Q.Chinese chestnut trees
I have a 15 year old tree that produces thousands of pods with undeveloped nuts in them. Thinking it was a pollination problem I planted 2 more chestnut trees within 20 feet of the original tree. The young trees bloomed this year but the older tree is still loaded with undeveloped pods. Is there something else I should be doing? They are quite close to an apple and a pear tree. Does that affect the chestnut? Thank you.

Certified GKH Gardening Expert
It could be lacking in phosphorus or potassium, or even have too much nitrogen in the soil. Adding potassium, and phosphorus, as well as dolomitic lime for pH balance will help.
Alternatively, make sure what you have is what it is supposed to be. It is common to mistake a certain birch tree for for these, as they have similar pods.
Here is an article about the Chinese chestnut: https://www.gardeningknowhow.com/edible/nut-trees/chinese-chestnuts/chinese-chestnut-trees.htm