Pinus thunbergii Seeds | Japanese Black Pine

Categories：Tree

Japanese black pine with paired dark needles and fissured bark — Japanese black pine (*Pinus thunbergii*): Pinaceae, native to Japan and Korea.

LATIN NAME: Pinus thunbergii

COMMON NAME: Japanese Black Pine

Plant Profile

Pinus thunbergii is the Japanese black pine, a coastal conifer of Japan and Korea, growing up to forty metres in the wild but usually much smaller in cultivation. The needles are in pairs, seven to twelve centimetres long, dark green and stiff, and the bark is grey-black and deeply fissured.

It grows on sand and rock near the sea, where salt spray and wind prune it into irregular shapes. That same toughness is why it has been trained as a garden tree for centuries, and why it is the classic species for Japanese black pine bonsai. The species is often confused with the red pine, which has longer, softer needles and a redder bark.

Science & Biotechnology

The species is resistant to salt spray because its needles have a thick cuticle and its roots tolerate saline soil, adaptations that let it grow closer to the shore than most pines. It is also tolerant of poor, dry ground, though it grows fastest in deep sand with a high water table.

The serious threat is pine wilt disease, caused by the nematode Bursaphelenchus xylophilus and carried by longhorn beetles of the genus Monochamus. Infected trees wilt within weeks and die, and there is no cure once symptoms appear. Quarantine zones and the removal of infected wood are the main controls, and Japan has lost large areas of black pine to the disease. Seed from coastal trees is collected in autumn, when the cones open, and it keeps well for several years in a sealed jar in the refrigerator.

Uses & Benefits

The tree is used for coastal shelterbelts, for timber and for garden training. In Japan it is the subject of niwaki pruning, in which branches are thinned into cloud-like pads over decades, and of bonsai, where the same species is grown in a pot for a century or more.

The wood is hard and resinous and was used for construction and for fuel. The young shoots are eaten in some regions, and the pollen is a seasonal allergen in Japan. As a garden tree it needs annual pruning in winter to keep its shape.

Growing from Seed

Seed germinates readily after a month of cold, or without any pretreatment if sown in spring. Sow on the surface, cover lightly, and expect seedlings in three to five weeks at 20°C.

Seedlings need full sun and free drainage from the start; shade produces soft growth that dies in the first winter. The tree is hardy to about minus fifteen and tolerates poor, sandy soil, but it needs space for its roots and does not like being moved. Prune in winter, when the sap is down, and never cut back into bare wood, since pines do not resprout from old stems.

Our Take

A tough coastal pine that becomes a garden tree only with decades of pruning, and one worth growing for the shape rather than the timber.

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