How to Fertilize River Birches

The river birch (Betula nigra), also known as red birch, water birch or black birch, grows natively in the Southeast United States to as far west as Texas and is found sparsely as far north as Minnesota. The river birch prefers wet, well-draining soils along riverbeds rather than clay. It is adaptable and grows in dry areas if adequate water is available during its establishment. Soil with a pH higher than 6.5 can result in iron deficiency and chlorosis. Fertilize river birch only if the soil is deficient in appropriate nutrients.

Things You'll Need

• 30-10-10 slow-release fertilizer
• Chelated iron tablets

Instructions

1. Conduct a soil test to determine the pH and nutrient levels currently available in the soil. River birch grows best in acidic soils with pH less than 6.5.

2. Apply the 30-10-10 slow-release fertilizer in early spring or late fall, but not August or September to avoid promoting new growth just before winter. Apply the fertilizer to the absorbing root area only once or twice a year as needed. The absorbing roots start several feet from the trunk and extend beyond the outer branches by another 40 to 50 percent.

3. Apply chelated iron if the river birch shows signs of chlorosis -- yellow to pale-green young leaves with green veins. The amount needed varies depending on the soil test and the manufacturer's instructions, but Dennis W. Carlson of the Kansas Forest Service recommends 1 lb. per inch of tree diameter measured at 4 feet above ground level. Drill or punch holes 6 to 10 inches deep and 2 feet apart over the absorbing root area. Start 2 to 3 feet away from the trunk and extend beyond the drip line. Lowering the soil's pH also allows the tree to utilize the iron available in the soil -- at a pH of 7.0 or higher, the iron is in an insoluble form that trees cannot use.

4. Water the river birch after fertilizing. A drip hose works well when extended around the tree's drip line upside-down and run for several hours until the soil is moist for a depth of 1-1/2 to 3 feet.

References

• U.S. Forest Service: Betula Nigra L., River Birch
• TreeHelp.com: Birch Tree Care
• Wilson Bros. Nursery.com: River Birch Feeding Instructions
• U.S. Forest Service; How to Grow and Maintain a Healthy Birch Tree; Steven Katovich; et al.
• Kansas State University; Iron Chlorosis in Trees; Dennis W. Carlson; September 2003