I built a mound of earth with sand and soil. Then, after the ground is frozen, around mid-November, I am going to cover the lavender plants with a heavy floating row cover for protection over winter.
Lavenders do not like their roots wet and they do not like to be fertilized. They do like lots of sunshine with no watering. They like a pH of around 6, but not too acidic. Finicky!
Quote from Moore Manor Lavender:
If you plan on growing lavender in Maine, for best results you should cover them once consistent cold occurs. Don’t be in a rush or the mice will make their home along with the protected lavender and ruin a lot of it. Wait until the mice have made their winter burrows elsewhere. Cover with a thick layer of straw, or heavy floating row cover that’s pinned or weighted down. It should be checked periodically to make sure the wind hasn’t uncovered any of it.Once the weather has warmed, and there’s no threat of a hard freeze the covering can come off. Don’t be distraught if it looks as though the lavender is dead. It takes a bit of warm weather and sunshine for the lavender to start its new growth. By May you should see the your lavender coming to life.