The river birch is a fast-growing shade tree, usually multi-stemmed, that is very popular in landscape use. It has the beautiful exfoliating bark that is the hallmark of many birches, but it is one of the most adaptable species, with better tolerance for poorly drained soils and warm conditions. The river birch has a rounded compact form and semi-arching branches. The white bark peels back to reveal salmon-red inner layers. The medium-to-dark green leaves are 1 to 3 inches long, oval-shaped with serrated edges, and are white on the underside.
The river birch is monoecious, bearing male and female flower clusters called catkins on the same tree. They form at different times; the male catkins form in fall and bloom in the spring, when the female catkins appear. After pollination, clusters of small, brown winged fruit form in the spring.
A river birch is an excellent choice as a specimen tree. The salmon-red peeling bark will provide color throughout all of the seasons. This tree works well in locations with wet soil, such as along ponds and streams or in low-lying spots. Dwarf varieties can be used in rain gardens or even as foundation plants.
Plant a river birch tree in spring or fall when the soil is moist and the temperatures are cool. This is a fast-growing tree that averages about 36 inches of growth per year. Dwarf varieties may grow a bit slower, taking 10 years or so to reach 10 feet. River birches are not particularly long-lived trees, however. While some native trees have been known to live 150 years, most of the cultivars are reaching the end of their expected lifespans within 30 to 40 years.
|Botanical Name||Betula nigra|
|Common Name||River birch, water birch, black bird, red birch|
|Plant Type||Deciduous tree|
|Mature Size||40–70 feet tall, 40–60 feet in spread; dwarf cultivars are also available|
|Sun Exposure||Full sun to part shade|
|Soil Type||Damp, consistently moist soil|
|Soil pH||5.0 to 6.5 (acidic)|
|Bloom Time||Spring (flowers are indistinct)|
|Flower Color||Brown, green|
|Hardiness Zones||4 to 9 (USDA)|
|Native Area||Swamplands, floodplains of Eastern U.S.|
River Birch Care
A river birch is well suited for growing in constantly damp soils where most trees fail to thrive. This tree is native to swamplands and floodplains surrounding rivers and bogs, and it will grow best in locations that are similar to that natural habitat. It likes a somewhat acidic soil, and may develop iron chlorosis and yellowing leaves if the soil pH is too high. If you grow it in as lawn tree, be prepared to water very frequently to give it the moisture it needs. If pruning is necessary, avoid doing it in spring when the sap is running.
A healthy river birch will be fairly trouble-free—one of the more dependable of all the birch species. When problems occur, it is usually because the tree has been planted in less-than-ideal circumstances.
Plant river birch trees in full sun to part shade locations.
Plant this tree in a location where the soil is shady, moist, and has good drainage. The soil should have a pH between 5.0 to 6.5 for best results. Iron chlorosis may affect the tree if it is not within this range. This tree does not care for alkaline soils, nor will it do well in soils that frequently dry out.
Water deeply for two to three hours once a week to keep the soil around the tree moist. This tree needs damp soil and will suffer during periods of drought. Adding mulch will help keep the soil cool, which will protect the roots from drying out. Do not place mulch where it will touch the trunk. A thirsty tree is more likely to suffer insect or disease problems.
Temperature and Humidity
These trees are suited to grow in USDA zones 4 to 9, but they prefer relatively cool climates. The species version will not perform well in the southern end of this range, but several cultivars are bred to do well in warmer climates. This tree prefers humid weather over dry climates.
Fertilizer is only needed if the tree shows signs of distress. Weakened trees will benefit from a spring feeding with a slow-release granular fertilizer mixed into the soil over the root zone. Where soil is too alkaline, feeding with an acidifying fertilizer may be useful.
River Birch Varieties
- Heritage is a commercially trademarked version of Betula nigra ‘Cully’. It has larger, glossy, dark green leaves, interior bark with a nearly pure white color, and is more heat tolerant than the species.
- 'Summer Cascade' (Betula nigra 'Summer Cascade') is a weeping form that grows only 6 feet high and 10 feet wide.
- Fox Valley is a commercially trademarked version of Betula nigra ‘Little King’. It is a compact tree growing 10 to 12 feet tall.
- 'Shiloh Splash' (Betula nigra 'Shiloh Splash') is a smaller cultivar, growing 10 feet high with an 8-foot spread. It has variegated foliage with creamy ivory edges.
River Birch vs. Paper Birch
River birch looks very similar to the paper birch (Betula papyrifera), but river birch has a better tolerance for warmer climates. Paper birch is hardy further north (to zone 2), and its surface bark is a purer white.
Pruning a River Birch Tree
River birch is best pruned after August 1. Avoid early spring pruning while the tree's sap is running. Late spring and early summer are when bronze birch borers are out in full force and may take advantage of fresh pruning wounds.
Leave at least 75 percent of the tree intact when pruning. Branches that rub together should be removed. Also remove branches that grow straight up from the trunk, as these have a weak attachment.
Propagating River Birch
Propagating trees is not a common DIY activity, since most people don't want to wait many years for the specimen to grow into a real tree. If you want to try it, though, river birch is a fairly easy tree to reproduce, either through collecting the seeds and planting them, or by taking stem cuttings and rooting them. Birch trees are fast-growing enough that you won't need to wait decades to see real results.
To propagate by seed, collect the fuzzy catkin-like fruits in May to June from the tips of the branches as they begin to change from green to brown. Separate the seeds from the catkins and store them in the refrigerator until you plant them. Plant them them in pots filled with potting soil and keep them in bright conditions (16 hours a day or more) until they germinate and sprout. Continue growing in pots until they are large enough to transplant into the landscape. If necessary, the potted saplings can be left outdoors over winter in a sheltered location, then planted the following spring.
To propagate through cuttings, in early spring as new growth is beginning take 6- to 8-inch long cuttings from new wood from near the tips of the stems, where new wood joins old wood. Make sure the cutting has several leaf nodes, then remove all but the top one or two leaves. Dip the cut end in rooting hormone, then plant the cutting in a sandy potting mix. Place the potted cutting in a bright outdoor location and keep the soil moist until new leaves begin to sprout. Continue to grow it in the pot until the tree is large enough to plant in the garden.
The failure rate for propagating from cuttings can be high, so it is best to take at least five cuttings to ensure that at least one develops roots and grows into a sapling.
Common Pests/ Diseases
- River birch is one of the more trouble-free of the birches, but like any birch, it may fall prey to the birch leafminer (Fenusa pusilla). The symptoms are large blotches on the leaves. The best treatment is a systemic pesticide that targets these insects. These chemicals are best applied by a professional.
- This tree is more resistant to the bronze birch borer (Agrilus anxius) than other birch species, but it is not immune. These beetles tunnel into the bark and feed on the cambium layer, disrupting the tree's ability to transfer water and nutrients. Symptoms include yellowing and thinning of the foliage, beginning with the upper crown. A systemic pesticide applied by a professional may defeat bronze birch borer if the damage is not yet widespread.
- Anthracnose leaf blight (Gloeosporium betularum) is a fungal disease that causes leaves to curl and wither after developing splotches or brown spots. The general recommendation is simply to keep the tree healthy and tolerate minor disease. Only in very severe cases is treatment with a fungicide recommended.
- Birch dieback is a fungal-related disease in which entire branches of the birch tree begin to die back. Damage from bronze birch borers can also initiate birch dieback. When you notice affected branches, prune them back to good living wood. Then, take measures to carefully nurture the overall health of the tree, making sure it gets plenty of water. Have the tree examined for bronze birch borers, and treat if necessary.