The 'Kotobuki' Japanese Black Pine Bonsai: Effortless Elegance

The 'Kotobuki' Black Pine is a prized and much sought-after cultivar of the classic Pinus thunbergii. In Japanese "Kotobuki" means "Long Life" or "Congratulation". Bonsai growers love it because it solves the main "problem" of the black pine: needle length. This variety naturally produces very short, stiff needles of a deep dark green, and has a compact growth habit that makes it look like an already mature, refined pine even when young. It is the ideal choice for those who love the powerful bark of the black pine but want a less demanding canopy to manage.

Origin & species

It is a mutation (sport) of the Japanese Black Pine. It keeps the rough, dark bark typical of the species (although it takes a little longer to develop it than the wild type), but has weaker apical dominance and denser ramification. Kotobuki bonsai are often grafted onto wild black pine roots to give the plant vigour, while keeping the genetic foliage of the Kotobuki.

Position and microclimate

Like all black pines, it demands full sun.
Direct light is vital to keep the inner needles healthy and to stimulate the production of new buds. Shade leads to thinning branches and a weakened plant. Give it a very well ventilated position to prevent fungal problems and scale insect among the dense needles.

Watering

The Kotobuki dislikes waterlogging.
Water only when the soil mix is thoroughly dry. Compared to the classic black pine, the Kotobuki grows slightly more slowly and uses a little less water. Always check the moisture of the substrate with a finger before watering. Excess water can turn the needles yellow or lead to root rot.

Water quality

It is not demanding. Tap water is fine, provided it is not excessively hard or saline over the long term.

Substrate

Drainage must be perfect; it is the key to healthy pines.

• Recommended mix: 50% Kiryuzuna (specific for conifers) and 50% Akadama.
• If you cannot find Kiryu, pumice is an excellent alternative. Absolutely avoid pure universal potting composts, which suffocate the roots and the mycorrhiza.

Repotting

Carry it out every 3-5 years, in spring (April), when the candles start to move.
Never bare-root wash the roots. It is essential to preserve the mycorrhiza (the white symbiotic fungus) present in the old soil mix, which helps the tree absorb nutrients. Always reintroduce some of the old mycorrhizal soil into the new mix.

Fertilizing

Feed with solid organic fertilizer in autumn and spring.
For pines, specific fertilizers such as Joy Tamahi are excellent: thanks to its supply of organic nitrogen it encourages needles of a deep, bright green.

Flowering and fruiting

It produces small cones, but these should be removed if the plant is in the refinement stage, so as not to waste energy needlessly.

Structural pruning

Large branches are cut during winter dormancy (January-February).
Always use cut paste on the cuts, since the resin does protect but exposed wood can be an entry point for pathogens.

Maintenance pruning (the difference from the classic pine)

Here lies the big difference: the Kotobuki does NOT necessarily need Mekiri (complete candle removal).
While on the normal black pine the candles are cut in June to obtain short needles, on the Kotobuki the needles are already short!
If the tree is balanced, limit yourself to bud selection (leaving 2 per branch) in winter. If you carry out Mekiri on a weak Kotobuki, you risk it not flushing out new growth, or producing buds that are too small.

Pinching (Metsumi)

In spring, when the candles elongate, you can pinch them (breaking off a piece with your fingers) only if some are running away far stronger than the others. The aim is only to balance strength, not to reduce the needle size, which is already perfect.

Wiring & bending

Apply the wire in autumn/winter. The branches are flexible but, as they grow dense, take care not to crush the needles between the wire and the bark. Copper wire is preferable for holding power, but aluminium works perfectly well.

Diseases and pests

• Cottony scale insect: It easily nests among the short, dense needles of the Kotobuki. Check the inside of the canopy often.
• Red spider mite: Causes yellowing of the needles.
• Fungi (rust): If ventilation is poor.

Winter & protection

Frost hardy. It can stay outdoors all year round.
Protect the pot with mulch only in the case of exceptional prolonged frosts, to safeguard the pot and the fine roots.

Yearly calendar

• January-February: Cleaning off old needles (essential to let light in!), bud selection.
• March-April: Repotting (if needed), fertilizing.
• May: Light pinching only on strong candles.
• June-July: Pest checks; complete candle removal is NOT needed.
• August: Rest, regular watering.
• September-October: Autumn fertilizing (important).
• November-December: Wiring.

Useful products for this bonsai

• Kiryuzuna (top substrate for pines)
• Joy Tamahi fertilizer (ideal for the green of conifers)
• Bonsai tweezers (for removing old needles)
• Copper-coloured aluminium wire (for styling)
• Cut paste (cut protection)
• White oil (against scale insect)

Frequently asked questions about the 'Kotobuki' pine

Why does it cost more than the normal black pine?
The Kotobuki is a slow-growing and highly appreciated variety. Moreover, most quality specimens are grafted and grown on for years before being put on the market. The price reflects the time saved: you buy a pine that already has perfect needles, without having to work for years to obtain them.

What happens if I cut the candles (Mekiri) as on a black pine?
If the plant is very strong, it will survive but will produce minuscule needles. If the plant is average or weak, you risk the branch stalling or dying. Generally, on the Kotobuki, Mekiri is avoided or carried out only partially on overly vigorous branches.

I can see a swelling at the base of the trunk, is that normal?
Yes, it is the graft point. Almost all Kotobuki are grafted onto wild Black Pine roots (Thunbergii type) to guarantee strong roots to a plant that would genetically be weaker. With time and cultivation, the graft mark will blend in.