Sweet Birch (Black Birch)

Size, growth and what to expect

Sweet birch can move fast on the right ground. Forest trees have measured 46 feet at age 20 in western Pennsylvania and central West Virginia, and only 6 feet at age 12 in northwestern Pennsylvania. Young trees grow rapidly, and our growth estimator models it as a medium tree, roughly a foot and a half a year in its youth on an average site. In a yard expect 40 to 70 feet, and 70 to 80 feet on the best forest sites.

Flowers open in April and May, and a bearing tree drops a large seed crop every 1 or 2 years. The oldest known tree has been ring-counted to 378 years. Most begin to decline at about 150 years. The leaves feed the caterpillars of the mourning cloak, dreamy duskywing and tiger swallowtail. Black birch is its other name, and sweet comes from the wintergreen aroma of crushed leaves and broken twigs.

It grows wild from southern Maine and Quebec west to eastern Ohio and south from Pennsylvania through the Appalachians to northern Alabama and Georgia, best on moist, protected north and east slopes.

How to grow Sweet Birch

Sweet birch grows in full sun or part shade in moist, acid, well-drained soil. It takes rocky or thin ground but not compacted soil or a hot paved strip, and likes a cool north or east slope. Its crown spreads 35 to 40 feet, so plant it 25 feet from the house. Set trees 35 to 40 feet apart.

Plant a dormant bare-root or potted sapling from leaf fall until bud swell, in a hole wider than the roots and no deeper. Set the flare at the soil line, put the native soil back in, and keep mulch off the trunk. The seed needs light. Gather the cones in September as they turn brown, and sow the seed on the surface of a flat of moist mix, barely covered, left outdoors for the winter. For spring, give it 4 to 8 weeks in a damp bag in the refrigerator first. It comes up over 4 to 6 weeks and wants light shade its first summer.

Water weekly the first two summers when rain is short. Deer mostly leave sweet birch alone, though birches as a group are among the foods they favor in the Northeast. Bucks rub smooth young trunks in fall, and rabbits and voles gnaw thin bark under snow. Cage it for three winters and keep the mulch thin at the stem. Prune in summer or after leaf fall; a birch cut in spring bleeds sap.

Growth is moderate to fast once it settles in, 46 feet at 20 years in Pennsylvania and West Virginia forests, and the first catkins come at 10 to 15 years. Male and female catkins share a tree and the wind carries the pollen, but the one sweet birch tested with its own pollen set no seed, so plant two or more for seed. Leaf miners and skeletonizers mark the leaves some years. A sunken dead patch of bark on the trunk is Nectria canker, which sweet birch gets more readily than most trees; cut out cankered limbs.