1. Excavate the top 4-6 ins layer of dirt and fill back up with new topsoil of good quality.# v; J$ x% s" x1 ]8 E; w7 S
2. Reduce the use of chemical fertilizer and use organic one instead.
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I should tell a bobcat is required if you wanna do the whole front/back yard OR just spot-excavation (dig a bigger and deeper than normal hole, dump the old dirt and back fill w/ good topsoil when you want to plant a new tree) if you gonna do the job yourself.