Hello,

Thank you for contacting Ask Extension. It is great that you started with a soil test, but you should wait until fall to fertilize between the first and last frosts. Trees struggle through the summer months because of the heat and low amounts of water, so to add fertilizer into that scenario, you are forcing the tree to grow, which does not help the tree. The other time you can fertilize is late April to early May, but you have missed that window. 
I am not sure what size the trees are, but if they are large, and you are fertilizing your lawn, the trees indirectly are getting some of the nutrients at that time. 

I have included several publications for your reference:

Fertilizing Shade Trees | MU Extension (missouri.edu)

Fertilizing Trees and Shrubs and Nutrient Deficiency Symptoms | University of Maryland Extension (umd.edu)

https://www.canr.msu.edu/uploads/files/Nutrition_and_fertilization_BertCreggfinal.pdf