Limber Pine, Pinus flexilis
Is your city’s planting list feeling a little too rigid these days? Flex your options by trying Pinus flexilis! The limber pine is hardy in USDA hardiness zones 4-7A and may be better adapted to conditions in Eastern Washington than those west of the Cascades, since it is not fond of wet feet. That said, this evergreen conifer is so interesting that it might be worth a try in any landscape.
The limber pine’s native range is the Intermountain West, occupying portions of the Great Basin area as well. You may be raising a skeptical eyebrow about its suitability hereabouts, but hear me out; any urban forester worth their sawdust is willing to take a chance on an interesting tree with such great attributes. Limber pine, also known as Rocky Mountain white pine, is found on sites that are hot, dry, windy, rocky and steep, and performs best in full sun with well-drained soils, requiring little irrigation once established. The most interesting feature of the limber pine are its extremely flexible branches—“limber” to the point of seeming strange and unnatural: young branches can actually be tied in knots without fracturing the tissue! Such knots, as the branches grow, appear to have little to no impact on the health of the limb. Due to this flexibility, limber pine handily withstands heavy loading from wind, water, ice, and snow.
If you were to guess that the adaptability of this tree to harsh, extreme conditions is an indicator of its toughness in urban situations, you would have guessed correctly. A little research reveals that this tree is already being used well outside its native range, in mid-western states such as Illinois, Missouri, and Minnesota. At least three limber pine are growing exceptionally well on the campus of Whitman College in Walla Walla. To make it even easier to use limber pine in local landscapes, production nurseries are introducing new cultivars such as “Vanderwolf’s pyramid”, a dense pyramidal tree with tight, twisted, silvery blue-green needles; “extra blue”, similar in form and shape to Vanderwolf’s pyramid but growth is slightly irregular and needles are a deep steel blue; and “Columnaris”, a fastigate form with blue-green needles.
The limber pine is so tough, adaptable, and low-maintenance that you may be wondering, “What’s the catch?” Remember that limber pine is in the white pine family; and like its cousins, is particularly vulnerable to white pine blister rust and parasitic colonization by dwarf mistletoe if those are in your area. Mountain pine beetles, weevils, and budworms are known to feed on limber pine, and it is susceptible to Armillaria, Phaeolus and Phellinus, although these are not widespread issues.
Mature limber pined are slow growing trees. In their native habitat they may reach heights of 60 to 65 feet, however in an urban landscape its growth is expected to be 20 to 25 feet in height and a 10-t0-15-foot spread over a 20-year period. Thin silver-gray bark on young trees matures to nearly black in older trees, with an interesting scaly, platy texture. Cones are approximately 6″ long with thick, stout scales. Occasionally cones will be twisted along their axis, providing additional interest.
Altogether, a tough, interesting, unusual “Tree to Try”!
(All photos taken by Tree Link Editor Ben Thompson of limber pines located on the Whitman College Campus, Walla Walla, WA)