Yes, Osmocote plus is safe to use on trees on shrubs but a slow release plant food like Osmocote will not improve your soil so you may also want to add a compost mulch on top of the roots of your young trees. Do not let the mulch touch the bark of the trees but instead layer it on top of the soil in the area where the tree roots are spreading outward. Put down the fertilizer first, working it into the top few inches of soil, then cover this with a one inch layer of bark chips, compost or wood chips leaving the area next to the trunk open like a doughnut. The mulch on top of the soil will help to keep out weeds and seal in moisture as well as improve your poor soil. Keep growing, Marianne Binetti