I’m watching this because I have the same questions…I have a nice Lavender plant on my deck and I tried to mix sand into the potting soil to help it drain and prevent rot but I don’t know if it made it through winter yet.
I have seeds for Lavender and your question may provide experience I don’t have. Thanks!
The Dirty Fucking Hippies Were Right!
We do what we can, what we must and we hope for the best while expecting nothing.~ Me
One thing I found that helped was making my own potting soil. Lavender prefers alkaline soil, and most potting mixes use peat, which increases the acidity. It also needs good drainage. Last year, I got about 75% germination using a mix of vermiculite and coconut coir, which provided both the drainage and the alkalinity. I believe they sprouted in a few weeks, and they were all nice little plants by the end of the summer.