Dear Judy,
Sorry you have been having trouble. Lavender is truly a useful and atractive plant. Would you be so kind as to tell us: 1)What variety of lavender you have been planting (some, like "Spanish" and "French" are not cold hardy past zone 8) and 2) what time of year have the plants been dying off - summer or winter? Then, I believe we will be better able to help you with your question.
Sincerley,
Matt Di Clemente, Brick, New Jersey