Other names for black spruce (Picea mariana) include bog spruce, shortleaf black spruce, and swamp spruce. And just like you’d guess from the name, it loves soggy habitats. It also happens to be the provincial tree of Newfoundland.
I. Appearance and Characteristics
Picea mariana, the black spruce, is a North American species of spruce tree in the pine family. It is widespread across Canada, found in all 10 provinces and all 3 territories. It is the official tree of the province of Newfoundland and Labrador and is that province’s most numerous tree. The range of the black spruce extends into northern parts of the United States: in Alaska, the Great Lakes region, and the upper Northeast. It is a frequent part of the biome known as taiga or boreal forest.
The Latin specific epithet mariana means “of the Virgin Mary”.
P. mariana is a slow-growing, small upright evergreen coniferous tree (rarely a shrub), having a straight trunk with little taper, a scruffy habit, and a narrow, pointed crown of short, compact, drooping branches with upturned tips. Through much of its range it averages 5–15 m (15–50 ft) tall with a trunk 15–50 cm (6–20 in) diameter at maturity, though occasional specimens can reach 30 m (98 ft) tall and 60 cm (24 in) diameter.
The bark is thin, scaly, and grayish brown. The leaves are needle-like, 6–15 mm (1⁄4–9⁄16 in) long, stiff, four-sided, dark bluish green on the upper sides, paler glaucous green below. The cones are the smallest of all of the spruces, 1.5–4 cm (1⁄2–1+1⁄2 in) long and 1–2 cm (1⁄2–3⁄4 in) broad, spindle-shaped to nearly round, dark purple ripening red-brown, produced in dense clusters in the upper crown, opening at maturity but persisting for several years.
Natural hybridization occurs regularly with the closely related P. rubens (red spruce), and very rarely with P. glauca (white spruce).
It differs from P. glauca in having a dense cover of small hairs on the bark of young branch tips, an often darker reddish-brown bark, shorter needles, smaller and rounder cones, and a preference for wetter lowland areas. Numerous differences in details of its needle and pollen morphology also exist but require careful microscopic examination to detect. From true firs, such as Abies balsamea (balsam fir), it differs in having pendulous cones, persistent woody leaf-bases, and four-angled needles, arranged all round the shoots.
Due to the large difference between heartwood and sapwood moisture content, it is easy to distinguish these two wood characteristics in ultrasound images, which are widely used as a nondestructive technique to assess the internal condition of the tree and avoid useless log breakdown.
Older taxonomic synonyms include A. mariana, P. brevifolia, or P. nigra.
II. How to Grow and Care
Black spruce is a hardy conifer that generally requires minimal maintenance, making it an easy-to-care-for species. It thrives in cooler climates and well-drained, acidic soils, and necessitates full sunlight exposure for optimal growth. A special care point for black spruce includes ensuring protection from wind as it can be vulnerable to strong gusts. Regular watering during dry periods will support black spruce’s health but avoid overwatering to prevent root rot.
Sunlight
Black spruce thrives in full sunlight where the intensity of light promotes robust growth and ensures optimal health. The species is well-adapted to long durations of daylight, which is critical for its photosynthesis process. While black spruce prefers direct sunlight, it exhibits a notable tolerance for partial sun conditions, although reduced light levels can lead to a slower growth rate and potential for less dense foliage. Black spruce is resilient to variations in light, but consistency in the optimal light setting is preferred to maintain its vigor. Outdoor planting for black spruce should prioritize open areas where direct sunlight is abundant to support its development.
Temperature
Black spruce likes cool and moist climates. The ideal temperature range for tree growth is 4 to 18 ℃. It’s hardy and tolerant of temperatures as low as -30 ℃, but young trees and tender branches are less cold-resistant.
Black spruce likes moisture, it has good adaptability and is slightly drought-enduring. During the spring and summer growing seasons, the tree prefers higher air humidity (70-80%), while in the fall and winter, lower air humidity (55-65%) can help it grow more sturdy.
Watering
Adapted to the cooler climates and boggy conditions of its native habitat, black spruce thrives with moderate moisture. This species exhibits a preference for consistent humidity levels, indicative of its resilience in wetter environments. Watering is optimal once every 1-2 weeks, aligning with its ability to tolerate short periods of dryness. Typically found in outdoor settings, black spruce has adapted to endure the seasonal fluctuations in water availability that characterize its native boreal forests.
Soil
Black spruce grows well in fertile, deep, well-drained, slightly acidic soils. The best soil pH range is 5.1-7.3, making both sandy soil or slightly clay-like soil good choices. As the tree grows slowly and has a long life span, the soil layer should be about 70 cm thick. If barren, the soil can be improved by adding nutrient soil or organic manure.
Fertilizing
To maintain black spruce’s health, apply balanced nutrition fertilizers biannually in spring and fall, fostering robust growth and resilience. Use a slow-release formula at the label-recommended rate, ensuring a consistent nutrient supply. Young black spruce benefits from more frequent feedings, aiding in establishment. Avoid over-fertilization to prevent growth issues and environmental harm. Always water black spruce thoroughly post-application to facilitate nutrient absorption and protect roots. Seasonal adjustments are crucial for optimal care.
Pruning
Black spruce has lush terminal buds. The tree usually takes on a beautiful triangular shape and does not require pruning in general. When overly pruned, its incisions secrete rosin excessively which affects the tree’s normal growth. It’s best to trim off overly dense, diseased, and dried branches during the plant’s winter dormancy. Prune and beautify the treetop in early spring when buds sprout. About 1/2 of the young branches can be pruned off to create your desired shape. For large, mature trees, it’s a good idea to prune off all the branches on the lower trunk to reduce nutrition consumption.
When growing black spruce for Christmas decorations, you need to control height and width. Prune the treetop and lateral branches appropriately short and continue to cut the newly-grown buds short, as well. Repeat this process many times. Seal pruning incisions with wax or duct tape to keep rosin from effusing.
Propagation
A hardy, versatile conifer, black spruce thrives in cooler climates with its dense foliage and conical shape. Propagation by sowing is effective for enthusiasts seeking to cultivate black spruce. Start with fresh seeds and use a well-draining seed starting mix. The ideal germination environment is cool and moist, simulating black spruce’s natural habitat. Sow seeds shallowly, as light aids in germination. Maintain consistent moisture, but avoid waterlogging. Under optimal conditions, seeds will typically germinate within a few weeks to a couple of months, leading to the successful growth of young black spruce plants.
Transplanting
For black spruce, the cusp of warm season—late spring to early summer—is ideal, ensuring a gentle establishment before winter. Aim for a moist, acidic soil location, shaded, and keep the root ball intact to encourage stability.
III. Uses and Benefits
Black spruce is the provincial tree of Newfoundland and Labrador.
The timber is of low value due to the small size of the trees, but it is an important source of pulpwood and the primary source of it in Canada. Fast-food chopsticks are often made from black spruce.
However, it is increasingly being used for making cross laminated timber by companies such as Nordic Structures, which allows the high strength due to the tight growth rings to be assembled into larger timbers.
Along with red spruce, it has also been used to make spruce gum and beer.
