クロマツとアカマツの違い──見分け方と、庭師が変える手入れ(Japanese Black Pine vs. Japanese Red Pine: How to Tell Them Apart and How Gardeners Care for Each)

Japanese Black Pine vs. Japanese Red Pine: How to Tell Them Apart and How Gardeners Care for Each

Japanese black pine (kuromatsu, Pinus thunbergii) and Japanese red pine (akamatsu, Pinus densiflora) are the two pines most familiar in Japanese gardens. Drawing on government and research sources and on gardeners’ experience, this article illustrates how to tell them apart by needles, bark and winter buds, where each grows naturally, and how their different capacity to resprout changes how deeply they are cut and how their needles are plucked.

This article is part of our series on the pruning techniques of Japanese gardeners (niwashi, ueki-ya). Autumn and winter are the season for pine care, and we have already covered topics such as momiage, the plucking of old needles. This time the subject is the two kinds of pine, and why gardeners handle them differently even though both are simply called “pine”.

The two pines of the Japanese garden: the “male pine” and the “female pine”

Most of the trees called “pine” in Japanese gardens, temples and shrines are either black pine or red pine. Both are evergreen trees with needles in bundles of two, and both take two years to ripen their cones. They look alike, yet side by side their forms are quite different.

Garden pines are shaped into tiers and branch patterns over years of care, so their form differs greatly from pines grown naturally on mountains or coasts. The difference between the species is clearest in the natural form. Black pine has a thick trunk and stout branches and needles that spread ruggedly sideways. Red pine has a slimmer trunk that grows tall with curves, fewer branches and a lighter overall look. From this difference in impression, black pine has also been called omatsu (“male pine”) and red pine mematsu (“female pine”). A report of Japan’s National Institute for Land and Infrastructure Management (NILIM) explains that the name “male pine” is said to come from the stout, rugged look of its needles and branches, and “female pine” from its soft needles.

自然に育ったクロマツ(左)とアカマツ(右)。クロマツは幹が太く、枝が横へ張り、葉の茂みが重い。アカマツは幹が細く高く、幹の上の方(点線の円)は明るい肌になる

Gardeners tell these two apart not to name them correctly, but because they differ in their capacity to resprout and in the nature of their needles, which changes how deeply to cut, how much foliage to leave and how to pluck the needles.

How to tell them apart: needles, bark and winter buds

The surest sign is the needles. Black pine needles are 10–15 cm long and 1.5–2 mm wide, sharply pointed and stiff enough to hurt when you grip them. Red pine needles are about 7–10 cm long and 1 mm wide, slender and soft, and do not hurt when gripped.

1束の葉の比較。左のクロマツは太く硬く長い。右のアカマツは細くやわらかく、少ししなる

Next is the bark. Black pine bark is grayish-black and breaks into plates like a tortoise shell. Red pine bark is reddish; on the upper trunk and thick branches especially, thin layers peel away to leave a light reddish-brown surface. When identifying a tree from a distance, the color of the upper trunk is the best clue.

左はクロマツの幹。黒っぽく、亀甲状に厚く割れる。右はアカマツの幹。下は割れた灰色の肌、上は薄くはがれた明るい肌に切り替わる

In winter the buds also tell them apart. Black pine buds are thick and wrapped in whitish, silvery scales. Red pine buds are slender and reddish-brown. Looking at the shoot tips during the momiage season, the difference in color is easy to see.

枝先の冬芽(点線の円)。左のクロマツは太く白い。右のアカマツは細く赤褐色

Sources: NILIM, Conservation case studies of giant and old trees; Forestry Agency Tohoku Regional Forest Office, tree guide; NC State Extension, Plant Toolbox; Heibonsha World Encyclopedia (red pine buds).

There are also hybrids between the two. The Forestry Agency’s guide notes that the hybrid (ainokomatsu) may have silvery-white buds with red bark, or the reverse. Do not decide from one feature alone; look at needles, bark and buds together.

Where they grow: black pine on the coast, red pine inland

In nature, the two grow in different places. Black pine grows on the coast and tolerates salt wind; most of the pines in Japan’s coastal forests are black pines. Red pine grows inland on dry, poor ridges, and has been among the first trees to colonize bare land and hold the soil in place. Both prefer sun and good drainage, and both grow poorly in shade or in poorly drained ground.

左は海岸の砂地に自然に育つクロマツ。潮風で幹が陸の側へ傾く。右は内陸の乾いた尾根に育つアカマツ。どちらも下枝は落ち、葉は幹の上の方に集まる

The same traits show in gardens. From our field experience, black pine grows sturdily in gardens exposed to sea wind or in open, sunny places, while red pine does well in free-draining, rather dry soil. The NILIM report also rates root regeneration after root pruning as “poor” for black pine and “very poor” for red pine. Transplanting a red pine calls for even more careful planning than a black pine.

Differences in care: do not cut red pine hard

The biggest difference in care is the capacity to resprout. A booklet from the Sapporo Park and Greenery Association says that red pine has a weaker capacity to resprout than black pine, so it is better not to cut it hard when pruning. Pines in general rarely produce shoots from wood with no needles or buds, so the basic cut is at the fork of a young branch that carries needles. On top of that, red pine is cut even more lightly than black pine, only enough to tidy the shoot tips.

左のクロマツは、葉の付いた奥の分かれ目まで切り戻せる。右のアカマツは枝先に近い分かれ目で浅く切り、葉の付いた枝を多く残す(点線の円)

Among gardeners it is also said that red pine should be left with more needles than black pine, and that spring candle pinching should be restrained so as not to reduce the number of buds too far. The foliage is the tree’s strength, so you take less from the weaker of the two. This is a field rule of thumb that we could not confirm in primary sources.

