How can I find out how to care for a plum, pear, and cherry tree. climate is cold winters and hot summers?

Question:The trees are all next to each other. The pears are small and fall off the tree with black spots all over (the leaves have the same black spots). The cherry tree only gives like 5 cherries. The plums fall off purple and small.

Answers:
sounds to me like they are too close together and using up all the nutrients from the soil

They do sell fruit tree nutrient spikes you can pound into the ground which may help