@Barkslip , I always wondered, how is this tree doing? Is it on the same clay? Did it grow?
I also have very thick, clumpy, clay soil in many spots. Maybe not advice for your situation and it’s probably not as effective as mounding, but per topic, this is what I try to do:
- Plant shallow, with root flares at surface level. Sometimes I plant quite higher than what the nursery had planted to the point where I have to trim off some smaller roots that grew from the trunk above the root flare.
- Make exploratory pokes with the shovel around a general planting site and choose the best spot with the best soil. Even in a small area, not all potential planting spots are identical.
- Take notice when it rains hard, and walk around. Note the areas that get super soggy and don’t plant there. Plant where it drains the best. You can always plant a Sweetbay Magnolia in a soggy spot. It would at least help pollinators.
- Try different rootstocks / type of plants. Don’t plant the same exact rootstock+cultivar in the same location. Einstein purported said “The definition of insanity is doing the same thing over and over and expecting different results.”