The sweet birch can grow into a shrub or a medium-sized deciduous tree. Its wood is prized for its density and is used in millwork, cabinetry, and furniture. Sweet birch was also the source of wintergreen oil before 1950, synthetic oil of wintergreen appeared. It will attract birds and butterflies like green comma(Polygonia faunus).
I. Appearance and Characteristics
Betula lenta (sweet birch, also known as black birch, cherry birch, mahogany birch, or spice birch) is a species of birch native to eastern North America, from southern Maine west to southernmost Ontario, and south in the Appalachian Mountains to northern Georgia.
Betula lenta is a medium-sized deciduous tree reaching 30 m (98 ft) tall, exceptionally to 35 metres (115 ft) with a trunk up to 60 cm (2.0 ft) diameter. Heights of 50 feet (15 m) to 80 feet (24 m) are more typical. In younger trees the bark is characteristic of most birches, with smooth bark and distinct horizontal lenticels. It is sometimes mistakenly identified as a cherry tree. In older tree specimens the bark (unlike the more commonly known birches) develops vertical cracks into irregular scaly plates revealing rough dark brown bark patterns.
This, however, only occurs in mature, or ancient, trees and these specimens are not often identified by the public as B. lenta due to the difference between the tree’s smooth young bark (which the public is most familiar with) and the tree’s rough, cracked and plated mature bark. The twigs, when scraped, have a strong scent of wintergreen due to methyl salicylate, which is produced in the bark. The leaves are alternate, ovate, 6–15 cm (2.4–5.9 in) long and 4 to 8 cm (1.6–3.1 in) broad, with a finely serrated margin.
The flowers are wind-pollinated catkins 2.5–3 cm (0.98–1.2 in) long, the male catkins pendulous, the female catkins erect. The fruit, maturing in fall, is composed of numerous tiny winged seeds packed between the catkin bracts. Seed production mainly occurs in trees that are between 40 and 200 years old, although light crops may occur as early as 15 years and as long as the tree lives.
The oldest known B. lenta has been confirmed to be 368 years old, and the species may live even longer in an undisturbed ancient forest. Due to the cracking and developing of bark plates, a rough age estimate can be determined by how many bark layers a tree has. Generally the tree’s smooth young bark begins to split around 40–50 years of age, and then begins to peel off the trunk around the age of 70-80. It is then replaced by another layer of bark, which will begin to peel at around 130–150 years. The third layer will peel when the tree has reached 200–210 years and achieved “old growth” status. This will continue to occur as long as the tree lives, but the individual bark layers become indiscernible after roughly 250 years of age.
Black birch seeds at a prolific rate and quickly colonizes disturbed areas. In the Northeastern US in the 1980s, infestations of spongy moths, Hemlock woolly adelgid, and Discula destructiva killed many trees, and their place was taken by black birch.
II. How to Grow and Care
Sunlight
The perfect location for sweet birch receives 6-8 hours of sunlight with shaded, cool soil. This is very important, as sweet birch has a relatively shallow root system and is thus sensitive to soil overheating or drought.
If you’re in the northern hemisphere, the perfect spot for sweet birch cultivation is between the northern and the eastern side of a house, where the building can provide afternoon shade. Avoid western and southern sides, as the strong afternoon sun can dry the soil and negatively affect the tree’s root system. Keep in mind that existing trees and other structures can provide afternoon shading. (If you’re in the southern hemisphere, plant on opposite side.)
Temperature
Sweet birch needs plenty of water and is somewhat sensitive to extreme moisture fluctuations. Most plants in genus Betula are adapted to temperate (and some species to moist) climates. Most of them grow best on moist but not wet soil. Avoid planting your tree in areas that are poorly drained or occasionally flooded, even for short periods.
