Pruning

Pruning Japanese Juniper bonsai trees is a relatively easy process and is best done at two or three optimal times throughout the growing season.  First, in early Spring, allow your Juniper bonsai to grow freely and do not prune the new shoots as they emerge.  Allowing the growth to elongate will assist with growth hormone transport throughout the tree, producing more vigorous root growth and subsequent shoot growth.  Once the new shoots have fully elongated, typically by early summer, prune each shoot back using scissors.  Be sure to cut the shoot itself and not the foliage tips.

After the first pruning, Junipers will flush a second time.  Allow this secondary flush to elongate again for six to eight weeks, then prune again.  Repeat this process throughout the growing season as needed.  By pruning Japanese juniper bonsai in this way, you can easily create a full, well-developed bonsai in a short period of time.

Additionally, juniper bonsai will likely shed interior foliage as the temperatures start to heat up in summer.  This yellowing growth is referred to as toya in Japanese.  This is a normal process wherein the tree is shedding weaker foliage in favor of stronger external foliage to help offset over-transpiration.  In order to limit the amount of toya produced by a juniper bonsai, consider removing some growth from the tree earlier in the Spring season.  For example, remove foliage on the undersides of pads, as well as crotch growth and unnecessary branches in the tree's design.  Once again, though, be sure to leave the extending shoots intact and uncut at this point in Spring.

For a more in-depth look at pruning techniques, please consider joining our online bonsai learning platform Bonsai-U!

Wiring and Styling

Wiring and styling of Japanese juniper bonsai can be done at any time throughout the year.  However, keep in mind that the more invasive the work, the more you will want to avoid the hottest and coldest times of year to perform the work.

For example, if you plan to split branches, apply raffia and heavily bend branches into place, this work is best done in the fall.  If, on the other hand, you are simply detail wiring a juniper bonsai, this can be done at any time throughout the year, including mid-summer and deep winter.

Creating shari on junipers can also be done at any point during the year; however, the optimal time to perform this bonsai technique is in early to mid-summer.  At that time of year, juniper vascular tissue can be easily peeled and will immediately begin to callous along the edges of the newly created shari deadwood.  Avoid winter for this type of work if possible, as callous formation is non-existent when junipers are dormant.

Repotting

Repotting juniper bonsai is best done in early Spring just as the foliage begins to return to a normal green color.  This usually happens sometime in March in the northern hemisphere.  When repotting, do not remove all of the original soil, but rather leave a core of older soil beneath the trunk to preserve the health of the bonsai.  Avoid cutting too many roots as well, as this can often cause the juniper to revert to juvenile foliage in the subsequent growing season.  This is particularly true with Itoigawa Shimpaku.

Use a free-draining soil medium, such as Aoki Blend or a mixture of akadama, lava rock and pumice in a ratio of 1:1:1.  The soil particle size should be approximately 3/16 inch (4mm) for medium and large trees, and slightly small for shohin size bonsai.

Watering

Japanese juniper bonsai do well if kept slightly moist.  As a general guideline, check the water twice per day during the growing season from early Spring through late Fall.  Most juniper bonsai will need to be watered at least once per day, and sometimes twice per day, during this period.  Water as the soil surface becomes dry and mist the foliage when watering in the morning.  In the winter months, check once per day and water as needed, which could be as little as once every 3-5 days depending on the climate and the individual juniper bonsai.

Fertilization

Fertilizing Japanese juniper bonsai will be dependent on the stage of development of the tree.  For example, younger junipers are best fertilized with a high-nitrogen synthetic fertilizer to rapidly increase their size and vigor.  Older, more refined juniper bonsai should be fertilized with a milder organic fertilizer with a lower nitrogen value.  All junipers, regardless of development, should be fertilized from the early growing season through late Fall.

Placement

Place Japanese juniper bonsai in full sun year-round.  If you happen to live in a very hot, dry climate, though, consider placing them in afternoon shade.  At Eisei-en we place many of our juniper bonsai under 30% shade cloth during the hottest summer months.  You might notice that your junipers become slightly greener or bluer under shade cloth.  This is normal and can be quite dramatically beautiful.

Pests/Diseases

Japanese juniper bonsai are susceptible to a number of pests including aphids, bagworms, borers, scale and spider mites.  The most common diseases that affect junipers are tip blight and cedar-apple rust.  For a comprehensive understanding of what fungicides and pesticides to use on your juniper bonsai, please join Bonsai-U!