Juniper trees are an especially popular choice for bonsai due to their easy care requirements and attractive foliage. Native to Europe, Asia, and North America, junipers have a naturally compact growth habit which makes them well-suited to bonsai growing techniques. They have evergreen, needle-like foliage that ranges from dark green to steely blue. Most juniper varietals will grow at a steady pace, adding between 6 and 12 inches of height per year. Because some juniper species are low-lying ground cover shrubs, they also make fantastic cascading bonsai due to their natural downward growth habit. As with most species chosen for bonsai, juniper trees take well to wiring, although it should be done slowly and carefully. Wiring is the practice of wrapping a wire around the branches of the bonsai tree in order to bend and reposition the branches to achieve the desired shape. It is best to wire a juniper bonsai during the winter months when the tree is dormant. Once the branches have set in their new shape, carefully remove the wire with wire cutters so you don’t damage the tree. There are two main categories of juniper trees—trees with scale-like foliage and trees with needle-like foliage. Identifying which type of juniper bonsai you have will help to determine how to care for it properly. Juniper trees with scale-like foliage include the Chinese juniper and the California juniper, while juniper trees with needle-like foliage include the Japanese needle juniper, green mound juniper, and the common juniper.
Light
Juniper bonsai require bright, direct sunlight, at least six to eight hours of full sunlight daily. For this reason, most species of juniper bonsai are best-suited to being grown outdoors year-round.
Soil
Use a commercially available bonsai soil mix for juniper trees for the best results. Bonsai soil mixes are well-draining—allowing both air and water to reach the roots—and are typically a combination of akadama (clay granulate from Japan), organic potting compost, pumice, and fine gravel or grit. They can be found at most garden centers or plant stores, or online from specialty bonsai retailers.
Water
As with most bonsai, juniper bonsai require regular watering to keep the soil consistently moist. However, they cannot tolerate being waterlogged. As a general rule, allow the soil to dry slightly between waterings (but avoid letting it dry out completely), then water deeply. Additionally, ensuring that the bonsai has adequate drainage is imperative to prevent the soil from becoming waterlogged.
Temperature and Humidity
Juniper bonsai trees should be grown outdoors year-round and cannot tolerate growing indoors. They are hardy, frost-tolerant trees that can withstand temperatures as low as 10 degrees Fahrenheit without protection. When extreme winter temperatures dip below that temperature, provide your juniper bonsais with moderate protection from wind and frost to help them overwinter outdoors.
Fertilizer
Juniper bonsai appreciate regular feeding during the growing season to promote strong growth. However, do not fertilize them during the winter months. Use slow-release organic fertilizer once a month during the growing season, or a liquid fertilizer every week when watering. If vigorous growth is desired, a nitrogen-rich fertilizer is recommended—but only in the spring months. To avoid shocking the roots, don’t fertilize a juniper bonsai for at least a month after it has been repotted.
Types of Juniper for Bonsai
The Juniperus genus contains between 50-70 species of trees and low-lying shrubs. The most popular juniper varieties for bonsai include:
Chinese juniper (Juniperus chinensis): Also known as Hollywood juniper, this species has scale-like leaves and creates a twisting form as it matures. Common juniper (Juniperus communis): Found throughout the world, this varietal has needle-like leaves and is adaptable to many different locations, including especially windy sites. California juniper (Juniperus californica): Typically grown as a shrub, this juniper species is primarily found in the Southwest and is prominent in drought-tolerant gardening.
Pruning
Proper and regular pruning is essential to the aesthetic and health of a bonsai tree. For juniper bonsai, pinching back growth rather than cutting it back is recommended, as cutting can cause the surrounding needles to die off. Juniper trees can withstand aggressive pruning well but keep in mind that they cannot bud again from any bare tree parts. Always leave some foliage on the branches to ensure ongoing growth. It is best to prune juniper bonsai in the early spring and summer during their active growing period.
Propagating Juniper for Bonsai
Growing your plant collection through cuttings—also known as “Sashiki” in Japanese—is very common among bonsai enthusiasts, especially if they’ve found a varietal that takes very well to the shaping and grooming that bonsai requires. Juniper plants are also relatively easy to grow from cuttings, and propagating methods are best done in the late spring and summer months. Here’s how:
Potting and Repotting Juniper for Bonsai
In general, bonsai trees do not need to be repotted very often, including the juniper varieties. Young trees can be repotted every two years at the most, and older trees can go as long as five years without being repotted. For juniper bonsai, avoid heavy root pruning at the time of repotting to prevent shocking the plant. When choosing a vessel for your juniper bonsai, focus on those made of natural materials like clay or terracotta, which can help wick away excess moisture from the soil.
Common Pests & Plant Diseases
Juniper plants are not affected by a large number of pests, but they often have issues with one in particular: the spruce spider mite. Typically unable to be seen by the naked eye, the spruce spider mite will suck on the sap of the plant, which results in browning and dropping of the needles. A particularly heavy infestation can be recognized by fine webbing on the plant, but smaller populations of mites can go unnoticed if not for damage to the plant. To control the pest, periodically blast your plant with strong water. Insecticides can be used to kill large infestations. Juniper plants can also contend with various fungal diseases, like blight and rust, which are both characterized by the browning and dropping of branches and needles. Most of these issues are brought about due to improper planting, like locating your juniper in a spot that is shaded or poorly drained. If necessary, fungicides can protect your plant from these issues.