In autumn momiage, the plucking itself differs. The same Sapporo booklet says that for black pine it is easier to hold the needles and strip them with both hands, and for red pine to pull the needles downward. Stiff, thick black pine needles come away together when the bundle is stripped. Soft, slender red pine needles slip through the hand when stripped, so they are pinched and pulled down. The hand moves differently because the needles are different.

もみあげの手つき。左のクロマツは葉を押さえてしごく。右のアカマツは古い葉をつまんで下へ引く(点線は手の動き)

On either pine, shearing the needles all at once with hedge shears is avoided. The Nagano Prefectural Forestry Research Center notes that clipping with large shears is the biggest cause of weakening pines.

The craftsman’s hand and eye: a feel for handling two pines

A gardener senses which pine it is the moment a hand goes onto the tree. Grip a black pine shoot tip and the needles push back even through a glove. Red pine needles bend in the palm and settle quietly. From our field experience, this difference in feel is the first signal that sets how strongly to work on the tree that day.

枝先の葉を手袋の手で握り、硬さで松を見分ける職人

The character of the two also shows in how they are trained. Black pine, with its stout, rugged branches, has been the leading tree for training into tiers with branches spread level. Red pine’s appeal lies in the line of its curving trunk, its red bark and the lightness of its few branches. Among gardeners, red pine is often finished not by packing it into tiers but by thinning branches so the trunk’s curves show, bringing out its natural form. The names “male pine” and “female pine” seem to carry this difference in handling too.

左は段に仕立てたクロマツ。右は幹の曲がりと軽さを生かしたアカマツ。枝の間から幹の線が見える(点線の円)

Even under the same words “pine care”, misreading the tree means taking too many needles that should have stayed, or cutting branches that will not come back. Touching with the hand, looking up the trunk with the eye, and adjusting the amount of work to the strength of each tree: this balance, which no manual can fully write down, is the part handed down from master to apprentice on site.

What the two pines share: timing, and pine wilt disease

The timing is the same for both: spring candle pinching around May, and autumn-winter momiage from around October. The training text of the Japan Federation of Landscape Contractors says that in momiage about 30–40 needles (15–20 pairs) are left at the tip of the current year’s shoot. Timing is covered in detail in our article on when to prune.

The other thing they share is vulnerability to pine wilt disease. The pine wood nematode, less than 1 mm long, is carried into the tree by the Japanese pine sawyer beetle, stops the flow of water and kills the whole tree. Both red pine and black pine are affected. Across Japan, resistant red pines and resistant black pines, confirmed to tolerate the nematode, are being bred. Noticing how needles change color and how branches die during routine care also helps catch this disease early. The mechanism is explained in our article on pine wilt.

Frequently asked questions

Q1. How do you tell Japanese black pine from Japanese red pine?

A. Look at the needles, bark and winter buds together. Black pine needles are 10–15 cm, thick, stiff and painful to grip; its bark is grayish-black and breaks into tortoise-shell plates; its winter buds are whitish. Red pine needles are 7–10 cm, slender and soft; its upper trunk has light, reddish bark; its winter buds are reddish-brown.

Q2. Which pines are the “male pine” and “female pine”?

A. Omatsu, the male pine, is black pine, and mematsu, the female pine, is red pine. Black pine is said to be so called from the stout, rugged look of its needles and branches, and red pine from its soft needles.

Q3. What should you watch for when pruning red pine?

A. Do not cut it hard. Red pine has a weaker capacity to resprout than black pine, so cut lightly at the fork of a branch carrying needles, just enough to tidy the tips. Leave more needles too, and never cut partway along old wood with no needles or buds.

Q4. Is momiage done differently on black pine and red pine?

A. The plucking differs. On stiff black pine it is easier to hold the needles and strip them with both hands; on soft red pine, to pinch the old needles and pull them downward. For both, the season is autumn to winter.

Q5. Which is better for a garden, black pine or red pine?

A. It depends on the site. Black pine tolerates salt wind, grows sturdily in open, sunny places and suits training into tiers. Red pine prefers free-draining, rather dry soil and suits a natural form that shows off its curving trunk and lightness. Both dislike shade and poor drainage.

Sources

– National Institute for Land and Infrastructure Management. Conservation case studies of giant and old trees (Kyoju roju no hozen taisaku jireishu). NILIM Report No. 566, January 2010, pp. 121, 148.
– Forestry Agency, Tohoku Regional Forest Office. Tree guide: Akamatsu; Kuromatsu.
– Saitama Prefecture, Omiya Park. “The red pines of Omiya.”
– Forestry Agency. “Pine wilt damage (Matsukuimushi higai).”
– Niigata Prefectural Forest Research Institute. “On nematode inoculation tests of resistant black pine.” November 2019.
– Sapporo Park and Greenery Association. Sukusuku Midori No. 21: Growing healthy garden trees — training and pruning, pp. 7–8.
– Japan Federation of Landscape Contractors. Zoen shokyu gino no tebiki (Guide to basic landscaping skills), revised edition. March 2015.
– Nagano Prefectural Forestry Research Center. Mini Technical Note No. 11, “Pruning Pines”. May 1999.
– NC State Extension. Plant Toolbox: Pinus thunbergii; Pinus densiflora.
– Heibonsha World Encyclopedia, “Akamatsu” (via Kotobank).

Masatoshi Nakamura
Jumokui (Tree Doctor), Toshi Landscape Co., Ltd., Tokyo