Q.What can I do about the leaves of my young fruitless mulberry tree turning yellow with the edges turning brown?
It’s been very hot here in TX (109 today) but I’ve been watering the tree regularly. The leaves look scorched. No photo.
From your description and the extreme heat, it sounds like you are on the right track with stepping up the watering.
But How you water is important. Be sure to do a heavy soil drench throughout the absorbing root zone, all the area underneath the foliar canopy an a little beyond. Don't just sprinkle a little, flood irrigate. Don't water only near the tree trunk, but set up a sprinkler or soaker hose or just lay a running hose end out for awhile and then move it around. Try to achieve at least six inches of water penetration into the soil profile, 10 to 12 inches is even better. A layer of mulch helps to retain soil moisture.
