Answer: As a rule of thumb, a spot with bad drainage will have standing water after it rains, or will have particularly muddy, soggy, sloppy, soil compared to other locations in your yard. Often a low spot is poorly drained but a slope will be well drained.
You could fertilize the trees with a balanced all purpose granular fertilizer according to the directions on the label. However, the best way to know how much to fertilize them (and with what) is to run some basic soil tests and find out what kind of condition your soil is in to begin with. Your County Extension should be able to help you with the tests and interpreting the results.
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