Black spruce, Picea mariana, is an ideal evergreen to plant in wet, soggy soil, because that’s where you’ll typically find it in northern forests. Also known as bog spruce, swamp spruce, eastern spruce and shortleaf black spruce, this pyramid-shaped evergreen conifer is small to medium sized with shallow, far-reaching roots. Its small, purplish cones may be its most striking feature, though these do turn brown as seeds mature.
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In nature the black spruce thrives in cool uplands, especially poorly drained, acidic peat bogs, but you’ll also find it along streams and near the edges of swamps. It does best in full sun but tolerates shade and low levels of nutrients in soil. It can be seriously afflicted by eastern dwarf mistletoe, which can sap tree strength and cause deformities and death. Black spruce is also vulnerable to wood borers, spruce budworm, snow blight, fungi and needle rust.
The black spruce is very cold hardy--to Zone 2--and can live up to 200 years. It grows to 30 or 40 feet tall, features an open, irregular crown and has a trunk diameter of 6 to 18 inches. Lower branches often brush the ground, and through “natural layering” will form new trees where growing tips successfully root. Otherwise, black spruce branches are short and pendulous, with a tendency to curve upward at their tips. Bark is gray-brown with thin surface scales, and twigs are hairy. Black spruce needles are short, four-sided, dull blue-green and soft and flexible. Cones are oval, up to 1 inch long and tend to stay on the tree for years.
Cones & Seeds
Black spruce trees produce both male and female flowers, usually in late May or early June. Male flowers are produced on the crown’s outer branches and are usually a half-inch long and purple or dark red. Flowers are erect green or purple cylinders about an inch long. “Conelets” develop rapidly from these female flowers, with mature seeds produced within several months. Maximum cone and seed production begins when trees reach 100 years old, with a “heavy seed year” occurring every two to six years.
As a landscape tree, the black spruce’s shallow roots make it a good candidate for thin soils over bedrock. But think twice before planting it in areas vulnerable to wildfires; its thin bark and shallow roots make it unlikely to survive. Though it is an excellent candidate for soggy, bog-like acidic soils--unlike most other evergreens--it may not survive flooding and substantial groundwater fluctuations. Black spruce trees are sometimes grown as Christmas trees. Wood of the black spruce is soft, lightweight and strong, used as framing and construction lumber, for planking and for pulp. Needles are distilled for perfume and as a key ingredient of spruce beer.
Black spruce is greatly appreciated by wildlife. In nature it provides good cover for moose and other large mammals. It also serves as a food source for spruce grouse, snowshoe hare, red squirrels, various mice species, voles, shrews, chipmunks and birds. A number of different bird species also nest in the tree, or use tree materials for building nests.