River birch trees are prized for their unique trunk bark and airy canopies. While not considered troublesome trees, some basic cultural requirements must be met in order for river birch to thrive. Equally important is to keep the tree healthy and avoid becoming susceptible to any of the internal or environmental weaknesses common to their species.
Sensitivity to Alkaline Soil & Chlorosis
River birch trees cannot tolerate alkaline soils with higher than a 6.5 soil pH and grow best in slightly acidic soils (pH between 5.0 - 6.0). In alkaline soils the leaves of river birch experience chlorosis and turn yellow. Heavy amounts of phosphorous in the soil and in applied fertilizers can exacerbate this problem by blocking the uptake of iron. Acidifying soil amendments and low-phosphorus complete fertilizers can correct the imbalance if the practices are maintained over time.
Susceptibility to Birch Leafminer
Birch leafminer is an insect that, while not life-threatening to the tree, can destroy its beauty. The leafminer sucks the phloem out of the leaves, leaving them brown and desiccated and also causing defoliation. It can also weaken the tree creating the pre-conditions for and susceptibility to the more deadly bronze birch borer.
River birch trees demand frequent slow, deep watering to maintain very moist to nearly wet soil at all times. An average requirement would be 2- 3 hours of slow flowing water to wet the soil to a depth of 8-18 inches once per week every week from spring through August. The only exception would be when natural rainfall has been significant.
Susceptibiity to Bronze Birch Borer
Bronze birch borer is a beetle that attacks compromised birch trees eating canopy foliage and boring into woody tissue of the tree. Defoliation at the very top of the tree is the first sign of a serious infestation. Over a a unusually dry season or longer over a year to even three years a tree can be killed by the activity of successive generations of the beetles. Once significant defoliation has occurred in over half of the canopy, saving the tree is very difficult if not impossible.