I live in Southern New Mexico. Mulberry trees are prevalent here. Mine is in the middle of my yard, well over 40 years old, and has been producing smaller and less leaves for the last few seasons. This season, much less leaves. The tree has been trimmed and maintained well. What is going on with it?
Fruitless Mulberry Tree Health
Certified GKH Gardening Expert
The declining leaf growth is an indicator of an unhealthy tree and it may be do to lack of water, lack of proper fertilizing, Sooty Mold, salts from desert run off, or improper pruning.
Fruitless Mulberry are classified as heavy water required. During hot weather the tree will need to be watered 2 to 3 feet deep every 5 to 7 days.
The sandier the soil, the more water it will need.
Irrigation should extent out to the tree canopy drip line.
Long term water stress can lead to the decline and even death of the tree.
Mulberry Trees need fertilizing 2 to 3 times a year with a nitrogen fertilizer.
Lack of nitrogen results in less leaves, yellowing leaves and poor growth.
A stressed tree is open to diseases.
Accumulation of salts that are naturally occurring from desert sands can also build up in the tree. Deep irrigation helps dissipate the salt.
Here are some articles with more information.