Spruce - Picea sp.

General information: 35 species of this evergreen are widely available in the US. Many varieties are tall, conical to pyramidal trees, most familiar as a popular Christmas tree. Some species tend towards globular growth, and slow-growing spruces can be used as shrubs. Spruce has scaling or flaking bark, and, in general, its needles are short enough for use in most sizes of bonsai, with many dwarf varieties available.

Due to the branch formation in whorls and natural tendancy of some spruce species towards pyramidal growth, the spruce can be a difficult bonsai subject. It enjoys popularity, however, because it makes a stately bonsai when properly styled, and material is readily available.

Needlelike leaves are persistent for several seasons, but much shorter than those of pine; born singly and closely in spirals; four-sided or diamond-shaped in cross section. Each leaf appears narrow at the base. Flowers appear as small cones, male and female on the same tree. Spruce have a pendent woody cone with thin, smooth or ragged-edged scales.

Lighting: Full sun, but needs shade from the midday sun in summer, or needle browning will result.

Temperature: These northern trees prefer cool temperatures, although small or young bonsai may need frost protection. Many species are hardy to zone 3 or colder, although there are some which grow well only as far north as zone 6.Picea glauca 'Conica' is capable of withstanding heat and drought better than other spruce bonsai. In general, spruces like wind and need good ventilation.

Watering: Spruces prefer moisture, but not waterlogged soil. Reduce watering in winter, but never allow the soil to dry out completely. Misting is appreciated spring-fall.

Feeding: Every two weeks, spring-midautumn, using liquid bonsai food or half-strength general purpose fertilizer. In hot areas, discontinue feeding during the heat of summer. Apply a chelated iron supplement several times yearly.

Pruning and wiring: Popular both as single specimen trees and when grown in forest plantings - 'Little Gem' spruce is especially popular for Saikei. Jin and shari look especially nice on spruce bonsai. When purchasing spruce for bonsai purposes, be careful to avoid grafted trees as these will form unsightly bulges at the base. Suitable for all styles except broom, and for all sizes, with small sizes best reserved for dwarf varieties. New growth should be pinched, not clipped, several times in spring, when shoots are about 1 inch long, leaving 4-5 clusters of needles. Do major pruning in early fall. Never remove all needles. Wire between late autumn and winter. Picea glauca 'Conica'is a slow-growing specimen. To encourage compact, dense growth on it, pinch out the apical buds as they emerge and cut back long shoots. It does not set as well when wired as other trees. It is often necessary to exaggerate the bend desired when wiring to end up with proper branch placement.

Propagation: Seeds need cold pre-treatment, and are generally sown in winter or early spring. Seeds may be collected from cones between September and January, late August-September for P. glauca. Remove seeds as soon as they appear at the edge of the scales, but allow them to mature in the cones as long as possible. Softwood cuttings may be taken in late autumn or early spring, but rooting is tricky and may take up to two years.

Repotting: In general, epot every second year in early to mid-spring, before new growth expands, or in early fall. Older specimens (+10 years) may be repotted every 5 years. P. Abies may only need repotting every 3-4 years. Use fast-draining soil mix, and prune roots by 1/3 or less. Spruce, in general, need to keep a decent-sized root ball, and may need to be planted in a deep pot to achieve this. Protect from full sun for a few weeks after repotting. P. jezoensis should be allowed to rest for 3 months after transplanting before wiring. Picea engelmannii is one of the toughest spruces, and is forgiving of mistakes made due to over-enthusiastic root/branch pruning.

Pests and diseases: Mites are the worst problem, and in hot weather they can build to populations which require control. They can be a major problem in summer after hot dry weather, especially near concrete, buildings, and other urban surfaces which reflect heat. The small insects can't be readily seen with the naked eye. The first noticeable symptoms are yellowing at the base of the oldest needles on infested branches. Close inspection with a magnifying glass will confirm the presence of the mites.

Two gall-forming insects commonly attack Spruce. Eastern Spruce gall adelgid forms pineapple like galls at the base of twigs. Galls caused by Cooley's Spruce gall adelgid look like miniature cones at the branch tips. The gall adelgids do not kill trees unless the infestation is heavy. A few galls on a large tree are not serious.

In northern climates, Spruce budworm larvae feed on developing buds and young needles. The yellowish brown caterpillars are difficult to see.

The Spruce needle miner makes a small hole in the base of a needle then mines out the center. Dead needles are webbed together and can be found on infested twigs. Hand pick these from the tree to reduce future damage.

Diseases: Cytospora canker infects a branch then eventually kills it. The lower branches are attacked first then progressively higher branches. The needles turn brown to reddish brown and eventually drop off. White resin patches are seen on infected branches. Prune off infected branches. Water Spruces during dry weather.

Spruce may be attacked by needle casts. One causes needles to turn yellow or brown and drop off. Another affects the lowest needles first then moves up the tree. Infected needles are a mottled yellow.

Some species suitable for bonsai:

  • Picea abies: Norway spruce - With its red brown bark, conical shape, and shiny green needles, Norway spruce is traditionally used as a Christmas tree. Its needles are 3/4 inch long, and it grows to 90 feet in nature. It survives at high altitudes, up to 6600 ft.
  • Picea abies albertiana 'conica'.
  • Picea abies 'Echiniformis': dwarf spruce - a slow-growing form with tightly congested foliage.
  • Picea abies 'Little Gem': dwarf spruce - an excellent variety for use in Saikei due to its tiny needles and small, compact growth.
  • Picea abies 'Maxwellii': Norway spruce, dwarf spruce - This is a natural dwarf. It has coarse, spiny needles.
  • Picea abies 'Mucronata': dwarf spruce.
  • Picea abies 'Nidiformis': bird's nest spruce - This dwarf has bright, fresh green buds and grows to 3 ft.
  • Picea abies 'Pumila' - This variety has small, dense foliage which makes it desirable for bonsai culture. It grows very slowly - as little as 1 foot in a 25 year period.
  • Picea abies 'Pumila Nigra' - small, deep green foliage, with light green buds in spring. Takes well to pot culture in hot, humid areas. Very similar to the hard-to-find P. glehnii.
  • Picea abies 'Pygmaea': pygmy Norway spruce.
  • Picea abies 'Verigata': white spruce.

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