This method of pine needle reduction has been used successfully by bonsai artists in our region for a number of years. It works with minor adaptations for all of the two-needle or black pines commonly trained as bonsai: Pinus thunbergii, densiflora, mugo, sylvestris, contorta and edulis. It may also be adapted for three-needle pines, such as Pinus ponderosa. Of course, starting with a tree which already has short needles will produce a more dwarfed effect sooner. The method is recommended for any tree that has already attained its full height and most of the desired branch ramification, but it can also be used successfully on younger trees in the course of their development. The old ways, such as withholding fertilizer and/or water might seem to help reduce needle length, but sometimes they led to the demise of the bonsai. Naturally, those methods cannot be recommended.
Almost all pine trees appreciate a somewhat coarse, free-draining soil mix. They usually resent over-watering and very shallow pots. Pines have a habit of strong growth at their branch tips and strongest growth in their uppermost leaders. The basic idea of this technique is to balance the areas of faster and slower growth so that the tree develops more uniformly than if left to its own choices. But this method Does Not Work on White Pines.
Begin feeding your pines not later than the middle of March weekly and weakly(every week with weak solutions of your favorite fertilizer(s). By late-April to mid-May, when candles have begun to lengthen, but before individual needles appear, examine your tree carefully to determine its overall vigor. If the tree is growing weakly or hardly at all, and no candles have pushed out a full one inch or more, DO NOT PROCEED with the needle reduction plan for this year. Instead, do one or more of the following: (1) continue feeding the tree, (2) expose it to more sunlight,(3) repot it into better soil and pause feeding for a month, (4) plant it in the ground or a much larger container for a year or two to rejuvenate it.
If you are
satisfied that your tree is growing well and that a number of
the candles have pushed more than one inch, break back the tips
of all the longest candles to a length of 1". Then set the
tree in a sunny spot, watering and feeding it until early summer.
Some artists allow all of the candles to push their maximum growth
without breaking them back at this time of year, but that should
only be used on trees in the early phase of development. Otherwise
it may produce heavy branches near the top of the tree, so be
aware and exercise caution. If you elect to use this method,
wait until late-June and begin the next part of the development.
more developed trees, where the branches are already in place
and have grown to their ideal lengths, do not cut off any of
the weakest shoots, which are those that have grown out to less
than 1". Remove the entire shoots longer than 1" from
the lowest one-third portion of the tree first(leaving 1/16"
stubs). Wait about a week to ten days and then remove all the
shoots over 1" from the middle branches (still leaving the
1/16" stubs). Finally, after another week to ten days, cut
off all of the remaining shoots from around the top of the tree
and at the tips of the upper, strongest-growing branches(still
leaving those 1/16" stubs on each branch tip). This will
balance the overall growth and give the weakest and middle areas
of your tree a head start over the strongest parts in their next
phase of development, the production of a new set of buds. At
this time just continue with your regular summer care until the
next part of the project.
Two weeks after the deciduous trees have shed their leaves, just before putting your pines into winter storage, it is time for the next part of the training. From this time onward until early January, you need to pluck off (or cut off short, leaving just the needle sheath) all of the three year old needles. Black pines usually keep needles for about three years. Nearest the trunk on each branch you should be able to see a set of the oldest needles, then a slight space and a set of newer, two year needles, and then at the very tip you can see the new buds, which will elongate into candles next April. The cutting-off-short method is preferable to plucking because new buds often form at the base two or three year needle fascicles. If you use the plucking method, pull the needles off in the direction of the branch tip. Never pull them back along the branch because it will damage the bark and any latent buds that you will want to preserve. On Pinus thunbergii only, continue plucking or cutting off some of the two year old needles as well, leaving only about three or four pairs intact on the tips of uppermost branches, five or six pairs on the tips of midlevel branches, and seven to nine pairs on the tips of the lowest branches. Be sure to keep a rosette of needles at each branch tip.
Now is a good time to begin wiring your tree. If major wiring is not needed, at least do the fine wiring necessary to turn each little rosette of needles upward at the tip. On species of pines other than thunbergii, it is best to leave more or all of the two year needles, depending on their overall vigor. For example, P. densiflora is a tree with a rather weak growth habit compared to other two needle pines and it should not be plucked agressively.
Then, after you do that last little bit of refinement wiring, put your tree into its winter storage and wait for spring, when the buds begin to grow and the cycle starts over. If you did not previously do the needle plucking or shearing in late fall or early winter, you can still shear the three year old needles back to a length of about 1/4", leaving the fascicles attached to the branches, as late as early-April. (You will not slow down the development of new long needles as much this year, but you will be starting on the right track for the future development of your tree.). They will be unsightly for a while, but the tree will shed the fascidles soon. You can also shorten the two-year needles by shearing them to about 1" long. The tips will probably turn brown unless you keep the tree under a misting system, but remember, these needles will be thinned in autumn and will eventually be shed. By that time this refinement method will be producing shorter needles on the bonsai. Further needle-shearing will then become unnecessary.
Each year continue this cycle and you will obtain new back-budding and increased secondary ramification as more sunlight penetrates to the interior of your pines. Within three years you are able to take charge of the development of your bonsai, making choices of your own instead of letting the tree decide, dwarfing even the most stubborn pines to achieve shorter needles. As you continue this method each year, your two-needle pines will attain ever greater refinement and character. They will become the envy of bonsai collectors everywhere.