JAPANESE BLACK PINE BONSAI

The Black Pine Bonsai: The Absolute King (Kuromatsu)

The Japanese Black Pine(Pinus thunbergii), called "Kuromatsu" in Japan, is considered the king of classical bonsai trees. It represents masculine strength, with its dark, wrinkled, armor-like bark and strong, prickly needles. It is a tree that commands respect and requires dedication: unlike deciduous trees, the pine does not easily forgive mistakes and requires specific pruning techniques (on "candles") to keep the needles short. However, once its physiology is understood, it is one of the most rewarding and long-lived species ever.

Origin & species

Native to the coastal areas of Japan and Korea, it is a tree accustomed to harsh conditions: strong winds, sandy soils and salty air. This origin explains its incredible hardiness and absolute need for drainage. There are valuable varieties such as "Corticosa" (corky bark) or "Yatsufusa" (very dense needles and buds), which are highly sought after by collectors.

Exposure and Microclimate

The Black Pine requires full sun, all day, all year round.
Direct light is the only way to activate the inner buds and keep the needles short and strong. If kept in half-shade, branches elongate, needles become weak and low branches die from lack of light. It is not afraid of wind.

Watering

Pine loves a controlled water regime.
Unlike deciduous trees, it prefers the substrate to dry well between waterings. Excess watering leads to long needles and, in the worst cases, root rot.
Tip: If you want short needles, reduce water slightly during the candle elongation period in spring (but don't let it dry out!).

Water quality

Not fussy. Tap water is fine. However, make sure it is not excessively saline or limey so as not to clog the porosity of the soil in the long run.

Substrate

Drainage is life or death. Pine trees breathe from the roots.

  • Recommended mix: 50% Akadama and 50% Kiryuzuna (Japanese substrate specifically for conifers).
  • If you cannot find Kiryu, use Pumice. Never use pure universal potting soil: it will suffocate the roots leading to the death of the tree.

Repotting

This is done every 3-5 years, in spring (April), when the candles begin to elongate.
Very Important: Pine trees live in symbiosis with a fungus called mycorrhiza (that white mold you find between the roots). Never wash the roots bare! Always leave some of the old soil loaf intact to preserve the mycorrhiza, which is essential to the health of the tree.

Fertilization

The Black Pine is a "glutton." To withstand tillage (shingling) it must be very strong.
Use solid organic fertilizer (the classic "patties") in abundance in the fall and spring.
Exception: If you want short needles, do not fertilize during candle elongation (May-June), but resume immediately after summer pruning.

Flowering and fruiting

Produces small cones (pine cones). On male bonsai they are often polliniferous (yellow) at the base of the candles. They should be removed because they weaken the branch and prevent retro-sprouting.

Structure pruning

Large cuts and removal of superfluous branches (pole selection) are done during winter rest (December-February).
Pine produces a lot of resin: cover the cuts with mastic to prevent resin from leaking everywhere and to protect the wood.

Maintenance pruning (Mekiri - Scandeling)

This is the key technique. In late June/early July, completely cut back the candles (the new shoots) developed in the spring.
This shock forces the tree to produce a "second expulsion" of buds in the summer. Having less time to grow before winter, these new needles will remain much shorter and more compact.

Stapling (Metsumi)

This is done in spring (April-May). If one candle is growing too strongly compared to the others, you "pinch" it with your fingers by breaking off its tip (one-third to one-half). This is used to balance the energy of the tree, restraining the strong branches and helping the weak ones.

Needle selection (Momiage)

In winter, old needles (2 or 3 years old) are removed and new needles are thinned to let light and air into the interior of the stakes. Without this operation, the inner shoots die and no new buds will be born.

Binding & folding

Pine wood is flexible and resinous, withstanding extreme bending.
The best time to tie is winter (after needle cleaning). Copper wire (cooked) is preferably used because it holds the bend better, but aluminum is also good to start with. The wire can stay up even a year or two, checking that it does not etch.

Diseases and pests

  • Red spider mite: Turns the needles grayish/yellow.
  • Cottonwood Cochineal: Lurks between the needles at the base of the candles.
  • Needle Fungi (Rust): Needles that become stained yellow/orange. Improve ventilation and sunshine.

Winter & protections

This is a very hardy and frost-resistant tree.
However, because the potted roots are exposed, if it freezes hard protect the pot. The foliage has no problem; in fact, the cold helps harden the plant.

Annual calendar

  • January-February: Needle selection, tying, structural pruning.
  • March-April: Repotting (if necessary), beginning fertilization.
  • May: Stapling of candles (Metsumi).
  • June-July: Candle cutting (Mekiri)-essential!
  • August: Rest, water checking.
  • September-October: Bud selection, strong fertilization.
  • November-December: Cleaning old needles.

Useful products for this bonsai

Frequently Asked Questions about Black Pine

Why are my pine's needles so long?
There are three causes: too much water, too much nitrogen at the wrong time, or (more likely) you did not do the candle cutting (Mekiri) technique in June. Without this technique, pine trees naturally tend to make long needles.

What is that white mold between the roots? Is it harmful?
Absolutely not! It is mycorrhiza, a good fungus that helps the pine tree absorb nutrients. It is a sign that the plant is doing great. When you repot, don't throw it away but mix some of that old soil into the new substrate.

Can I keep it indoors?
No, never. The Black Pine is a pure outdoor tree. In the house it would die in a few months from lack of light and temperature range.