My only knowledge is what I read, so take it with a very large pinch of salt.
I keep reading "crown rot" which sugegsts it is surface damp that is the big risk.
I dunno, "heavy clay soil plus lots of rain" spells drowned roots to me!
>> in low lying spots I build a small mound as well. Just 6"H x around 2'W.
Agreed: before I plant anything, I create a drainage trench below grade and a raised bed above grade. That is relatively easy compared to creating the soil! I screen the clay and then add 1-2 partws of amengments to 1 part of clay, adding both organics (compost & aged manure) and driange coarse stuff like pine bark and very coarse sand / crsuhed rock.
>> I also stay away from organic mulches as that holds too much moisture around the crown.
That sounds smart, and yet, here int he summer, it is so dry that mulch is necessary. I might use small pebbles around the crowns when i get around to a raised bed for lavender.
One appeal of growing in pots is that I can put a pot anywhere there's sun, and I only need a few gallons of potting soil instead of cubic feet of amended clay plus trench plus raised bed.
