Spruces, <em>Picea</em>: plant, prune and care for

Description and botany

Les Picea belong to the family Pinaceae, like Pines, Firs, Cedars and Larches. The Latin name of spruce derives from the Latin pix, meaning pitch or resin, which this conifer contains abundantly in its bark, wood, needles and cones, much like Pines.

Spruces occupy humid forests from the Tropic of Cancer in Mexico to northern Siberia, from sea level up to 4 500 m in the Himalayas. Most species grow in shade and provide dense shade themselves, but some tolerate full sun well.

To distinguish Picea from Abies (firs), simply look at the crown of mature specimens, which bear pendulous oblong cones, unlike those of firs. Many natural crosses occur between spruce species that share the same range, which complicates identification. The arrangement of needles on the twig often varies with their position in the tree. Observe well-developed horizontal twigs. Cones often provide the most reliable characters.

Spruces retain a strong apical dominance so that the leading shoot often persists even in old trees, except after lightning strike or in windy sites. The pyramidal silhouette nevertheless varies with species, branch angle, degree of arching upwards or downwards, and crown width — rigid and narrow in Picea omorika, forming flowing curtains in Picea breweriana…

Picea abies – botanical illustration by Koehler (1887)

Norway spruce (Picea abies) is probably the best known, planted extensively in regions such as the Morvan in particular to supply inexpensive “Christmas trees”. It is often found dominating in small gardens where it can overpower surroundings with dense shade, and is recognisable by its regular pyramidal habit with slightly arched branches and its fresh green colour. It grows very fast and easily reaches 36 m in height. It is native to a broad area from the mountains of Scandinavia to north-west Russia via central Europe, and is cultivated as a forest species as far east as the United States. It has produced a number of dwarf varieties much appreciated in gardens, such as Picea abies ‘Acrocona’, noted for a profusion of small bright pink young cones at branch tips, very decorative even on young trees. The Sitka spruce is the other most commonly planted species because of its very rapid growth and low soil and climate demands, allowing it to be grown even in Ireland on peaty moorland. It is native to the west coast of the United States, from California to Alaska — including Sitka, an area with very high rainfall (2 200 mm) and a climate approaching polar conditions similar to the Scottish Highlands. It reaches the greatest heights in the genus at around 70 m with trunks 4–5 m in diameter (a 97 m specimen recorded in British Columbia).

Spruce needles are fairly short (6 to 30 mm), borne singly in a spiral along twigs and are generally quadrangular in cross-section, without white bands of stoma on Picea abies, with exceptions such as Serbian spruce (Picea omorika) and Sitka spruce, which have flattened needles with two white bands beneath. Needles remain on a twig for 7 to 10 years. Pulling on a generally prickly needle will tear off a bit of bark because the needle is decurrent, that is inserted on a small cushion which persists when the needle falls. A fir needle, by contrast, leaves a neat round scar when removed. The shape of the leafy twig resembles a bottlebrush due to the inward curve of the needles towards the top of the horizontal twig. When spruce needles fall after several years they leave a , not pleasant to stroke. This uninviting aspect is offset by the comfort offered by the buttresses at the base of the trunk, which serve as armrests. The bark is scaly and thin, buds are conical, less than 5 mm, and non-resinous.

Male and female flowering of spruces occur on the same tree but on separate inflorescences. Male aments borne in the mid and lower parts of the tree form small erect clubs 10–20 mm long, orange turning yellow when they release pollen in April or May, spectacular in Picea orientalis. Female conelets, borne in the mid and upper parts of the tree, form erect fleshy cones 10–25 mm long, green or purplish-red. Cones with very small bracts become pendulous after fertilisation and fusiform, (12–15 cm in Picea abies), lignified similar to those of firs and much less tough than those of pines, reach ripeness in late summer–autumn and release winged seeds from the top of the tree. Cones of Picea orientalis show a splendid purple colour.

Some spruces: Picea glauca ‘Conica’, Picea pungens ‘Glauca Globosa’, Picea glauca ‘Alberta Globe’ and Picea abies

Wood of Norway spruce is a light-coloured timber valued for frame construction and for pulp. Its bark is still used in Germany for tanning leather while turpentine oil is extracted from its twigs.

A Sitka spruce from ancient forests can produce timber as strong as steel, used for shipbuilding or for soundboards of grand pianos, harps or violins.

