely lavender will not back bud. Whether it is less likey to fail than a cutting isn't the issue. This is a messy website but these people grow lavender for a living - see what they say about cutting into old wood. https://everything-lavender.com/woody-lavender-plant.html