Norway spruce

Identification and origin

Picea abies belongs to the pine family, Pinaceae, along with pines, firs, and larches. Linnaeus first described it as Pinus abies. It is native to Europe: from Norway, Sweden, and Finland to the Baltic States and European Russia, and south to France, Switzerland, Germany, Poland, Austria, Italy, the Balkans, Greece, and Romania. It has naturalized in many regions, including Great Britain, Ireland, Denmark, the Netherlands, Spain, and the northeastern United States and eastern Canada; in North America it is the most widely planted spruce in horticulture.

It is a fast-growing evergreen conifer. Conical and upright when young, it develops a dense pyramidal habit with age, with drooping branches whose tips turn up. In gardens it usually reaches 39.5–59 ft tall and 24.5–29.5 ft wide.

The needles are dark green and glossy, stiff, four-sided, and saber-shaped, up to 1 in long. They are attached one by one all around the twig, like the bristles of a bottle brush, and stay on the tree for several years.

In spring, the yellowish-brown male cones grow in clusters; the purple female cones stand upright until wind pollination, then turn green and hang down. Ripe in fall, they are 4–6 in long and 1–2 in wide, with rounded scales; green to violet at first, they turn silvery brown. The black seeds carry a pale brown wing. The bark, thin and purplish, green, or silvery brown on young trees, thickens and becomes scaly with age.

Norway spruce is the traditional Christmas tree in Great Britain, has served several times as the U.S. Capitol Christmas tree, and is an important timber tree in Europe. Among its many cultivars:

• ‘Nidiformis’: dwarf, flat-topped cushion with a hollow center, 3.5–5 ft tall and 8–13 ft wide.
• ‘Pumila’: rounded dwarf, about 3–4 ft tall.
• ‘Acrocona’: small tree, 8–13 ft, with drooping branches and bright pink to red female cones in spring.
• ‘Pendula’: weeping form, about 12–15 ft.
• ‘Cupressina’: narrow, upright form.

Light

Norway spruce needs full sun, meaning at least six hours of direct light a day. It grows in any exposure and handles both a windswept open site and a sheltered one; it also tolerates urban air pollution.

Watering

It likes moderately moist soil and suffers from both summer drought and excess water: its root system is shallow and it does not tolerate wet feet. In the ground, water deeply during dry summers, when the soil is dry below the surface.

In a container, water thoroughly as soon as the mix starts to dry, then let the excess drain away; the roots should never sit in water. In winter, water less often but never let the root ball dry out completely: an evergreen conifer keeps losing water through its needles even when dormant.

Potting mix

It prefers moist but well-drained soil, ideally sandy and acidic, or neutral. It also grows in clay or loam as long as water does not stand. In a container, choose a free-draining mix with a stable structure that does not compact over time.

Temperature

It is one of the hardiest conifers: it is grown in USDA zones 2 through 7 and withstands the harshest continental winters, well below -4 °F. Heat is its real limit: it prefers cool summers, suffers in hot, dry summers, and performs poorly where summers are scorching. In a container, its roots are more exposed to freezing than those of a tree in the ground: in winter, shelter the pot from wind, bury it, or wrap it in insulation during hard freezes.

Repotting

For a dwarf spruce in a container, repot when the roots have filled the pot, usually every two to four years, and less often for an old specimen. Prune the roots sparingly: older trees cope badly with losing large roots, and it is best not to remove more than half of the old mix at once. Late summer or early fall, once the year’s buds have formed, is a safe time, because the tree often sulks after a spring repotting. Afterward, keep the pot out of full sun while it settles in.

Pruning

In the ground, Norway spruce needs no pruning: give it room to develop its shape. If you must cut, remember that it does not resprout from old wood: a branch cut back behind its needles will not grow back. Always cut above twigs or buds that carry foliage, and pinch young shoots in spring while they are still soft. Heavier pruning is best done in fall, when resin bleeding is lower.

Propagation

The species is propagated mainly from seed, sown outdoors in spring. Semi-hardwood cuttings can also be taken in late summer; they can take a very long time to root.

Common problems

It resists air pollution and deer, but several pests and diseases can affect it:

• Aphids and adelgids: green spruce aphid and adelgids, which cause galls on the twigs, are common.
• Mites: spruce spider mites attack the needles.
• Caterpillars and borers: budworms, needle miners, bagworms, wood borers, and weevils can attack the tree.
• Diseases: cytospora canker, rusts, needle cast, wood decay, and honey fungus.
• Branch completely brown and bare: it will not regrow; remove it.

The same symptom can have several causes: yellowing can come from excess water, drought, or too much heat as easily as from a pest. Check growing conditions before treating.

Toxicity

The reference lists of plants toxic to dogs and cats do not include Norway spruce, and no toxicity has been reported for this species. As with any plant, still keep pets from chewing on needles and twigs.