Japanese white pine bonsai

Placement

Japanese white pine is grown outdoors all year, in full sun. It handles long hours of sunshine, and that light is what keeps its needles short and dense: long, limp needles mean it is not getting enough sun. Indoors the light is too weak and the air too unchanging: the tree weakens quickly and eventually fails.

This high-mountain pine needs a real winter rest. Several weeks between 32 °F and 45 °F let it preserve its reserves; in a climate that is too mild it exhausts them within three to five years and loses buds, then branches. It is also very cold hardy: a tree in the ground withstands severe frost below -4 °F. In a pot, it is the roots that fear the cold. A container at least 12 in wide copes well with temperatures below 19 °F; where winter drops below 14 °F, place the tree in a cold frame, which evens out temperature swings and prevents drying winds, or wrap the pot in insulation, or bury it in the garden up to the roots. Above all, do not bring it into the house.

It also tolerates heat, even above 100 °F, but because it moves water slowly, a shade cloth of about 30 % protects it during heat waves.

Soil mix

This pine draws a lot of oxygen from the soil, so the mix must be very free draining and airy. Equal parts pumice, lava rock and akadama work well. Sift it to keep only particles of about 0–0 in: finer particles hold water and push out the air. The pot must drain immediately.

Watering

It is one of the bonsai that need the least water, because its roots need as much air as moisture. Each time you water, soak the whole root ball until water runs from the holes, then let the mix dry out thoroughly before watering again. Check the surface and the weight of the pot instead of following a calendar: in hot weather it can dry in a day or two, in winter much more slowly. Overwatering is one of the main causes of decline: suffocated roots, yellowing needles, weak shoots. In spring, shelter the tree from long spells of rain while the shoots are growing, since too much water at that stage lengthens the needles.

It is very sensitive to water quality. Hard water or water with a high pH yellows the foliage; use clean, slightly acidic water such as rainwater.

Fertilizer: feed from early spring to late fall with an organic bonsai fertilizer, avoiding nitrogen-rich products. A weakened tree can be fed all year as long as it is not too cold.

Pruning

Japanese white pine produces only one flush of shoots a year. Never remove all of its candles, a technique reserved for two-flush pines such as black pine: it could kill the tree. From late spring to early summer, instead shorten overly long candles to an even length, pinching them by hand rather than with scissors, which turn the needles brown. Where more than two candles grow from the same point, keep two.

Branch pruning is best done once the new shoots have hardened, when the dry sheaths that protected the young needles have fallen; the tree then starts rebuilding its reserves. Early fall is the second good window. At that time, remove surplus shoots: at each point, keep two lateral shoots of equal strength, heading in the desired direction and forming a V. On vigorous areas, pluck some of the old needles to balance growth. Reducing the foliage by half is safe; beyond that, watch watering closely. Save major structural pruning for late winter and avoid heavy pruning in late summer.

Leave the flowers in place: their appearance is not a sign of poor health.

Wiring

Wire from early fall to early spring, or right after shortening the candles in early summer. Copper wire, which is stiffer, suits pines well; choose the thinnest wire that will hold the branch, roughly one third of its thickness, wound at about 45°. On thick branches, protect the bark with damp raffia. Check often: the branch can grow over the wire within a few months. Remove it by cutting at every turn. Never wire a tree that has just been repotted.

This pine can be shaped in almost every style, including the literati style (bunjin). Its bark stays smooth and gray for a long time: on average it takes about thirty years to look mature.

Repotting

Repot about every two years for a young tree and every three to five years for an established one, in spring, before or just as the buds begin to swell. Repotting is also possible in late summer or early fall, once the heat has passed but while there is still time to grow new fine roots before winter. Keep at least half of the root mass intact: it holds mycorrhizae, fungi associated with the roots that pines depend on.

Japanese white pine is mainly propagated from seed; cultivars with desirable needles, such as ‘Zuisho’, ‘Kokonoe’ or ‘Myojo’, are often grafted onto Japanese black pine rootstock for steadier growth, and ‘Zuisho’ can be grown from cuttings. It resists disease well; the main pest is the woolly adelgid, which attacks candles and buds in spring: a suitable oil or predatory insects deal with it. Aphids, spider mites, scale, caterpillars and root rot are still possible. If the tree declines with no visible cause, check the roots first.