Needle juniper

Identification and origin

Juniperus rigida belongs to the cypress family, Cupressaceae. It is native to Japan, where it grows on Honshū, northern Shikoku, and Kyūshū, as well as Korea, northern and north-central China, Inner Mongolia, Manchuria, and the Russian Far East, where it is rare. It grows in dry, rocky places: arid mountain slopes in China, limestone outcrops and sandy shores in Russia. It has become locally naturalized in the United States.

It is an evergreen conifer that is almost always dioecious: male and female cones usually form on separate plants. It grows as a shrub or a small single-trunked tree with an open habit, its branches rising or spreading horizontally while the branchlets droop with age. It reaches up to 33 ft tall, with a trunk at most 18 in across. The thin, scaly bark is red-brown on young plants, then turns gray, fibrous, and shallowly fissured on old trees.

The needles are the best way to identify it. Borne in whorls of three, stiff and very sharp, they are usually 0–1 in long and 0 in wide. The underside is deep green; the grooved upper side carries a narrow white band of stomata. The round seed cones measure 0–0 in: green at first, they ripen to brownish blue or bluish black under a waxy bloom and give off a strong resinous scent. Each holds two or three seeds and takes two to three years to mature. The yellowish-green pollen cones are no more than 0–0 in long.

In Japan it has long been planted around temples and in gardens for its bright foliage and weeping habit. Its Japanese names, nezumi-sashi (“rat stabber”) and nezu, recall that its needles were once used to keep rats away. As bonsai, under the name toshō, it is famous for twisting trunks and bleached deadwood, and some collection trees are several centuries old. It attracts birds and is resistant to deer.

Light

Needle juniper wants full sun. Choose a very bright, open, well-ventilated spot. Too little light makes the inner foliage die back and invites pests, especially when the canopy is too dense. It handles hot, dry sites well. It is not a houseplant: grown in a container, it stays outdoors all year.

Watering

In the ground it tolerates hot, dry conditions well; it is mainly container plants that need close attention to watering.

In a pot, the roots fear excess water above all, because they need air. Let the mix dry slightly at the surface between waterings, but never let the root ball dry out completely. Then water thoroughly, until water runs from the drainage holes. Go by the feel and weight of the pot rather than a calendar: in hot, windy weather the pot dries much faster than under cloudy skies. Misting the foliage, especially after repotting, raises the humidity around the plant.

Potting mix

In the ground it needs well-drained soil, like the dry, rocky places where it grows in the wild; soil of average quality is enough. In a container, choose a very fast-draining mix, such as a standard bonsai mix or one that drains even more freely: water should run through at once and air should reach the roots.

Temperature

This is a very cold-hardy conifer, tolerating cold on the order of -20–-9 °F in the ground. The roots of a container plant are far more exposed: protect the root ball once temperatures drop below 14 °F, in a cold frame, an unheated greenhouse, or against a sheltered wall. In winter the foliage often turns purplish brown from frost; this is a normal response, and it greens up again in spring. It handles summer heat well.

Repotting

A container plant is repotted about every two years in early spring, as growth resumes; needle junipers are usually repotted a little later than scale-leaved junipers. Very old plants can wait longer. Do not prune the roots aggressively: remove only overly long roots and part of the old mix. Afterward, keep the plant in a stable spot, protected from extreme weather, and mist the foliage regularly.

Pruning

It tolerates hard pruning but never regrows from bare wood, so every branch you want to keep must retain some foliage. During the growing season, use sharp scissors to shorten long shoots that stick out of the silhouette, and thin overly dense foliage clumps at their base. Do not shear it like a hedge by removing every tip: this weakens the plant and turns the needles brown. An open canopy that lets in air and light limits inner dieback. After hard pruning, heavy bending, or overwatering, juvenile needles can reappear and persist for several years.

Propagation

It is propagated from seed or cuttings. Seeds are collected from fully ripe cones, which takes two to three years. Nurseries also offer young plants in all sizes, and specialist bonsai dealers sell everything from young plants to finished trees.

Common problems

A well-placed, well-grown plant resists pests well. A canopy that is too dense or a lack of light, however, favors spider mites, juniper scale, aphids, juniper needle miners, and webworms; check the foliage regularly, including in winter. Suitable treatments work, but also correct the underlying cause.

Rust is the most serious disease of junipers: swellings burst into brown galls that release orange, jelly-like spore tendrils. The fungus alternates with pear, hawthorn, and crabapple. It cannot be cured, and infected branches usually die. Burn them or put them in the trash, never in the compost. Japanese junipers are rarely affected.

Persistent browning usually points to a watering, drainage, or light problem rather than natural aging. As always, a symptom can have several causes: look at all the growing conditions before drawing conclusions.

Toxicity

Needle juniper does not appear among the toxic plants listed by veterinary references for dogs and cats: no toxicity is reported. Its needles are very sharp, however, so wear gloves when pruning or handling it.