White Spruce Tree (Picea Glauca)

White spruce (Picea glauca) is a tree native to North America and growing widely throughout Alaska and Canada. White spruce is the symbolic tree of Canada’s Manitoba province and the state of South Dakota in the United States. Commercially, its wood is used to make paper and materials for construction projects. This tree can be grown as a bonsai.

I. Appearance and Characteristics

Picea glauca, the white spruce, is a species of spruce native to the northern temperate and boreal forests in North America. Picea glauca is native from central Alaska all through the east, across western and southern/central Canada to the Avalon Peninsula in Newfoundland, and south to Montana, North Dakota, Minnesota, Wisconsin, Michigan, Upstate New York and Vermont, along with the mountainous and immediate coastal portions of New Hampshire and Maine, where temperatures are just barely cool and moist enough to support it.

There is also an isolated population in the Black Hills of South Dakota and Wyoming. It is also known as Canadian spruce, skunk spruce, cat spruce, Black Hills spruce, western white spruce, Alberta white spruce, and Porsild spruce.

The white spruce is a large evergreen conifer which normally grows to 15 to 30 metres (50 to 100 ft) tall, but can grow up to 40 m (130 ft) tall with a trunk diameter of up to 1 m (3 ft 3 in). The bark is thin and scaly, flaking off in small circular plates 5 to 10 centimetres (2 to 4 in) across. The crown is narrow – conical in young trees, becoming cylindrical in older trees. The shoots are pale buff-brown, glabrous in the east of the range, but often pubescent in the west, and with prominent pulvini. The leaves are needle-like, 12 to 20 millimetres long, rhombic in cross-section, glaucous blue-green above (hence glauca) with several thin lines of stomata, and blue-white below with two broad bands of stomata.

The cones are pendulous, slender, cylindrical, 3 to 7 cm long and 1.5 cm wide when closed, opening to 2.5 cm broad. They have thin, flexible scales 15 mm long with a smoothly rounded margin. They are green or reddish, maturing to pale brown 4 to 8 months after pollination. The seeds are black, 2 to 3 mm long, with a slender, 5 to 8 mm long pale brown wing.

• Seeds

Seeds are small, 2.5 to 5 mm long, oblong, and acute at the base. Determinations of the average number of sound seeds per white spruce cone have ranged from 32 to 130.

Common causes of empty seed are lack of pollination, abortion of the ovule, and insect damage.

The average weight per individual seed varies from 1.1 mg to 3.2 mg.

Each seed is clasped by a thin wing 2 to 4 times as long as the seed. Seed and wing are appressed to the cone scale. Embryo and megagametophyte are soft and translucent at first; later the endosperm becomes firm and milky white, while the embryo becomes cream-coloured or light yellow. At maturity, the testa darkens rapidly from light brown to dark brown or black. Mature seeds “snaps in two” when cut by a sharp knife on a firm surface.

White spruce cones reach their maximum size after 800 GDD. Cone moisture content decreases gradually after about 1000 GDD.

Cone colour also can be used to help determine the degree of maturation, but cones may be red, pink or green. Collection and storage dates and conditions influence germination requirements and early seedling growth.

A bushel (35 L) of cones, which may contain 6500 to 8000 cones, yields 6 to 20 ounces (170 to 570 g) of clean seed.

Seed dispersal begins after cone scales reflex with cone maturation in the late summer or early fall of the year of formation. Cones open at moisture contents of 45% to 70% and specific gravities of 0.6 to 0.8. Weather affects both the initiation and pattern of seed dispersal, but cone opening and the pattern of seed dispersal can vary among trees in the same stand. Even after dispersal has begun, cold, damp weather will cause cone scales to close; they will reopen during dry weather. Most seed falls early rather than late, but dispersal may continue through fall and winter and even into the next growing season. Seed dispersal occurs mainly in late summer or early fall.

White spruce seed is initially dispersed through the air by wind. Both the initiation and pattern of seed dispersal depend on the weather, but these can vary among trees in the same stand. Small amounts of white spruce seed are normally dispersed beyond 100 m from the seed source, but exceptionally seeds have been found more than 300–400 m from the nearest seed source.

• Root system

The root system of white spruce is highly variable and adaptable, responding to a variety of edaphic factors, especially soil moisture, soil fertility, and mechanical impedance. On soils that limit rooting depth, the root system is plate-like, but it is a common misconception to assume that white spruce is genetically constrained to develop plate-like root systems irrespective of soil conditions. In the nursery, or naturally in the forest, white spruce usually develops several long ‘running’ roots just below the ground surface.

The structure of the tracheids in the long lateral roots of white spruce varies with soil nitrogen availability.

• Stem

White spruce can live for several hundred years, with an estimated average lifespan of 250 to 300 years.

Slow-growing trees in rigorous climates are also capable of great longevity. White spruce 6 to 10 m (20 to 33 ft) high on the shore of Urquhart Lake, Northwest Territories, were found to be more than 300 years old.

The bark of mature white spruce is scaly or flaky, grey-brown or ash-brown, but silvery when freshly exposed. Resin blisters are normally lacking, but the Porsild spruce Picea glauca var. porsildii Raup has been credited with having smooth resin-blistered bark.

White spruce bark is mostly less than 8 mm and not more than 9.5 mm thick.

Isorhapontin can be found in spruce species such as the white spruce.