Main spruce varieties

Large to medium-growing varieties

Dwarf varieties

Picea jezoensis subsp. hondoensis

Large evergreen tree forming a wide conical crown, with young silver shoots turning green, bearing slender pendulous cones green or reddish and striking red-brown bark. Large-growing species best suited to expansive spaces, or to grow as bonsai. Prefers cool, humid climates and a shaded to part-shaded position.

• Height at maturity 40 m

See the product sheet

Picea pungens Iseli Fastigiate - Blue Spruce

Forms a slender, regular cone, up to 2 m wide, with foliage blue in spring becoming grey-blue-silvery while remaining very bright. Modest size and low-maintenance nature make it ideal for small gardens. Magnificent, undemanding conifer that tolerates pollution, heat and occasional drought once established.

• Height at maturity 7 m

See the product sheet

Picea abies Inversa - Norway Spruce

Distinctive and original habit, forming a narrow column covered with very bright green descending branches, falling like a mane. Trunk disappears completely under a trailing mass that spreads indefinitely. This surprising conifer is planted singly or at the centre of a bed. Prefers sun and thrives in cool, well-drained soil with low lime content.

• Height at maturity 6,50 m

See the product sheet

Picea glauca Sanders Blue - White Spruce

Conical spruce with young metallic grey-blue shoots that in spring cover the older blue-green foliage. Very slow-growing, perfect for rockeries, enlivens beds and performs well in pots. Small, very hardy conifer, enjoying sun and ordinary, cool soils.

• Height at maturity 3 m

See the product sheet

White spruce - Picea glauca Daisys White

Cream form of the famous dwarf spruce Picea glauca 'Conica'. Perfect pyramid covered in very regular foliage. Young shoots, white to pale yellow, in spring overwhelm the older dark green foliage, irresistibly catching the eye. Suitable for rockeries or large pots.

• Height at maturity 1,50 m

See the product sheet

Picea pungens Waldbrunn - Blue Spruce

Excellent dwarf variety with a perfectly rounded, nest-like shape. Foliage blue-grey with silvery reflections. Very slow-growing and compact, suited to rockeries, but also to beds, borders or pots. Thrives in sun or part shade, in well-drained, cool soil, neutral to acidic.

• Height at maturity 70 cm

See the product sheet

Picea omorika Beskid - Serbian Spruce

One of the most interesting varieties, still very hard to find. Globose, almost spherical habit formed by fine, slightly hirsute branches. Suitable for small gardens, large rockeries and pots. Very hardy, undemanding in cool climates, in well-drained but not too dry soils, and in sunny exposure.

• Height at maturity 80 cm

See the product sheet

Picea abies Eagle Point - Norway Spruce

Dwarf variety resembling a small Christmas tree, both by its slightly flattened pyramidal habit and by its fine, dense foliage made up of needles with very vivid blue highlights. Rare and highly ornamental with its small rounded silhouette that fits elegantly into beds, commands attention in isolation, enlivens rockeries and adapts well to container cultivation.

• Height at maturity 50 cm

See the product sheet

Planting

Where to plant spruce?

Spruces appreciate cool, humid atmospheres and dislike atmospheric pollution. They prefer cool soils with an acidic to neutral pH but can tolerate relatively dry soil such as Picea abies or pungens. Picea rubens and pungens both tolerate lime unlike most spruces. Spruces tolerate wind well and have excellent hardiness.

Spruce root system is generally shallow and extensive, so they do not tolerate transplanting well. Spruce forests often planted very densely have no understorey because of dense shade they provide.

If your soil is waterlogged, opt for a variety of Picea mariana (black spruce) or even Picea sitchensis. The latter particularly favours oceanic climate or areas often shrouded in fog, below 500 m altitude, such as Brittany, Normandy, Massif Central, Béarn or Basque Country.

Growth is slow in Picea glauca or Picea rubens whereas it can be very rapid in most other species, except dwarf cultivars.

Picea abies ‘Little Gem’ / Picea glauca ‘Sander’s Blue’

When to plant?

Prefer autumn, October–November, to plant spruces so roots can spread well before summer, otherwise in February–March.

How to plant?

If planting a large specimen, it may be vulnerable to windthrow and have difficulty establishing (except Sitka spruce, which is easy to transplant).