Watering
Newly planted sweet birch can be sensitive to too little or too much water, so watering 30 seconds twice a week should be enough. The important thing to keep in mind is that the soil should be moist, which means not too dry or soaking wet. Once the tree is established, there is no need to water, except in a hot summer. In summer, lay a hose on the base of the tree and water in a mild stream, allowing water to slowly run over the root system.
Soil
Plant sweet birch in an area with acidic soil protected from compression. It develops a shallow root system that can be easily damaged by soil disturbance. It is very important to choose a good planting site and avoid areas prone to soil compression, such as driveways or pathways. Avoid wet soils that harm the root.
Plants in genus Betula grow best on somewhat acidic soils, with pH of 5.0-6.5, although this can vary from species to species. For example, the white-barked birch, such as paper birch (B. papyfera), can grow on alkaline soils. On the other hand, river birch (B. nigra) will likely show symptoms of iron chlorosis (yellow coloration of the leaves) in alkaline soils. Avoid planting any river birch in soil with a pH higher than 6.5.
Test your soil before you select your birch species (soil tests are available for purchase at most tree nurseries). If the tree has already been planted in soil that is slightly more acidic or alkaline, the soil can be amended. However, it can be complicated and expensive to keep these levels throughout the lifespan of a tree.
Fertilizing
If the soil is alkaline or lacks certain nutrients, fertilize every spring and summer. Most species grow best in somewhat acidic soils with a pH value between 5.0 and 6.5. Slow-release fertilizer should be used. Fertilizer spikes are convenient and simple to use. However, you should fertilize only after a soil test determines that the substrate is lacking in nutrients.
Fertilize in early spring or summer, as this is the peak growth period when a tree requires the most nutrients. Avoid fertilizing the tree in mid-fall, as a late flush of growth may not harden before the winter and expose the young tissue to frost damage.
Planting Instructions
The planting location should ideally provide 6-8 hours of sunlight daily, while keeping the soil shaded, cool, and moist. The tree should be planted in a square-shaped hole 25 cm deeper than the tree’s root ball. A young tree should be supported by tying it (not too tightly) to a wooden stake or rebar with a rubber or a nylon band.
Pruning
Sweet birch should not be pruned in late winter or early spring just before its dormancy period ends. This is because heavy sap flow and open wounds attract birch tree borers in their egg-laying season. Removing more than 25% of the total tree canopy will most likely result in tree death or seriously reduced growth, as with lost photosynthetic surface, the tree loses the ability to synthesize its nourishment. Also, removing too much of the canopy can expose the tree base and roots to too much sunlight.
Prune your sweet birch in late summer or early winter. If performed properly, pruning is very beneficial, as removing dead or infected branches, closely growing branches, and branches protruding out of the canopy increases the overall health of the tree, reduces tree infections, and improves the aesthetic appearance. Remember to disinfect the pruners before you move to the next branch in order to minimize the risks of contamination.
III. Uses and Benefits
- Ornamental uses
This decorative, sweet-scented, and long-lived birch fits in perfectly in many natural-looking landscaping projects, including cottage gardens and wildlife gardens. It would make an excellent ornamental specimen tree that supports butterflies, wild bees, and other pollinators with its leaves and pollen. Additionally, sweet birch is salt-tolerant, making it a suitable candidate for coastal gardens.
- Other uses
The wood of black birch is heavy at 47 pounds per cubic foot and is used for furniture, millwork, and cabinets. It is similar to yellow birch wood and often not distinguished from it in the lumber trade.
The sap flows about a month later than maple sap, and much faster. The trees can be tapped in a similar fashion, but must be gathered about three times more often. Birch sap can be boiled the same as maple sap, but its syrup is stronger (like molasses). It can be used to make birch beer. Boiling also destroys volatile quantities of wintergreen oil.
The inner bark can be eaten raw as an emergency food. The twigs and inner bark can be steeped to make tea.
Black birch was once harvested extensively to produce oil of wintergreen, the tree was borderline endangered until the 1950s-60s when synthetic oil of wintergreen appeared.
