Junipers are among the most popular bonsai trees. Eric loves working with them, and thinks they are a great choice for bonsai enthusiasts as well as anyone new to bonsai. The best way to learn how to style bonsai plants in general is to spend time looking at those plants where they grow in their natural environment. As a bonsai artist, Eric spends time in the mountains so he can see Juniper trees in nature.
Junipers are one of the most amazing genus of trees and shrubs in the world. They are evergreen coniferous trees with needle-like foliage. Wild Junipers are among the most contorted and wild of all tree species. The most interesting examples of wild junipers typically have a lot of deadwood, a lot of twists, and a lot of movement. This is what makes them such a great subject and a great inspiration for bonsai.
Numerous lessons can be taken from the natural forms of junipers. One of the key tenets of the art of bonsai is a reverence for nature. Thus the form of a bonsai typically imitates or is a caricature of the form of a natural tree.
Types of Juniper Trees
There are many types of Junipers, including Japanese Shimpaku Juniper, Chinese Juniper (Juniperus chinensis), Common Juniper (Juniperus communis), California Juniper (Juniperus californica), Rocky Mountain Juniper (Juniperus scopulorum), Utah Juniper (Juniperus osteosperma) and Sierra Juniper (Juniperus grandis).
Sierra Junipers in the wild are a particularly good example for bonsai design purposes as they form really interesting shapes across different locations. While Sierra junipers typically grow on good growing sites as straight-trunked upright trees with gnarled and short branches, when they’re forced to grow slowly, usually due to a lack of root space or consistently cold and windy conditions, they typically take on more interesting shapes.
California, Rocky Mountain, and Utah Junipers offer good lessons for designing a juniper bonsai. California junipers grow primarily in the desert mountains of Southern California. They are somewhat less grand looking than Sierra Junipers in that they tend to look like bushes across most of their range. Only in harsher (wind/snow) locations do they begin to resemble what people think of as bonsai.
Utah and Rocky Mountain Junipers are similar and combined they cover scattered patches across much of the western United States. In locations where there is little environmental challenge for them they become first large bushes and then small trees. In more difficult conditions they may remain quite small and look like naturally stunted bonsai forms.
Juniper Bonsai Health Issues
The most common causes of health problems with juniper bonsai are pinching, slow growth, pests and disease, fungal problems, and watering.
Pinching: anything that removes tips, or green foliage, but not brown branching at the same time. Cutting the strong tips off of a juniper impedes its ability to grow. Kishu and Itoigawa should only be pinched when they have a full mature canopy, and then only the runners are pinched annually around May. Pinching can also happen due to caterpillar damage or other insect damage, so keep an eye out for anything munching on new growth.
Slow growth: Junipers are slow growing and opportunistic growers. They’re largely native to harsh environments; they eek out an existence and grow when they get the opportunity. Slow growth does not mean the tree is unhealthy!
Pests, diseases etc: The two most common pests on junipers are juniper needle scale and spider mites.
Needle scale: Understanding the life cycle of needle scale is key to controlling it. The insect starts as an egg underneath a waxy white bump that is typically on the underside of shaded growth on the plant, but can be anywhere when there is a heavier infestation. To interrupt needle scale, try two things. First, spray a horticultural soap or oil once per week on an infested plant between late April and the end of May. Second, don’t allow the tree to become overly dense, or allow it to grow in a shaded location.
Spider mites: Spider mites are a very large problem for bonsai growers in hot areas. The mites are smaller than the tip of a pin, too small to see with the naked eye as anything but a small dot on a piece of paper. The first sign of mites is usually discoloration in the foliage of the juniper, from a nice rich green first to a pale or mottled green and then browning out eventually. This happens in patches, or branch by branch, not typically to the whole tree at once. Mites have become increasingly resistant to chemical insect control so the best primary control is to water the tree overhead 1-2 times per week, essentially giving the tree a wash down with a gentle hose. Spider mites are blown in by wind, but they don’t cling to the tree particularly well so they can be dislodged by even a gentle tap or stream of water.
