The river birch (Betula nigra) is a fast-growing deciduous 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 birch species, with better tolerance for poorly drained soils and warm conditions than most species of birch. Native to the swamplands and floodplains of the eastern United States, 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. River birch is a monoecious tree, containing both male and female flowers on the same trees. The male flowers are brown, drooping catkins, while female catkins are smaller and upright. The catkins add ornamental appeal to the tree's appearance in winter.
River birch is usually planted in spring or fall as a container-grown or balled-and-burlap plant, 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.
|Common Name||River birch, water birch, black bird, red birch|
|Botanical Name||Betula nigra|
|Mature Size||40–70 ft. tall, 40–60 ft. wide|
|Sun Exposure||Full, partial|
|Hardiness Zones||4–9 (USDA)|
|Native Area||North America|
River Birch Care
River birch is well suited for growing in constantly damp soils where most trees fail to thrive. Like most birches, it prefers an area where the soil is naturally cool. This tree grows best in locations that are similar to its natural habitat of swamplands and floodplains surrounding rivers and bogs, but river birch is a surprisingly adaptable tree that will also tolerate a dryer environment. It likes somewhat acidic soil, and may develop iron chlorosis and yellowing leaves if the soil pH is too high. If you grow it as lawn tree, be prepared to water it very frequently to give it the moisture it needs.
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 (at least six hours of direct sunlight on most days) to part shade locations.
This tree is best planted in a location where the soil is consistently moist—or where it can be watered frequently. The soil should have a pH between 5.0 to 6.5 for best results. Iron chlorosis may affect the tree and cause yellowing leaves 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. It has good tolerance for dense, poor-draining soils.
Unless the tree is growing in naturally soggy soil, it should be watered deeply for two to three hours once a week to keep the soil around the tree moist. This means a good soaking of 2 inches or more. This tree needs damp soil and will suffer during periods of drought. A thirsty tree is more likely to suffer insect or disease problems. . 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.
Temperature and Humidity
This tree is suited to grow in USDA zones 4 to 9, and has a better tolerance for warm conditions than most birch species, which decidedly favor cooler climates. Still, river birch performs better in regions without blistering summers, and warm climates may see its lifespan somewhat shortened. It is most prevalent in the humid regions of the eastern U.S., where it is often found in flood plains and swampy areas. 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. For the amount to use, follow the product label instructions.
Types of River Birch
There are several good named cultivars of river birch, each offering some improvements over the native species:
- 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.
- Dura Heat® (‘BNMTF’) is a more heat and drought-tolerant variety, with a dense, pyramidal growth pattern. The exfoliating bark is pinkish-orange in color.
River birch is best pruned in fall and winter. 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 through cuttings:
- In early spring as new growth is beginning, use sharp pruners to take 6- to 8-inch long cuttings from new wood 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 about 3 inches deep in a pot filled with 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.
How to Grow River Birch From Seed
The best way to propagate by seed is to collect some of the catkins from the tree in early spring; these are leftover catkins from the previous year, now fully dried and ripened. Plant 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. They can also be planted directly in garden soil in the locations you choose. These trees readily self-seed, and it's also an easy matter to transplant the young volunteers.
River birch generally overwinters without incident when planted within its established hardiness range. However, these are thin-barked trees that can be susceptible to gnawing from rabbits and other animals. Young trees will especially appreciate having their trunks shielded with hardware cloth or another tree guard for the winter months when hungry creatures are looking to gnaw.
Common Pests and Plant 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 diseases. 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.
Overall, however, river birch is one of the more trouble-free of all birch species, and is a good choice when other birch trees have proved to be problematic. Occasional issues with aphids or fungal leaf-spot diseases may occur, but they are rarely serious.
How to Get River Birch to Bloom
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. Although not particularly colorful, the dangling catkins do offer some winter interest, so it can be disappointing if the tree does not produce them.
River birches will take two or three years before they begin to produce catkins. Failure to bloom is usually traced to a temporary cultural problem—untimely frost that kills the buds as they are just forming, or prolonged drought. The tree almost always returns to a normal cycle when environmental conditions stabilize.
Common Problems With River Birch
In the case of river birch, yellowing leaves is usually a symptom of iron chlorosis, a condition in which soil that is too alkaline prevents the tree from absorbing nutrients properly. Soil amendments, or fertilizing with an acidifying fertilizer, may rectify this.
Leaves Are Puckered, Distorted
This is often a symptom of an aphid attack. River birch is particularly prone to spiny witch hazel gall aphids, but they usually don't require any treatment, as natural predators soon arrive to handle them.
Large Tree Is Dying Back
If you are seeing a large, formerly healthy river birch begin to decline when no environmental changes are evident, it is entirely possible that you are witnessing natural behavior—the tree may be reaching the end of its life expectancy. These are not terribly long-lived trees and it may be time to remove your tree and replace it with another.
Fungal leaf spot disease occasionally causes a river birch to drop its leaves—a problem that may occur in particularly wet springs. But this is not a fatal problem; the tree will easily recover.
How is this tree best used in the landscape?
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.
How long does river birch live?
River birches are not particularly long-lived trees. While some native trees have been known to live 150 years, most name cultivars have a lifespan of no more than 50 to 75 years.
What is the difference between river birch and 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.
River Birch Betula Nigra. Wisconsin Horticulture Division of Extension
Betula Nigra. Missouri Botanical Garden
River Birch. Clemson Cooperative Extension.
Plant Propagation by Stem Cuttings. North Carolina State Extension
Dirr, Michael. Manual of Woody Landscape Plants. Stipe Publishing, 1998
River Birch. Clemson Cooperative Extension.
River Birch. Ohio Department of Natural Resources
River Birch, Betula Nigra. Wisconsin Horticulture Division of Extension.