P. glauca has three different genomes; a nuclear genome, a mitochondrial genome, and a plastid (i.e. chloroplast) genome. The large (20 Gbp) nuclear genome of P. glauca (genotype WS77111) was published in 2015, and the organellar (plastid and mitochondrial) genomes (genotype PG29) were published in SD Jackman et al. 2015. The plastid genome of P. glauca (genotype WS77111) has also been published.

II. How to Grow and Care

Sunlight

A white spruce will grow and perform its best when planted in full sun. The species can also manage in partial shade without a noticeable impact. Certain cultivars will perform better in certain conditions, which should be noted before you purchase one.

Temperature and Humidity

Possibly the biggest conditional concern of the white spruce, depending on the cultivar, temperature is everything for this northern native. This species loves cold weather; it thrives in frigid winters and cool summers and suffers in the heat. Keeping strict to its USDA hardiness zone recommendations of USDA 2 through 6 will guarantee your white spruce won’t be harmed by the climate.

Be sure to look closely at the plant tags of cultivars, as these may differ from the species recommendations.

Watering

Water can be an issue for the white spruce in certain areas, especially those that can become too warm. Supplemental watering may be needed to keep your white spruce vigorous and attractive if you are in the southern ranges of its habitable zone or are experiencing long stretches of dry weather.

Soil

Other than the ability of its soil to retain and drain moisture, the white spruce is very adaptable when it comes to soil. Unlike some conifers, it is not fussy regarding pH and soil consistency.

Fertilizing

For white spruce, use balanced nutrition fertilizers to boost growth and resilience. Apply biannually, once in spring pre-growth and once in late summer to prep for dormancy. Use according to label instructions, adjusting for plant size. Over-fertilizing can harm roots – less is often more. Growth stage impacts need; young white spruce benefit from more frequent feeding. Incorporate slow-release formulas to maintain steady nutrient supply. Always water thoroughly post-fertilization to aid absorption and reduce risk of burn.

Pruning

There is no need to prune white spruce to shape or form it. It only needs maintenance pruning (removing dead, dying, and damaged branches). They will grow as intended and will only need to be pruned if branches are creating a hazard.

Propagation

White spruce is most easily propagated by cutting or grown from seed. While it is possible to propagate through grafting, this is difficult, so using cuttings and seeds is the most common route for the typical home gardener to propagate the white spruce.

Here’s how to propagate white spruce using cuttings, a process best done in winter or early spring:

• Choose a healthy and green branch; use only established growth.
• Separate the cutting from the main branch with sharp shears. Look for a “node” and lively growth on a branch, then cut between the two.
• Scrape the cutting about an inch from the bottom to remove some bark, then dip the exposed piece in rooting hormone.
• Place the cut end of the branch in a pot filled with damp peat moss and tamp the medium down thoroughly around the base. Use pots at least 5 inches deep and with holes for drainage to allow for better root growth. The cuttings might take up to 6 months to develop their root systems.
• When there is ample root growth, repot to larger pots.

Overwintering

The white spruce will thrive at very low temperatures, and no overwintering is needed. Immature trees will often do better if a thin layer of mulch is placed around their base to help insult their developing roots; mature trees will not need such protection.

Repotting

Repot white spruce, a large conifer, during early spring every 2-3 years to accommodate its growth. Choose a container one size larger with good drainage. After repotting, keep the soil consistently moist and provide ample sunlight. Caution: white spruce requires delicate handling to avoid disrupting its roots during this process.

Pests and Diseases

Relatively disease-resistant trees when in the right conditions, white spruce can become susceptible to plant diseases when exposed to drought or higher than usual temperatures.

Two common fungal diseases that can arise in these conditions are rhizosphaera needle cast (the most common white spruce disease) and cytospora canker. Both diseases share the same symptoms: needles will turn brown in late winter to early spring and begin to drop by summer. Usually, these diseases are not fatal but can be very unsightly.

Ensure plenty of water during droughts to help stem these pathogens; be sure you’re watering the soil around the base of the tree without allowing a backsplash onto the needles. Planting with an appropriate space between trees will also defend against both diseases, as proper airflow will allow needles to dry between watering.

As far as insects go, the wild-type white spruce is very good at holding its own against pests when mature. Cultivars can be more prone to insect damage, so you must take more care and inspect them for signs of pests more often. The most common pests you will find are spider mites and bagworms. Botanical oils and insecticidal soaps can help with the problem.

III. Uses and Benefits

• Ornamental uses

White spruce is an evergreen conifer that has attractive year-round needles that offer good ornamental appeal. This tree doesn’t thrive in polluted urban environments and salty coastal conditions, so it is best suited to rural inland plantings in large ornamental gardens and parks. This is a tall tree that needs lots of space, so it makes a good specimen tree and can also be grown as a windbreak because of its dense foliage. White spruce pairs well with hydrangeas and ornamental grasses.

• Other uses

The wood of white spruce is of a lower quality than that of Engelmann spruce, but is stronger. It was used to make shelters and as firewood by Native Americans and European settlers in Alaska, where lodgepole pine does not grow. The wood is of major economic importance in Canada, being harvested for paper and construction. It is also used as a Christmas tree.

The wood is also exported to Japan where, known as “shin-kaya”, it is used to make go boards as a substitute for the rare kaya wood.

Black Hills spruce (Picea glauca var. densata) is used for bonsai.

White spruce is the provincial tree of Manitoba and the state tree of South Dakota.

The new growth or tips of white spruce is used in beer making, gin production, flavouring pop, candy making or in pickles and preserves.