Wiring and Thinning Junipers

BY ARTIST DAVE PARIS

The juniper is one of the most common bonsai – but that hardly means it needs to be cookie cutter!  By understanding the mechanics of wiring &bending along with the horticultural requirements for thinning, most junipers will happily conform to nearly any plan.

As with most things, timing is everything.  Late April is usually a great time to start wiring and working on junipers.  If the spring has been on the warm side, you’ll probably notice new growth, too.  This is your prime clue that a juniper can start to be worked.  As with most evergreens, it’s still better to wait until landscape plants have leafed out to do your repotting although juniper tend to be more flexible about this than pines.  A downside to junipers is that it can appear to be quite healthy and green for up to a few months after it’s long dead.  This is due to the ability for the foliage to live off the little remaining sap in the branches.  Fortunately, they tend to be tolerant of a little neglect and abuse.

The two most common types of juniper are procumbens nana (dwarf Japanese garden juniper) and shimpaku.  Conveniently, these also represent the two types of foliage found on junipers;  needle leaf and scale leaf.  Needle leaf is considered to be juvenile while scale leaf is considered to be mature.  A stressed shimpaku will produce needle leaf foliage and then return back to scale leaf.  Conversely, a healthy procumbens will stay as needle leaf, occasionally putting out the odd scale leaf.  There is no concern when this happens.

Most styling of juniper is accomplished by wiring.  Since wire can be left on a juniper for up to 12 months, copper wire is most often used.  Aluminum wire can also be used, but due to the aggressiveness of some bends placed in junipers, copper holds the bend better than aluminum.  If you wire regularly, the need for major bending later will be reduced.  As branches become strong enough to be wired, shape them according to your design.  This reduces the chances of breaking a desirable branch later when it’s thicker and more brittle and/or rigid.  On the upside, just about any juniper branch (and occasionally the trunk) can be bent with appropriate mechanical techniques and patience. Wiring supplies can be found at www.hollowcreekbonsai.com

Two main wiring techniques are used on junipers;  coiling and guy wires.  Coiling is the more common method where a length of wire is wrapped around a branch at approximately 45deg to the branch, carefully avoiding new foliage.  A good guide to use for wire size choice is to use wire that’s approximately 1/4 to 1/3 the diameter of the branch when using copper wire and a wire that’s approximately 1/3 to 1/2 the diameter of the branch when using aluminum.  Be sure to have a bending plan so the wire appears on the outside of any bends you plan on making.  This will support the branch and reduce the risk of breaking it.  If your plan includes radical bends, additional measures will be needed.  This could be through the use of raffia wrapping and/or splitting the trunk or branch.  If the bend will be in a particularly thick branch, one or more wires can be placed parallel to the branch, sandwiched between layers of raffia, and applied so these wires are on the outside of bends.  This will give additional holding power and break resistance.  It’s not uncommon for guy wires to also be used to hold the bend in place on larger branches or trunks.  You’ll want some sort of mechanical device to assist in severe bends.  This could be a length of rebar, a branch bender, or a bonsai jack.  Of these three, the bonsai jack is the most controllable and can be helpful when creating a severe bend over the course of a day or two since it can be left in place with little supervision and no risk of slipping or moving.

Thinning and pruning juniper are two different operations and the methods differ between shimpaku and procumbens.  Too much pruning (more than roughly 40% of the foliage) on a shimpaku will stress it to the point of it producing juvenile foliage.  As the tree recovers, the familiar mature scale leaves will replace the juvenile needle leaves.  However, if we approach the pruning gradually, we can avoid the juvenile foliage appearance.

Most often, pruning is done to either shorten branches or to reduce heavily congested branch ends.  Through careful selection of branches to be pruned, an open yet well ramified network of branch tips is established.  Both pruning and thinning are carried out from spring to early fall, stopping in early September to allow the tree to store energy for the coming winter.

Pruning is done using shears or concave cutters.  It is not necessary to leave a stub like we would on a deciduous tree.  Thinning or pinching is done using the fingertips.  This avoids nasty cut-ends which result in brown tips to the foliage.  As new growth appears, it is carefully pinched out with the tips of the thumb and forefinger.  This forces new growth to appear further back in the foliage and reduces the length while creating a pleasing outline.  When pruning, be sure to leave foliage on a branch.  If all the foliage is cut off, the branch will most likely die.

For optimal health, the ends of each branch should appear open when viewed from above or below.  This ensures maximum light and air circulation – essential to the health of a juniper.  The profile when viewed from the side is shaped by wire and should have a shape you enjoy.  The most common shape is that of a pad, rather than a pom-pom.  Pads have slightly rounded tops with the branch seen running along the bottom and the branch tips angled up slightly.

Junipers are inexpensive and prolific – doubly so for the procumbens.  Don’t hesitate to experiement!  Despite having a reputation is an all-too-common bonsai, they can reward you with spectacular results when approached with a good plan, patience, and understanding of their needs!