Japanese Black Pine Care Guide
Pinus thunbergii is considered a classic bonsai tree. It is native to - and common in - Japan, and can grow upwards of 100 feet tall in ideal conditions. In most cases, however, it may reach a height of 20-25 feet, achieving a spread of 20-35 feet wide. In its native land the Japanese Black Pine is often used as an ornamental in parks and gardens.
The branches of this conical pine have a unique, horizontal growing pattern, resulting in a layered look. The needles are dark green, grow in pairs, and are considerably long at three to five inches. One of the most attractive features of this tree for bonsai purposes is the bark – it is grayish to gray-black with irregular fissured plates, giving it a lovely textured look of age.
It is possible to grow Pinus thunbergii in warmer climates, however it does not prefer extreme heat and is happiest in fairly cool zones. It will, however, require protection if temperatures dip unusually low. This tree enjoys being grown outside in full sun with good air circulation.
Japanese Black Pine is hardy and drought-tolerant. It may be allowed to dry out between waterings, and may also benefit from the use of a humidity tray or daily spritzing with water, particularly in the heat of summer.
Feed an acid-based fertilizer about once a month. A balanced mixture may be used every one to two weeks during the growing season, typically spring to fall.
Styles – Japanese Black Pine may be shaped into most bonsai forms except cascade. This species is most conducive to informal and formal upright. The trunk often develops a natural sideways lean which may lend itself to slanting.
Pruning should be done in early spring, with pinching taking place in late spring after the buds have developed. Start with pinching the weakest undesired buds, then wait a week and pinch off the strongest undesired ones. Once this first round is complete, identify the weakest areas of growth and remove the weakest buds. In the stronger areas of foliage, remove the strongest buds, leaving the weakest.
If shaping is desired for a more distinct silhouette, plucking may be carried out by removing needles from the tops and bottoms of the branches and leaving the lateral ones.
As long as the bonsai is healthy, remove new candles every other year in the spring. This will stimulate the production of new buds on those sites when autumn comes. This method helps to reduce the length of the needles and encourages the foliage to become dense. The Black Pine does take well to wiring as the branches are very flexible, just be careful when wrapping and bending to avoid cracking the bark. Because of the malleability of the branches, wire may need to be left on longer than normal.
Pinus thunbergii may be propagated from seed, grafting, or cuttings. To propagate from seed (which should be done in April) soak the seeds in water for two days prior to sowing in sand. Throw away any seeds that float in the water.
Repot your Japanese Black Pine bonsai in spring, before swelling of buds. This can be done every two to three years for younger trees and every four to six in older specimens. This species prefers a larger pot to allow enough room for the feeder roots to thrive. Pines should not be root-pruned too aggressively, although the Black Pine is a bit more tolerant than most and can probably handle the removal of up to a third of its root system.
Many plants, particularly evergreens, rely on a symbiotic relationship with a fungus called Mycorrhiza. This organism lives in the root system of the tree and assists the roots in absorbing nutrients, thus pines should never be bare-root because you want to maintain this beneficial relationship even between pots. The soil should be very well-draining – 75% aggregate with 25% organic (such as pine bark) works well. As with most bonsai, place the pot in a shady location after transplanting, and keep moist while the roots take hold in their new home.
Insects/Pests & Diseases:
This tree is vulnerable to a number of common bonsai pests such as aphids, sawfly, mealy bugs, and borers. If insects are visible a systemic insecticide may be necessary.
While Japanese Black Pine is resistant to most diseases, it can fall prey to that enemy fungus of all pines, needle cast. The tips of the needles may turn brown and sometimes rings of discoloration appear up the shaft of the needle. While the problem can be treated with fungicide, the needles will not be restored to their normal color. The best course of action to avoid needle cast in Japanese Black Pine and most other pine bonsai is to use a preventative spray regimen.