• Immerse pot in a bucket of water to thoroughly moisten it.
• Dig a wide hole at least three times wider than rootball because roots remain fairly shallow and spread widely.
• Avoid planting spruce too close to a bush bed unless they are dwarf varieties.
• Add a few handfuls of sand and gravel to ensure good drainage around roots. In heavy soil, choose planting on a mound or within a rockery.
• Apply a dose of crushed horn if soil is sandy.
• Place plant in planting hole.
• Replace soil and firm lightly.
• Water.

Care

Despite their robustness in often very harsh climates, these trees are easily stressed by drought or pollution and can be fragile, susceptible to red spider mites such as Picea glauca Albertiana Conica, for example: avoid planting near a light-coloured wall, which causes needle drop. It is important to place spruce in cool conditions and to mist young plants with a jet of water in the evening during a heatwave.

Squirrels and rabbits sometimes cause severe damage to trunks of young spruce. Rust and pineapple gall caused by adelgids are fairly common attacks but not very damaging to trees.

Spruce should not be pruned.

Cones of Picea glauca

Multiplication

Simplest propagation is by sowing spruce seeds, which keep for a very long time when stored dry at low temperature. Cultivars are obtained by graft or propagation by cuttings in May–June.

Propagation by cuttings

• Prepare a pot deep by filling it with potting compost mixed with sand.
• Remove tips of August-ripened lateral shoots by pulling on them to obtain a heel.
• Remove needles located near base of the cutting.
• Insert them up to two-thirds of their length, ensuring they do not touch.
• Firm down, water then place them in a warm, humid, covered environment.
• In autumn, separate rooted cuttings and pot them into deep pots.
• Plant out young plants the following autumn in open ground.

Sowing

• Sow seeds as they are or after a period of cold, moist stratification in a sandy mix. Germination is generally rapid.
• Keep conditions cool.
• Prick out young spruce plants in September.

Uses and associations

Plant original specimens of medium to large growth as solitary specimens on a short grass meadow or on a large rockery such as Picea abies ‘Inversa’ with an entirely trailing habit which, without staking, spreads over the ground. Place Picea breweriana prominently facing a mountain chalet, for example. It will be marvellous with its branches bearing non-prickly needles that form graceful trailing draperies 10 to 15 m high. The bluish colouring of Colorado spruces (Picea pungens Jeddeloh, Glauca Globosa or Koster) or of the Arizona blue spruce (Picea engelmanii Glauca) is of rare intensity; species to plant in full sun in any soil and fairly tolerant of drought.

An idea for a combination: Pinus mugo ‘Ophir’ and Picea pungens ‘Glauca Globosa’ on a patchwork of heathers (Erica darleyensis ‘Ghost Hills’ for example) and fescues (Festuca glauca)

Dwarf specimens such as Picea abies ‘Nidiformis’ which forms a true stork’s nest with very bright apple-green young shoots, are excellent in rockery or in containers combined with other dwarf conifers, heathers, rhododendrons or Japanese azaleas. Forms with glaucous, silvery foliage such as Picea glauca, Picea pungens bring a sunny touch that contrasts with the dark greens of Picea orientalis, for example. The white dwarf spruce ‘Daisy’s White’ will brighten the scene with its platinum-blond shoots in spring which you can combine with the red shoots of a Photinia fraseri ‘Little Red Robin’ or the purple shoots of a Pittosporum tenuifolium ‘Purpureum’.

In a contemporary garden with geometric lines and masonry features, plant small specimens with slow growth to establish permanence, reinforce the garden’s graphic structure and diffuse its resinous essential oils. You can do the same on a stream bank where the rocks help highlight the fine textures of spruce branches.

In a zen garden spirit, pair Hondo spruce (Picea jezoensis var. hondoensis) with deciduous or evergreen species native to Japan such as Japanese maples, Japanese cherries, bamboos, nandinas, aucuba…

Did you know?

Picea omorika, Serbian and Bosnian spruce, is a rare species listed on the Red List of endangered species. It is recognised by its very columnar silhouette, whose upper branches rise and form a curious tuft in the crown, a very majestic specimen with dark violet cones that suits large gardens.

Sitka spruce, widely planted in Irish sphagnum heathland, contaminates salmon streams downstream because of decomposition of its acidic needles mixed with turf.