I would appreciate your advice on growing lavender in zone 6/7 in SW VA.

how deep do my raised beds need to be for english lavender like "grosso" or "provence"?

same question as above for french lavender "silver anouk"

I'm planting the lavender primarily to attract butterflies and want to get the most lavender in each of my raised beds. Thus, my plan is to plant the lavender about 1 1/2 feet apart in the raised beds and NOT GO FOR THE NEAT ROWS. Any advice on this?

BTW, After removing about 10 inches of red clay from each bed, I put down about 2 inches of gravel and added about 8 inches of loamy soil( 1/3 top soil, 1/3 porous sand, 1/3 compacted manure) to each raised bed. My research indicates that I should NOT USE my regular tree bark mulch but should mulch with porous sand. Any reactions to my preparations/plans?

Thanks,

mike