I wouldn't try putting them in the ground now. It's too late in the season for them to establish themselves and they wouldn't survive the winter. I would leave them in their containers until spring, then transplant them. Cover the plants with mulch then with some plastic and move the containers to a relatively sheltered area. My lavender is in fairly dry, sandy soil and seems to like it. Good luck!

I agree with mjw15618, I've always had lavender in my gardens, I love it. I would not try to transplant it into the garden now tho, it can be a bit finicky.

Thanks for the replies and excuse my ignorance but when I mulch and cover them with plastic do I cover the whole pots with plastic or just to the mulch? I could put them in my basement (minimal light but good shelter). Do I water them through the winter?

If you have several containers why not plant one in the ground & see how it does this winter?
I have some in a big cement planter - it has been growing for 2 years or more. (very slow grower...I started from seeds)
I don't do anything special to it.
I also have one that I bought, it is in a small plastic pot that I never got around to planting in the ground, it has survived several winters outside, no special care...

Depending on how much plastic you have, you can do either. Once the plants go dormant, you can move them into your garage. They won't need watered over the winter, but you can give them some if you remember to. I've overwintered mums and other perenials in my garage like this and have never had any problems. Come spring, uncover them and move them outside and give them a good watering. They should start coming back within a few weeks. Once they look green and healthy again, you can transplant them into your garden.

i beg to differ about keeping lavender in pots over the winter unless you have a frost-free place to keep them. soil in pots freezes faster than the ground leaving the plants more vulnerable.

the really critical factor in keeping lavender through the winter is impeccable drainage. if you have a slope or retaining wall, the top of that in full sun is ideal. also, DO NOT mulch right up to the stem; this promotes rot. if you use anything under the plant, make it grit or gravel.
they don't like permanent wet at all.

the cultivar or variety has something to do with hardiness, too. i'm in nj, a 1/2 zone colder than you, but i have 'hidcote' lavender plants (in the ground) that are upwards of 15 years old.

check hardiness ratings of yours. and good luck.

I would not keep them in containers outside for the winter, I should have added that. I would move them in to the garage or basement and allow them to go dormant for the winter.

I have Munstead lavender plants. I found the above info. very helpful. I will mulch just to the stem and then cover with plastic, put into the garage. One of the plants is in a large andeluze pot, very sturdy and that will probably go into the garage and the other is in a small pot that I could bring into the house.
That said, would it be a good idea to bring both into the house? I could do that.
Can you describe how and when I prune/cut back the entire plant when the blooms are spent.