Norway spruce bonsai

Placement

Picea abies is a conifer of Europe’s forests and mountains, grown outdoors all year. During the growing season it needs full sun, with light shade during the hottest part of summer days: the species prefers cool summers and suffers in heat. It handles wind well and appreciates good air movement.

In the ground it is one of the hardiest trees, but in a pot its roots are exposed. A spruce bonsai tolerates about 14 °F; below that, protect the pot. Cold is not the only danger: frozen roots can no longer supply water while the evergreen needles keep transpiring, and the tree dries out. In winter, place it in partial shade, out of the wind; where temperatures often fall below 14 °F, a cold frame or cold greenhouse is safest. Failing that, wrap the pot in insulation or bury it up to the level of the roots.

Soil mix

Spruce is not fussy about the pH of the mix or the water, but it needs a very free-draining mix with stable grains that do not compact. A common mix for conifers combines equal parts akadama, pumice, and lava rock; sift the akadama to remove the dust. In a wet climate, raise the share of lava rock or grit; if you cannot check on watering often, raise the share of akadama.

Watering

Water thoroughly as soon as the mix starts to dry, then let the excess drain away: the roots should not stay soaking wet. In hot summer weather, a small pot can dry out very quickly; in winter, the dormant tree drinks much less. Watch and feel the mix rather than following a schedule. In winter, water less, but never let the root ball dry out completely.

Fertilizer: during the growing season, apply a solid organic fertilizer every four weeks or a liquid fertilizer every week; feeding every two weeks also works. A foliar spray of liquid fertilizer containing chelated iron gives the needles a deeper green.

Pruning

Spruce is a tricky species to style, for two reasons. Its branches grow in whorls, several at the same height, which creates unsightly swellings and a trunk with poor taper: in the lower half of the tree, keep only one branch per whorl. Above all, it almost never buds back on old wood: a bare branch that has turned completely brown and lost all its needles will not regrow. Always leave needles and buds on any branch you want to keep.

In spring, pinch new shoots while they are still soft, once they reach 1–1 in, leaving four or five groups of needles. To shorten an overlong branch, cut back to a smaller twig closer to the trunk. Save hard pruning for fall, to limit resin bleeding.

Spruce suits every style except broom, and every size, from small trees to large specimens.

Wiring

Spruce branches are very supple and bend without snapping, but they take a long time to hold their new position, often several years, so rewiring is usually needed. Wire outside the growing period, from late summer through winter; wiring in spring or summer, and especially in midsummer, can make branches die back.

Copper wire, which is harder, suits conifers well; aluminum, easier to handle, can also be used. Choose wire about one third the thickness of the branch, wound at roughly 45° and anchored with one or two turns around the trunk. Wire every branch you plan to move before bending, and protect thick branches with wet raffia. Check the wire regularly during growth and remove it before it marks the bark, cutting it at every turn rather than unwinding it.

Repotting

Repot every two to four years, less often for a very old tree. Spruce often sulks after a spring repotting: late summer or early fall, once the buds on the new growth have formed, is a very reliable time. Prune the roots lightly, because older trees cope badly with losing large roots, and never remove more than half of the old mix at once. Replant in a free-draining mix, water thoroughly, and keep the tree out of full sun while it settles in.

Propagation: sow seed outdoors in spring. Cuttings are taken in late summer from ripened wood, but they can take a very long time to root.

Pests and diseases: aphids, including the green spruce aphid, and spider mites are the most common; adelgids, which cause galls, needle miners, budworms, and other caterpillars can also attack. As for diseases, watch for rust and the fungi that make needles drop. Treat with a targeted product and, for a severe attack, ask a professional for advice. The same symptom can have several causes: browning can also come from a root ball that has dried out or from frozen roots.