The sitka spruce (Picea sitchensis) is the fifth-tallest conifer in the world and can grow to be 70 m tall. Sitka spruce is found in cool, maritime locations in coastal areas. This species grows best in deep, moist, well-drained soil. It produces reddish to yellowish-brown seed cones. Its light, soft wood is strong and flexible, with acoustic qualities. This tree’s wood is commercially used to make musical instruments such as guitars and pianos. It is also used to make early aircraft and boats.
I. Appearance and Characteristics
Picea sitchensis, the Sitka spruce, is a large, coniferous, evergreen tree growing to almost 100 meters (330 ft) tall, with a trunk diameter at breast height that can exceed 5 m (16 ft). It is by far the largest species of spruce and the fifth-largest conifer in the world (behind giant sequoia, coast redwood, kauri, and western red cedar), and the third-tallest conifer species (after coast redwood and coast Douglas fir).
The bark is thin and scaly, flaking off in small, circular plates 5–20 centimeters (2–8 in) across. The inner bark is reddish-brown. The crown is broad conic in young trees, becoming cylindric in older trees; old trees may not have branches lower than 30–40 meters (98–131 ft). The shoots are very pale buff-brown, almost white, and glabrous (hairless), but with prominent pulvini. The leaves are stiff, sharp, and needle-like, 15–25 millimeters long, flattened in cross-section, dark glaucous blue-green above with two or three thin lines of stomata, and blue-white below with two dense bands of stomata.
The cones are pendulous, slender cylindrical, 6–10 cm (2+1⁄2–4 in) long and 2 cm (3⁄4 in) broad when closed, opening to 3 cm (1+1⁄4 in) broad. They have thin, flexible scales 15–20 mm (5⁄8–3⁄4 in) long; the bracts just above the scales are the longest of any spruce, occasionally just exerted and visible on the closed cones. They are green or reddish, maturing pale brown 5–7 months after pollination. The seeds are black, 3 mm (1⁄8 in) long, with a slender, 7–9 mm (1⁄4–3⁄8 in) long pale brown wing.
Size
More than a century of logging has left only a remnant of the spruce forest. The largest trees were cut long before careful measurements could be made. Trees over 90 m (300 ft) tall may still be seen in Pacific Rim National Park and Carmanah Walbran Provincial Park on Vancouver Island, British Columbia (the Carmanah Giant, at 96 m (315 ft) tall, is the tallest tree in Canada), and in Olympic National Park, Washington and Prairie Creek Redwoods State Park, California (United States), the latter of which houses the tallest individual measuring at 100.2 meters or 329 feet tall; two at the last site are just over 96 m tall. The Queets Spruce is the largest in the world with a trunk volume of 346 m3 (12,200 cu ft), a height of 74.6 m (244 ft 9 in), and a 4.4 m (14 ft 5 in) dbh. It is located near the Queets River in Olympic National Park, about 26 km (16 mi) from the Pacific Ocean. Another specimen, from Klootchy Creek Park, Oregon, was previously recorded to be the largest with a circumference of 15 metres (49 ft) and height of 66 metres (217 ft).
Age
Sitka spruce is a long-lived tree, with individuals over 700 years old known. Because it grows rapidly under favorable conditions, large size may not indicate exceptional age. The Queets Spruce has been estimated to be only 350 to 450 years old, but adds more than a cubic meter of wood each year.
Root system
Because it grows in extremely wet and poorly-drained soil, the Sitka spruce has a shallow root system with long lateral roots and few branchings. This also makes it susceptible to wind throw.
Sitka spruce is native to the west coast of North America, with its northwestern limit on Kenai Peninsula, Alaska, and its southeastern limit near Fort Bragg in northern California. It is closely associated with the temperate rainforests and is found within a few kilometers of the coast in the southern portion of its range. North of Oregon, its range extends inland along river floodplains, but seldom does its range extend more than around 80 km (50 mi) from the Pacific Ocean and its inlets. It is situated at about 2,500 m (8,200 ft) above sea level in Alaska and generally below 450 m (1,480 ft) further south.
II. How to Grow and Care
Sunlight
Sitka spruce thrives in conditions of full sun, where the light intensity is high and direct for most of the day. This optimal lighting plays a crucial role in its vigorous growth and health, allowing for efficient photosynthesis. In terms of light tolerance, sitka spruce can also adapt to partial sun, although its growth may be somewhat less vigorous in these conditions. Under lower light, sitka spruce might exhibit signs of stress or slower growth rates. Outdoors, sitka spruce should be planted in a location that receives unfiltered sunlight for the majority of the day to ensure it meets its light requirements for optimal health.
Temperature
Sitka 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.
Sitka 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
Originating from the moist, cool climates of the North Pacific coast, sitka spruce thrives in environments with consistent moisture. This species exhibits a preference for regular hydration but can tolerate short periods of dryness. Watering is optimal once every 1-2 weeks, ensuring soil remains damp but not waterlogged. As an evergreen plant commonly grown outdoors, sitka spruce benefits significantly from natural rainfall patterns, which help maintain its lush foliage throughout various climate zones.
