Answer: I don't think there's anything in the soil, except tree roots. Since the trees are large, they have the advantage when it comes to slurping up moisture and nutrients. Your new little annuals and perennials can't compete. The best defense is to water and fertilize more often, so both the trees and the plants have ample supplies. If all else fails, to stop the competition, you may have to resort to planting in above ground containers!
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