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Japanese Black Pine

Tree of the Month - November 2002: Pinus Thunbergii - Japanese Black Pine

Pinus Thunbergii - Japanese Black Pine
Family: Pinaceae

By John Hill

The Japanese black pine, ( Pinus Thunbergii ) is among the very best species of tree for bonsai. This pine was named after Dr. Carl Peter Thunberg, a Swedish student of horticulture who traveled extensively in Java and Japan. This species has long been regarded by many as the "king" among bonsai. Few trees can convey the stoic power of bonsai that a black pine can. It is also a strong tree that responds well to the techniques used in bonsai.
The black pine is a very vigorous tree commonly grown in Japan where heights up to 75-80 feet are commonly reached. P. thunbergii are very tolerant of poor growing conditions, surviving in nature on barren, stony soils. It has thick, dark, green gray needles up to 5-7 inches long borne in groups of two. Though these needles are quite long, the size can be reduced in length with the use of bonsai pruning techniques. A twice-yearly pruning will create flat pads of very dense short branches and completely control the size and shape of this unique tree.

In June remove all the new candles that are longer then one inch. Many new shorter candles will form a whorl of short branches. In November reduce this whorl of branches to a flat forked branch. In this manner, 3-inch needles may be reduced to 2 or even 1 inch. Every other spring, if the tree is healthy, you can remove all the new candles. The following fall, buds will appear where the candles were removed. This greatly shortens the internodes and increases foliage density.

Black pines require full sun and good air circulation. Don't forget to turn the tree from time to time so that light reaches all parts of the foliage. P thunbergii does not like extreme heat, though, especially in the area of its roots. Spray the foliage with water daily during the hottest days of summer. Move to where it only gets a half a day of direct sun to help keep the roots from over heating.

Watering your black pine can be tricky. They may be allowed to go dry between watering but do not over water. Too much water will cause undesired growth in a finished tree. With time and experience you can hold off on the water until the very last minute without letting your tree suffer. If you tend to water often use more aggregate in your soil mix. The mix that I use consists of 50% calcined clay, 30% pine bark, and 10% peat.

Repot in early spring or late summer, every 2-3 years for young trees and 3-5 years for older ones. The first pruning to position the roots will coincide with repotting and reduction of the crown (preferably in early spring). Always leave a good root system. The container may have to be larger that aesthetics dictate so the feeder roots do not dry out and die at the end of a hot summer day. Don't under pot a black pine. To take up nourishment, pines need to have a special type of fungus (mycorrhizae) in the soil around the roots. This fungus appears as a white, stringy material. When repotting, make sure some of this helpful fungus is included in the new soil mix.

Japanese black pine has been a favorite in costal plantings because of its excellent salt spray and soil salt tolerance and its function as a wind screen. But in the last few years, it has been showing up in plant clinics far to frequently.

The main pest causing Japanese black pines to die in large numbers is the turpentine beetle (Dendroctonus terebrans) which frequently carries with it the bluestain fungus (Leptographium spp.) These beetles typically feed on the inner bark of the lower trunk and may even girdle the tree. Characteristic signs of the turpentine beetle injury include long clumps of hardened sap around the lower trunk and reddish sawdust around the very small entry holes. In addition, the introduction of the bluestain fungi can destroy cambial tissue and compound the injury caused by the beetles. A pine affected by this pest complex will show a yellowing or rusty browning throughout the entire tree before the foliage begins to die and needles begin to drop, often within the year.

European pine shoot moth causes young shoots to fall over. Infested shoots may extrude resin. The insects can be found in the shoots during May. Pesticides are only effective when caterpillars are moving from over wintering sites to new shoots. This occurs in mid to late April or when the needle growth is about half developed.

Bark beetles bore into trunks making small holes scattered up and down the trunk. The holes look like shot holes. Stressed trees are more susceptible to attack, so keep trees healthy. Sawfly larvae caterpillars feed in groups on the needles. Sawflies can cause rapid defoliation of branches if left unchecked. Pine needle scale is a white, elongated scale found on the needles. Pine tortoise scale is brown and found on the twigs. Most scale can be controlled with horticultural oil. Aphids, mealy bug and red spider mites, scale, shoot tip moths and beetles may attack the tree and can best be controlled with a systemic insecticide. Do a preventive fungicide spray every two to three weeks with Benomyl or Daconil. This pine is resistant to Diplodia tip blight.


Species Guide: Japanese Black Pine
By Keith Scott

Species: Common name: Japanese Black Pine
Botanical name: Pinus Thundergii
Japanese name: Kuromatsu

Advantages: Readily available; widely heralded as the foremost pine bonsai; good bark; tolerates water but must have first rate drainage; develops adventitious budding on old wood when kept healthy; easily wired, takes to pruning well.

Disadvantages: Not reliably hearty north of Pittsburgh; needles can be too long for good proportions; pine needle cast and needle scale can damage or even kill a weak tree.

Suitability as Bonsai (1 is least suitable 10 is most suitable): 8

Growing Location: Full sun

Watering: The Japanese Black Pine will tolerate wet conditions if proper drainage is present. Keep coarse soil damp to touch.

Propagation: Seed or with dwarf or specialty forms by grafting.

Fertilizing: Use a balanced fertilizer every week or two during the growing season.

Over-wintering: The Japanese Black Pine needs protection from winter temperatures below 0oF. A variety of constructions can help the pine survive: a poly house is ideal but stacking hay bales around the tree helps along with mulching several inches over the pot and the trunk.

Styling: Informal and formal upright as well as many other styles except cascade.