A fast growing large tree with beautiful creamy, peeling bark that darkens with age. Betula nigra is the perfect tree for wet ground. Native to the Southeastern U.S. where it mainly grows along riverbanks in which it is a valuable tree in preventing erosion and it has in fact been a popular tree in Europe for many years because of this. It yields attractive, delicate, diamond shaped, glossy leaves that yellow in the autumn. Its attractive bark is especially interesting in Winter. In Spring, the River Birch can be tapped as one would a maple tree.
I. Appearance and Characteristics
Betula nigra, the black birch, river birch or water birch, is a species of birch native to the Eastern United States from New Hampshire west to southern Minnesota, and south to northern Florida and west to Texas. It is one of the few heat-tolerant birches in a family of mostly cold-weather trees which do not thrive in USDA Zone 6 and up. B. nigra commonly occurs in floodplains and swamps.
Betula nigra is a deciduous tree growing to 25–30 meters (80–100 ft) with a trunk 50 to 150 centimeters (20 to 60 in) in diameter. The base of the tree is often divided into multiple slender trunks.
Bark
Bark characteristics of the river birch differ during its youth stage, maturation, and old growth. The bark of a young river birch can vary from having a salmon-pink to brown-gray tint and can be described as having loose layers of curling, paper thin scales. As the tree matures, the salmon-pink color is exchanged for a reddish-brown with a dark grey base color. The scales on a mature tree lack the loose curling and are closely pressed into thick, irregular plates. These scales are slightly separated from the trunk and can shift outward to the side. Once the river birch ages past maturity, the scales become thicker towards the base of the trunk and are divided in deep furrows.
Leaves and fruit
The twigs are glabrous or thinly hairy. There is an absence of terminal buds, and lateral buds often have a hook at the tip of the bud, which differs from other species in the family Betulaceae. The leaves are alternate, ovate, 4–8 centimeters (1+1⁄2–3+1⁄4 in) long and 3–6 centimeters (1+1⁄4–2+1⁄4 in) broad, with a serrated margin and five to twelve pairs of veins. The upper surface of the leaf is dark green in color, while the underside can be described as having a light yellow-green color. The leaves turn yellow in Autumn. The flowers are wind-pollinated catkins 3–6 centimeters (1+1⁄4–2+1⁄4 in) long, the male catkins pendulous, the female catkins erect. The fruit is unusual among birches in maturing in late spring; it is composed of numerous tiny winged seeds packed between the catkin bracts.
II. How to Grow and Care
Sunlight
Plant river birch trees in full sun (at least six hours of direct sunlight on most days) to part shade locations.
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 favor cooler climates. Still, river birch performs better in regions without blistering summers, and warm climates may shorten its lifespan. It is most prevalent in the humid areas of the eastern U.S., where it is often found in flood plains and swampy areas. This tree prefers humid weather over dry climates.
Watering
Unless the tree grows 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.
Soil
This tree is best planted where the soil is consistently moist or 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.
Fertilizing
You can use any commercial or organic fertilizer for your river birch, if it’s growing slowly. To make sure the roots absorb the fertilizer, irrigate the area beneath the tree and supply granular fertilizer through the drip line.
Pruning
River birch is a self-pruning tree. it will easily shed branches that are diseased or unhealthy, making it require very little maintenance. If you are pruning, river birch is best pruned in fall and winter. Avoid early spring pruning while the tree’s sap is running. Bronze birch borers are out in full force in late spring and early summer 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.
Propagation
Cuttings
Most people don’t want to wait many years to propagate a real tree, but birch trees are fast-growing enough that you won’t need to wait decades to see real results. If you want to try it, river birch is a relatively easy tree to reproduce, either by collecting and planting the seeds or by taking stem cuttings and rooting them. Here’s how to propagate through cuttings:
- As new growth begins in early spring, use sharp pruners to take 6- to 8-inch cuttings from new wood near the tips of the stems, where new wood joins old wood. Ensure the cutting has several leaf nodes, then remove all but the top one or two leaves.
- The failure rate for propagating from cuttings can be high, so it is best to take at least five cuttings to ensure one develops roots and grows into a sapling.
- 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 moisten the soil until new leaves sprout. Grow it in the pot until the tree is large enough to plant in the garden.
Seed
The best way to propagate by seed is to collect catkins from the tree in early spring. Catkins are the flower clusters that contain the fruit, or in this case, nutlets. The nutlets are the seeds.
- Crush the catkins to release the seeds. Remove the papery outer hull of the seed.
- Place a seed in moistened sand in a zipper-lock bag in the refrigerator for two months; keep the sand moist throughout the period.
- Place the seeds in pots filled with potting soil (or a loamy, sandy mixture), scatter a thin layer of potting mix on top, and keep them in bright conditions (16 hours a day or more) until they germinate and sprout. It is best to keep the temperature in the 80s during the day and 70s at night.
- Never allow the soil to dry out.
- Germination should occur within four to six weeks.
- Keep the sprout moist and continue providing warmth as the seedling grows.
- Continue growing in pots until they are large enough to transplant into the landscape. They can also be planted directly in garden soil in your chosen locations.
- These trees readily self-seed, and it’s also an easy matter to transplant the young volunteers.
Overwintering
River birch generally overwinters without incident when planted within its established hardiness range. However, these thin-barked trees 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.
Pests and Diseases
Common Pests and Plant Diseases
Another benefit of river birch is that it is one of the more trouble-free birch species. River birch trees are a good choice when other birch trees have proved problematic; it rarely suffers from diseases and pests. Occasional issues with aphids or fungal leaf-spot diseases may occur but are rarely serious. However, seldomly, it will get affected by more serious issues, including:
- 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. A professional best applies these chemicals.
- This tree is more resistant to the bronze birch borer (Agrilus anxius) than other birch species but 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 a professional applies may defeat bronze birch borer if the damage is not 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 to keep the tree healthy and tolerate minor illnesses. 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, carefully nurture the tree’s overall health, ensuring it gets plenty of water. Have the tree examined for bronze birch borers and treat it if necessary.
Common Problems
A healthy river birch will be relatively trouble-free—they are not fussy and are easy to care for. When problems occur, it is usually because the tree has been planted in less-than-ideal circumstances.
Yellowing Leaves
In the case of river birch, yellowing leaves are usually a symptom of iron chlorosis, a condition in which too alkaline soil 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 notice a large, formerly healthy river birch begin to decline when no environmental changes are evident. In that case, you may be witnessing natural behavior—the tree may be reaching the end of its life expectancy. These are not long-lived trees, and it may be time to remove your tree and replace it with another.
Leaves Drop
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 quickly recover.
III. Uses and Benefits
- Ornamental uses
River birch is a deciduous tree or shrub that is prized for its attractive multicolored peeling bark. The green leaves are also striking, especially when they turn shades of yellow in fall. This is best grown as a specimen tree or a shade tree on lawns in larger gardens or public spaces. It also looks great in cottage gardens and informal gardens. Shade-loving plants like ferns are a great choice for underplanting this birch.
- Other uses
Native Americans used the boiled sap as a sweetener similar to maple syrup, and the inner bark as a survival food. The river birch is not typically used in the commercial lumber industry, due to knotting, but its strong, closely grained wood is sometimes used for local furniture, woodenware, and fuel.
The essential oils derived from leaves, inner bark, and buds of B. nigra are mostly composed of eugenol, linalool, palmitic acid, and heptacosane with many more compounds in smaller concentrations. The combined essential oils are phytotoxic to lettuce (Lactuca sativa) and perennial ryegrass (Lolium perenne) seedlings. They have also demonstrated insecticidal, nematicidal, and antibacterial properties.
