I live in zone 8-10, SLO California, I planted lavender all on 3'x10' mound around my 18x18 u shaped patio. I have on bush of beautiful purple flowerings, the lavender bush grew to 5'x3' HUGE, next to this lavender I have planted three more 5gallon lavender plants but they keep dieing, there is a 3 foot space between plants.
Hi, Well there's no clear answer to your problem, but my hunch is that the locations where your lavenders are dying has a soil problem. Lavender is very sensitive to poorly drained soil. Check the drainage of the problem sites. Poor water on the location and see how long it takes for it to disappear. If it takes more than an hour to drain, you may have a problem. Generally, lavender's three problems are lack of drainage, not enough sun, or too cold of a winter. Since you are in central CA, I'm sure the winters aren't the problem.