Fungal problems: Junipers thankfully are not particularly susceptible to fungal problems, but they can get tip blight. Tip blight shows up as blackened tips on the tree, and seems to be more prevalent in wetter or shadier conditions. Keep trees healthy, plant them in free draining mix, and fertilize regularly as a healthy plant will be more able to respond to an infestation than a weak one. Spray with neem (which is both a fungicide and insecticide) or another preferred fungicide. The key to fungal control is regular application to disrupt the cycle of the fungus.
Watering: Too little or excess water are among the most common causes of death for bonsai, including junipers. How much water do Juniper bonsai need? It’s not about having enough water, it’s about learning how much water your tree can absorb during any given watering. The soil surface alone shouldn’t be wet; the water needs to soak in for the tree to absorb. Take time before a vacation to set-up a regular watering system and a back-up (trusted friend or family member who understands proper care for your bonsai plant!)
Junipers really are outdoor plants; they grow quickly in hot weather, and slowly in cold weather. Temperature is one of the most influential factors in the speed of growth. The other factors that affect the metabolic rate are:
Availability of nutrients: e.g. food and good water. For more information about organic fertilizers, watch this video and for mineral (sometimes liquid fertilizer), watch this video.
Ideal root conditions: primarily facilitates water and nutrient uptake.
Many hours of direct sunlight: the primary source of energy, so go full sun whenever you can!
Good Air Circulation: provides optimal oxygen and carbon dioxide.
High Humidity: keeping humidity levels higher allows for higher temperature without water stress. Water stress can cause the stomata to close, slowing metabolic functions.
Roadmap for Juniper Bonsai Care
To ensure healthy growth and development of Juniper, different work needs to be done on a regular basis at different times of year. Below is a basic roadmap for when to best work on the plants so that they respond well and continue to grow afterward. If work is done out of season the plant will either suffer damage or the metabolism will slow down.
Spring: in the early spring the flush of new growth causes a surge in wood production that can be seen in cross sections of the plant as the lighter colored portion of the annual ring. The wood is less dense than the wood produced later in the year. At the same time, the cambium is actively dividing itself and creating additional layers of bark. During this period the cambium is easily separated mechanically from the wood underneath. You can use this to your advantage if you are creating jin or shari. But, overall caution is needed when doing any wiring or bending on junipers during the spring growing season. It’s actually best to wait until mid-summer to wire them, leaving the spring months for growth, or light thinning only.
Summer: Growth can be fast in the summer months, but the wood production is slower. I generally start working on junipers in late summer, July and August. Plan to work on junipers in summer if there is enough growth to work with or if they need to be thinned to prevent shading of lower branches.
Fall / Winter: Fall and Winter are the ideal seasons to bend and work on junipers. While the plant is in a dormant period the cambium is solidly attached so the branches are less likely to be mechanically damaged during styling. Cleaning up foliage and bending is done at this time.
Winter / Early Spring: the best time to repot is through the winter months or into early spring, ideally before the new tips are growing vigorously. Late winter and early spring seems to be the ideal time for the best results. Repot the tree into a good bonsai soil mixture; provide as much sunlight, heat, humidity and good air circulation as possible. As a general rule, protect freshly repotted trees to ensure that the tender roots aren’t damaged by hard frost or freezing that can occur during a cold snap.
Want Eric’s advice on keeping Juniper bonsai indoors or outdoors? Don’t keep them indoors! Many people struggle to grow Juniper bonsai (Juniperus procumbens ‘nana’) indoors because they missed the memo that this tree is not like typical indoor plants, but needs to be outside! It’s a temperate-climate plant, and grows best in full sun with lots of air movement. If you want to keep a Juniper inside, do so only for short periods of time and get creative to see what conditions you can create to make them grow and thrive! Perhaps try placing it on a humidity tray or set it underneath a grow light. No matter how many hours of sunlight the tree gets while indoors, it’s not a good idea to keep Junipers inside. While Junipers do not make good indoor bonsai, they sure are an excellent choice to have as part of your bonsai collection!