Soil
Sitka 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
For optimal care of sitka spruce, use balanced nutrition fertilizers such as a 10-10-10 mix. Spring and early summer are key times for fertilization to support growth. Apply fertilizer at the tree’s drip line, not near the trunk, at a rate of 2 lbs per inch of trunk diameter once yearly. Over-fertilization can lead to excessive foliar growth at the expense of root development. Adjust amounts for young trees or during dormant seasons. Safety tip: Wear gloves and water the area before and after applying fertilizer to help root absorption and prevent root burn.
Planting Instructions
To grow sitka spruce in a yard, purchase seedlings and transplant them in early spring. Get the planting pit ready one week before transplanting; its diameter needs to be about 20 cm longer than that of the root ball and have a depth of about 15 cm deeper. It should be no less than 6 m away from other plants. Add organic fertilizers to the bottom of the planting pit before transplanting and mix them well with the soil.
Place the seedling vertically into the pit, shovel 2/3 of the soil back, and water thoroughly once to make sure the moisture around the plant’s roots is sufficient. Then, fill the pit fully up with soil and water again. Stomp the soil firmly and keep the pit surface level with the ground. If it’s often windy at the planting site, support the young tree with wood sticks or metal poles in case a strong gale threatens to tilt it or knock it down.
Indoor potted sitka spruce can be directly purchased. The tree grows slowly and usually doesn’t require repotting. Repotting is only necessary if the needles turn yellow and fall off the tree, the roots around the pot brim or at the bottom wither and dry up, or the soil in the pot compacts. Move the majority of the original soil to the new pot with the plant, and add small amounts of organic fertilizers and new soil to provide more nutrients for its growth.
Pruning
Sitka 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 sitka 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
Sitka spruce is best propagated during Autumn and Winter using methods such as layering, cutting, and sowing. Although propagation can be moderately difficult, success is indicated by new root growth and sprouting foliage. Ensure optimal hydration during the process.
Transplanting
Spring to early summer is ideal for transplanting sitka spruce, as the mild temperature and plentiful rainfall promote root growth. Sitka spruce thrives in damp, well-drained soil with exposure to sunlight and occasional shade. If stressed, consider shading and frequent watering. Remember, ensure the new climate is similar to sitka spruce’s indigenous one for successful transplantation.
Repotting
Repot your sitka spruce every 2-3 years to accommodate its growth. Best done in early spring, repotting gives the large, conical evergreen the space needed to expand. Choose a large container that allows room for the root system. After repotting, ensure sitka spruce gets plenty of sunlight and avoid overwatering to help it thrive.
III. Uses and Benefits
- Ornamental uses
Famous for being the largest spruce of them all, sitka spruce is rarely found in the garden setting precisely due to its size. However, on properties big enough to accommodate it, it can work great on exposed sites or on patches with poor soil. Because it is more salt spray-tolerant than many of its conifer cousins, sitka spruce can also be used in coastal landscaping.
- Culinary uses
Newly grown tips of Sitka spruce branches are used to flavor spruce beer and are boiled to make syrup.
- Other uses
The root bark of Sitka spruce trees is used in Native Alaskan basket-weaving designs and for rain hats. The pitch was used for caulking, chewing, and its medicinal properties. Native Americans heated and plied the roots to make cord. The resin was used as glue and for waterproofing. Natives and pioneers split off shakes for construction use. The wood is light and relatively strong.
Sitka spruce is of major importance in forestry for timber and paper production. Outside its native range, it is particularly valued for its fast growth on poor soils and exposed sites where few other trees can prosper; in ideal conditions, young trees may grow 1.5 m (5 ft) per year. It is naturalized in some parts of Ireland and Great Britain, where it was introduced in 1831 by David Douglas, and New Zealand, though not so extensively as to be considered invasive. Sitka spruce is also planted extensively in Denmark, Norway, and Iceland. In Norway, Sitka spruce was introduced in the early 1900s. An estimated 50,000 hectares (120,000 acres) have been planted in Norway, mainly along the coast from Vest-Agder in the south to Troms in the north. It is more tolerant to wind and saline ocean air, and grows faster than the native Norway spruce. But in Norway, the Sitka spruce is now considered an invasive species, and efforts to eliminate it are being made.
The resonant wood is used widely in piano, harp, violin, and guitar manufacture, as its high strength-to-weight ratio and regular, knot-free rings make it an excellent conductor of sound. For these reasons, the wood is also an important material for sailboat spars, and aircraft wing spars (including flying models). The Wright brothers’ Flyer was built using Sitka spruce, as were many aircraft before World War II; during that war, aircraft such as the British Mosquito used it as a substitute for strategically important aluminium.
