I used your formula for determining if my soil has good/poor/no drainage. I used a post hole digger to dig two 12" holes 10' apart. Opening at top 7", filled it with water, waited approximately 24 hours filled again. One opening drained in 28 minutes, the other 38 minutes. The ground has never been used before. Just hard dirt In Phoenix, AZ desert. Want to set out two muscadine (grape) plants. Do I need to do anything to the soil? Thank you very much. Frank
