The Life Span of the River Birch

The notably trouble-free river birch (Betula nigra), native to the Eastern United States and prized for its colorful bark, grows from 60 to 80 tall with a canopy spreading up to 50 feet wide. Under ideal conditions it lives from 50 to 75 years. Growing a river birch in conditions similar to its natural growing environment and ensuring that it is adequately watered are key to keeping it healthy and extending its longevity.

The river birch will grow in U.S. Department of Agriculture plant hardiness zones 5 through 9. With a soil and climate that encourages longevity, the fast-growing river birch adds from 13 to 24 inches per year until it tops out at maturity.

The bark of the river birch sheds heavily in patches, displaying an attractive trunk of gray, lavender and orange. This is natural and part of their attraction. Other birches typically have gray or white bark. River birches also readily shed dead branches and twigs, but this does not affect their longevity.

River birches are native to alluvial soil, the rich soil deposited by rivers and associated with deltas. It is found on stream bottoms and growing along river banks. These trees have a high tolerance for acidic soils, associated with moist climates. They don't mind soils that are periodically wet.

USDA zones are based on average winter low temperatures; they only indicate how much winter cold the river birch can withstand. USDA zones do no address summer heat which increases water loss, stressing river birches and affecting their longevity. If you have hot summers, you need access to water necessary to keep the soil moist.

Water a river birch weekly during the spring and summer growing season when rain is lacking, wateringabout 18 inches deep over a two- to three-hour period. If you can form a ball of soil with your hand, the soil has had enough water. If the soil crumbles, it needs more water. Decrease the water in late summer so the tree can begin preparing for winter.

Lay a 2- to 4-inch layer of mulch composed of wood chips, leaf compost or shredded bark from the base of the tree and out past the canopy, to hold in soil moisture -- but don't allow mulch to touch the trunk. Avoid placing plastic under the mulch.

Do not add fertilizer unless you have the soil tested to see if it lacks nutrients. You can buy a soil test kit at a garden supply center. Test the soil every three to five years.

If you have grass under the tree, scatter 1 2/3 ounces of nitrogen in a water-soluble, granular fertilizer on the ground around the tree in a circle with a radius of 12 1/2 feet from the center of the tree. Water well. To calculate nitrogen in a fertilizer, remember that the numbers on the package give the percentage by weight, of nitrogen, phosphorus and potassium (N-P-K). Apply once in the spring and once in early autumn before the tree goes dormant.

In soils with a pH above 6.5, associated with dry areas, river birch may develop chlorosis, the term used to describe leaves that turn yellow between their veins. Chlorosis is usually caused by soils with a high pH that prevent a river birch from absorbing minerals, including zinc, manganese or iron. River birches with chlorosis typically suffer from a lack of iron.

Growers can address chlorosis in river birches by using sulfur to lower the soil pH, but rapid lowering of pH can damage the tree’s health. Adding sulfur to lower soil pH is complicated, but roughly 1 pound of elemental sulfur per 100 square feet tilled 6 inches deep will lower 7.0 pH soil to 6.5. Add 50 percent more sulfur for clay soils.

Arborists discourage using nitrate fertilizers on a river birch suffering from chlorosis.

The river birch is one of the most disease free of birch species, having few problems with disease or insects. The insects that do affect it do minor damage, with the exception of the bronze birch borer, which infests and kills birch trees weakened by poor soil nutrition or lack of water. The river birch resists the birch borer better than other birch species, but is still susceptible. There is no effective treatment. Trees should be chipped or burned to destroy the larva and keep the insect from spreading to other trees.

The birch borer infests tree wounds, so pruning should be done in late summer or autumn, not in late winter or early spring when it oozes sap from wounds.