I want to plant blackberries, raspberries, and a vegetable garden in the heavy clay soil in my backyard. So, I plan to heavily amend it by spreading 3" expanded shale and 6" of compost and working that 12" or more down by double digging.
Since I don't know this soil's history, I think a soil test is a good idea so I can learn what other deficiencies I need to correct via fertilizer or pH adjustments. Should I send in soil samples before or after I amend the soil? And if after, how long do I need to wait after mixing all the soil up?
I don't think it matters for this question, but I live in a suburban house around Dallas. Zone 8a.