Attractive in All Seasons: Mugo Pine
By Corinne Kennedy
Mugo pine, low-growing and skillfully pruned, is planted near the pond in the Seattle Japanese Garden. (photo: Corinne Kennedy)
I’m a tree and shrub aficionado, and conifers (cone-bearing woody plants) are my personal favorites! I feel very fortunate that my West Seattle home, on a relatively large lot, is sheltered by huge native trees, including one douglas fir tree (Pseudotsuga menzesii) and three western red cedars (Thuja plicata). In the heat of summer, at home or on summer hikes, the refreshing scent of their foliage brings me so much happiness!
I especially love the bold foliage, living architecture, and worldwide historical significance of pine trees. They’ve been the subject of stories and legends over millennia, renowned for their toughness and adaptability. Most species tolerate cold temperatures, poor rocky soil, wind, and drought. They also develop striking character with age, especially with skillful pruning or the effects of temperature and wind.
Although I don’t have room in my garden for a large pine species, such as ponderosa pine (Pinus ponderosa), a smaller species has found a home there. Readily available but often undervalued, Pinus mugo (commonly known as mugo pine) is also planted in the Seattle Japanese Garden. Other common names are dwarf mountain pine and European mountain pine. It’s not native to Japan or to the Pacific Northwest and generally does not attain the impressive stature of some of the Garden’s other pine trees. Nonetheless, many attractive cultivars of this species are readily available at retail nurseries—and eminently suitable for Japanese-style gardens and small urban gardens generally. The Seattle Japanese Garden contains more than 20 mugo pines, including two specimens of the dwarf cultivar Pinus mugo ‘Slowmound’. Many are planted near the Garden’s central pond.
This article, about Pinus mugo, is a follow-up to my two previous blog articles, posted in 2019, about the genus Pinus and the two most important pine species native to Japan:
Pinus mugo, a Description:
Pinus mugo (formerly spelled mugho or mughus; and before that listed as Pinus montana) is native to the mountains of central Europe—including the Carpathians, Balkans, and Italian Apennines. The genus word, Pinus, is the Latin word for “pine tree.” The specific epithet mugo comes from the Italian pino mugo, meaning "small mountain pine." Plants were introduced into Britain and Scandinavia in the second half of the 18th century and became popular in the United States about 100 years later.
Mugo pine is generally a shrublike, multi-stemmed evergreen conifer. In its native range, though, it varies in size and habit from a low, sprawling shrub to a relatively large tree. Plants (often referred to as Pinus mugo var. mugo or Pinus mugo subsp. mugo) are typically two to six feet tall, bushy, and very wide-spreading, but in the wild some grow much larger (30 - 80 feet tall and wide). In gardens, however, treelike forms are generally much smaller, growing to about 15 ft. tall.
Unfortunately, authorities disagree about whether the treelike forms are a form of mugo pine, Pinus mugo var. rostrata, or a separate species, Pinus uncinata. As a Seattle Japanese Garden visitor or volunteer, please feel free to ignore such taxonomic disputes about the treelike forms and focus instead on the attractive and useful low-growing mugo pines that are the subject of this article!
The bark of mugo pines is grayish-brown and scaly, splitting with age into irregular plates. The young shoots are short and smooth, with prominent ribs. Initially a light greenish-brown, they darken with age.
Prominent winter leaf buds are known as “candles.” They are cylindrical in shape, pointed, and about ½ inch long, with resinous reddish-brown scales. In the spring, they elongate before opening up into thick green needles, held in bundles of two, which persist for at least five years. Blunt-tipped and curved or slightly twisted, they are medium to dark green, and 1 to 2 inches long, with finely toothed margins. During the winter months, the needles of some plants turn yellowish-green.
Female (seed-bearing) cones are dark brown, stalkless (or short-stalked), egg-shaped, and 1 to 2.5 inches long. They are held in groups of one to four, generally pointing outward or at a slightly pendulous angle. The male (pollen) cones are greenish-yellow and ¼ inch long.
