River Birch Has Lost 25% of Canopy
I have a 20' river birch that was transplanted to our yard from a nursery 4 years ago. It has gotten less and less "leafy" every year - all at the top. This year the top 25% of the tree is leafless. We've had a lot of rain this spring. The bottom 75% looks great. What's going on? Feeding? We've done none. The soil is about 12" of topsoil then kind of sandy.
River birch prefer moist acid soil. I often see specimens showing signs of decline in their older years, especially on alkaline (high pH) soils. Pale green or yellow leaves with dark green veins is a symptom of a nutrient deficiency caused by high pH soils.
Start by improving the growing conditions around your birch tree. Remove any grass, stone mulch, or weed barrier under the tree. Replace it with a 2 inch layer of woodchips or perennial groundcover. Continue to water thoroughly often enough to keep the soil moist but not wet.
Apply Milorganite fertilizer in the spring before growth begins. This low nitrogen, slow release fertilizer contains iron and can help your plant without the risk of damaging your already stressed tree.
Check the trunk for injuries or canker (sunken or discolored areas) that might be interfering with the flow or water and nutrients between the roots and branch tips. This could be causing the top dieback you observed. If damage is found or the top dieback continues, consult a certified arborist for help with diagnosis and treatment. Check out the International Society of Arboriculture website www.treesaregood.com for a list of certified arborist in your area.