Chinese juniper bonsai

Placement

Chinese juniper is an outdoor tree in every season. Give it full light all year in a sunny spot. It cannot live indoors for long; you can bring it inside for a day or two for display, then it must go back out. In midsummer, if the pot is shallow, shield it from the harshest hours of sun.

In winter it stays outside to go through its dormancy, but in a pot its roots freeze far sooner than in the ground. Protect them when temperatures drop below about 14 °F, for example in a cold frame, and keep it out of prolonged frost. The foliage sometimes turns purplish-brown in cold weather: it greens up again in spring.

Soil mix

Juniper roots are very fine: they need an airy, very free-draining mix with small particles. Equal parts akadama and kiryu work well; a basic bonsai mix of equal parts akadama, pumice and lava rock also works, with a little more lava rock in humid climates. A little charcoal in the mix helps soften the effect of hard water.

Watering

Water by observation: let the surface dry slightly, then water thoroughly until it runs out of the drainage holes. Chinese juniper tolerates some drought, better than needle juniper, but the root ball should stay slightly moist all year and never dry out completely. Above all, avoid overwatering. Regular misting of the foliage does it good, especially after repotting.

Fertilizer: during the growing season, organic pellets once a month or a liquid fertilizer once a week. In spring, a higher-nitrogen formula boosts growth; do not feed a freshly repotted tree.

Pruning

Foliage is what powers a juniper: never remove too much growth at once. It does not regrow from bare wood, so always leave foliage on every branch you want to keep.

During the growing season, use fine, sharp scissors to cut back to their base the long shoots that stick out of the silhouette. Let a shoot extend a little first, and only shorten the most vigorous one if enough green shoots remain. Never shear it like a hedge: removing all the growing tips weakens it and turns the foliage brown. If prickly juvenile needles reappear, the pruning has been too hard.

Thin overly dense foliage pads from the base: light and air must reach the interior, otherwise the inner foliage dies and pests move in. A healthy tree handles heavy structural pruning well, as long as every branch keeps some foliage.

Deadwood is one of the juniper’s signatures: jin on branches, shari along the trunk. The live veins that fed a dead branch dry out and weather into silvery-white wood that evokes the tree’s struggle against a harsh setting, as on the “Omiya” tree, a Chinese juniper around two hundred and fifty years old kept in the British national bonsai collection.

Wiring

Wire from fall through late winter. In spring the sap flows strongly and the bark comes loose easily: avoid that season. Young branches bend very well and the species accepts strong curves; protect thick branches with damp raffia or tape before bending them. Copper suits conifers; aluminum is easier to handle when you are starting out.

Choose wire about one-third the thickness of the branch, wound at roughly 45°, and wire the whole tree before bending. After thinning, fan the foliage pads out so every twig gets light: the tree should not look like broccoli. Be careful with deadwood, which snaps; on a large old branch, the deadwood can be split so the more flexible live part can be bent. Remove the wire before it bites in, cutting it at each turn. Branches too stiff to bend can be lowered with a guy wire. Do not wire a weak or freshly repotted tree.

Repotting

Repot about every two years in early spring, less often for an old tree. Slide the tree out of its pot: if roots are circling the root ball, it is time; if not, check again next year. Comb out the roots with a chopstick, removing no more than about a third of the fine roots, and set the tree in fresh soil. Afterward, keep it out of wind, scorching sun and frost, and mist the foliage.

Styles: juniper lends itself to dramatic twisted forms, the slanting style with deadwood, cascade, multi-trunk and forest plantings. Propagation: cuttings of the previous year’s wood in spring, with rooting hormone; seed; air layering in early spring, sometimes waiting two seasons before separating the layer. Air layering can also improve ordinary nursery stock.

Pests and diseases: a healthy tree in a good spot resists well. Watch, even in winter, for spider mites, juniper scale, juniper aphids, needle miners and webworms. Rust is the most serious threat: it forms galls on the juniper and alternates with pears, hawthorns and crabapples. It cannot be cured and an infected bonsai often declines; do not compost an infected tree. Blue-green junipers resist it better than yellowish-green ones.