Pinus Thunbergii

Submitted by: Charles E. Mashburn

Common Name(s):

Japanese Black Pine

Background:

Native to Japan, China, and Korea. Grows to about forty feet high in the wild. Originally brought to the U.S. by Japanese immigrants in the late 19th and early 20th Centuries, for use in landscape and as bonsai.

Sun:

Japanese Black Pine needs full sun, for at least five hours per day.

Temperature:

Black Pines are temperate, but do well in tropical environments, as reported by enthusiasts from Taiwan, Puerto Rico, and Florida. They are frost tolerant, and need little winter protection unless below zero temperatures are anticipated.

Watering:

Soil composition is critical. Black Pines must have freely draining soil, and are extremely susceptable to root rot and poor growth if the soil does not drain well.

Training:

Pruning is critical. In the fall, old needles must be removed, and fall is a good time to prune off the current year's overgrowth. In the spring, the new growth will show up as upright candlelike formations. Long candles must be removed completely, unless it is anticipated that they will be trained flat and become part of the tree's branch structure. Medium candles can be pinched back to half their length, and the smallest candles should be left alone.
Heavy pruning should only be done in the early spring.
Do not cut into bare wood when you prune. The tree will die back. Also, do not prune back past last year's needles.
In order to thicken the trunk, you will have to allow a sacrifice branch to grow -- either a string sucker near the base of the tree if you are lucky enough to have one or more sprout there, or a top branch that emerges from the back of the tree or from a place where the later pruning scar can be hidden by foliage.

Fertilizing:

Schultz evergreen fertilizer spiked with fish emulsion works best, and produces really good growth, as well as the back budding critical to good bonsai culture. In the fall, use Schultz bloom rite, to encourage formation of the candles (buds) for next spring.

Repotting:

In USDA zones 9 and 10, repotting can be done any time from November to about April, but if heavy work on the roots is contemplated, then do the repotting in February or March. Farther north, repotting should be done in the early spring just before the tree emerges from dormancy.
Periodically, a Black Pine in a bonsai pot may grow weak, or it may just not be thickening up or developing branch structure the way you want it to. Then you should repot it into a big tub, in a fifty-fifty mixture of decomposed granite and organic matter. This will restore the tree's health, and occasion rapid growth.

Propagation:

Seeds are about the only way to propagate Japanese Black Pine. Cuttings do not work, and although air layering sometimes works, it is extremely difficult.

Pests/Diseases:

Needle cast, which is a fungus, is the tree's worst pest. Do not water the tree's needles, except during the driest parts of the year. If there is any moisture on the needles at night during the cooler, wetter seasons, then needle cast may follow. First the tips of the needles will yellow, then the whole tree, and eventually the tree will weaken and die. During an El Nino year I have seen large old black pines in the landscape die from needle cast due to all the moisture. Use a copper based fungicide to prevent or stop needle cast.

Additional Comments:

It can take ten years to make a passable bonsai from a one gallon Black Pine nursery plant, and twenty to make a really good bonsai. I took a couple of my one gallon Black Pines to a bonsai nursery for pots once, and had my then three year old son with me. The proprietor looked at the trees and at my son and said "When he grows up, you're going to have some beautiful trees." My son is now eleven, and the proprietor was right. Be patient, and you will be richly rewarded.

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