Pinus mugo, botanical drawing. (image: Zelimir Borzan, University of Zagreb, Creative Commons 3.0)
Pinus mugo is hardy to at least USDA Zone 3 (minimum temperature -40 degrees Fahrenheit) and grows best in full sun and well-drained soil, with good air circulation. It is drought tolerant when established and tolerates soils of varying pH levels and textures, including alkaline and clay soils, if they are well drained. It is very tolerant of urban conditions and environmental salt, but does best in cool summer climates, such as the Pacific Northwest. It takes well to pruning and is relatively easy to transplant.
In its native range, mugo pine protects soils from erosion and avalanche damage, and is used to produce oil, turpentine, medicines, and food. In Bulgaria, the needles are used to make tea.
Mugo pine is resistant to damage by deer, but stressed plants may be susceptible to damage from insects (scale, sawflies, borers) and diseases (tip blight, rust, rot).
Not a Dwarf Species:
The species plant, Pinus mugo, is not a dwarf plant and is no longer commonly available at retail nurseries. Even in the past, plants sold at retail were often labeled Pinus mugo var. pumilio, indicating low-growing selections produced from seed and thus relatively inexpensive. That variety and another seedling selection, Pinus mugo ‘Nana’, are usually pruned by the grower to improve their appearance and salability. As seed-grown plants, however, their growth rate and ultimate size are unpredictable. Most will outgrow typical residential garden spaces—other than very large, sloped areas—unless they are pruned annually, beginning when they’re first planted.
In the Seattle Japanese Garden:
In the Seattle Japanese Garden’s plant inventory, most of the mugo pines are listed as simply Pinus mugo, but like many other pine species in the Garden, they are subject to a highly skilled and rigorous pruning regimen—pinching of their candles in spring, followed by a major pruning in autumn. Here are links to two pruning articles written by SJG staff gardeners:
Dwarf and Miniature Cultivars:
Fortunately for gardeners who prefer to avoid a commitment to annual pruning, more than 100 cultivars of mugo pine have been developed, including many compact forms. The latter include plants of two “growth types,” as defined by the American Conifer Society:
Pinus mugo ‘Hvozdany’, a miniature cultivar planted in my garden, next to a miniature New Zealand flax. At 18 inches tall and slightly wider, it’s at least 20 years old. (photo: Corinne Kennedy)
Miniature—growth of less than 1 inch per year, with a potential 10-year height of about one foot.
Dwarf—a relatively large category that includes plants that grow from 1 to 6 inches per year, with a 10-year height of one to six feet. In the case of dwarf mugo pines, the plant’s 10-year size may be relatively low and wide-spreading.
Pinus mugo ‘White Bud’ in my own garden. At 30 inches tall and 3 ft. wide, it’s probably about 15 years old. (photo: Corinne Kennedy)
Compact cultivars may be small-growing uprights, rounded in form, or ground-hugging plants that are usually much wider than they are tall. Both miniature and dwarf types are appropriate for small urban gardens or small spaces within a larger garden. Retail nurseries often stock compact-growing plants with green, gold, or variegated foliage. They are useful and attractive when planted in containers, used as small focal points, or planted in rockeries, rock gardens or foundation beds.
The following Pinus mugo cultivars are dwarf types (according to the American Conifer Society’s definition), generally available at retail nurseries: ‘Mops’, ‘Sherwood Compact’, ‘Slowmound’, ‘Valley Cushion’, ‘White Bud’, and ‘Winter Gold’. As cultivars, they are “clones” propagated from cuttings (and sometimes also grafted on a different rootstock). Unlike plants grown from seed, which often do not resemble the parent plants, they have predictable growth rates, habits and 10-year sizes.
Corinne Kennedy is a Garden Guide, frequent contributor to the Seattle Japanese Garden blog, and retired garden designer.