Loving moist and acidic soils, the river birch (Betula nigra) is a heat and drought-tolerant tree native to eastern North America. Its tan, exfoliating bark is a key ornamental feature, as is the glossy green foliage that turns yellow in autumn's chill. Lots of sunshine, moist to wet soils and fertile, non-alkaline ground and a cool-season dormancy is key to getting a river birch to prosper and look its finest.
Ideal Growing Conditions
Provide 1 to 3 inches of water per 7 to 14 days to the root zone of a river birch in the growing season. Natural rainfall, an automated irrigation system or a portable sprinkler from a garden hose can supply this moisture. This regimen is particularly important when you are experiencing a drought in your region.
Remove competing shrub and tall trees if you feel they are physically encroaching upon the river birch or are shading the tree so much that the canopy is sparse or lopsided as it grows to reach light. The birch should receive at least 4 hours of direct sunlight each day, ideally a minimum of eight hours for best growth. In hot summer climates, however, shade in the hottest part of the summer afternoon is recommended.
Test the pH of your soil with a kit from a garden center or submitting a soil sample for analysis at your local Cooperative Extension office. Acidic soils, those with a pH reading less than 6.5, are best, and if you need to lower the soil pH, the office can provide guidance for cost-effective methods.
Place organic matter around the base of the tree to a depth of 2 to 5 inches, keeping the mulch layer 3 to 5 inches away from the trunk(s). The mulch slowly decomposes, releasing nutrients into the soil for the tree to absorb. Good acid-forming mulches include decomposed oak leaf mold, pine straw, pine bark or compost.
Replenish the mulch as needed, sometimes as much as twice or thrice a year depending on climate and the rate at which the mulch decomposes and compresses to a layer less than 2 inches in thickness. Allow autumn leaf litter to remain on the ground under the tree, too.
Consider casting a well-balanced, slow-release granular fertilizer under the branches of the tree in early spring if more robust or healthier new growth is desired that growing season. Follow product label directions for dosage recommendations.
Sprinkle Epsom salt granules under the tree twice a year in sandy soils, especially those neutral to alkaline in pH (pH 6.5 or higher). Evenly broadcast 1 to 3 cups of the crystals on the soil in a radius-ring of 5 to 8 feet around the tree trunk(s). Epsom salt provides magnesium, a micronutrient especially difficult to absorb by trees in non-acidic soils.
Remove dead, diseased or wounded branches any time of year when seen. A visual examination of the tree's branches and overall structure is best done twice a year when the leaves are absent: once in spring and again in late autumn. Branches that rub against each other or cross through the upright structure of the tree require removal as well.
Make pruning cuts with a hand pruners or loppers 1/4 inch above a living branch junction, dormant bud or leaf. Branches needing removal that are larger than 1 inch in diameter should be pruned with a hand-held pruning saw.
Support long or heavier branches with your spare hand as you saw or cut them away. This avoids a situation when the weight of the branche causes premature breaking and tearing of the bark when the pruning cut is nearly through the wood.
Allow pruning cut wounds to bleed and then callus and dry on their own. Do not paint or seal wounds on the tree. Bronze birch borer is not a problem with river birch, so permit the tree to heal and compartmentalize its pruning wounds naturally.