Rocky Mountain Maple

Rocky Mountain maple presents itself as a small broadleaf tree with a distinctly upright multi-stemmed habit, often shrublike in dense plantings but reaching 30 feet tall in open settings. You recognize it by its opposite, compound leaves divided into three to five lobes with coarsely double-toothed margins, displaying bluish-green undersides and achieving brilliant yellow fall color tinged with red. In spring before the leaves fully emerge, tiny yellowish-green flowers bloom in compact clusters; these give way to winged fruits (samaras) spreading nearly parallel, a subtle but distinctive detail. The smooth dark bark lacks the hairs that earned its species name 'glabrum.' Native throughout the Pacific Northwest's rocky mountain streams and coniferous woods, this slow-growing tree thrives in moist to moderately dry soils and full sun to part shade.

Site rocky mountain maple in full sun to part shade with moderate soil moisture; the tree tolerates poor soils and adapts to both acidic and alkaline conditions. Once established, it demonstrates moderate drought tolerance, though performance improves with consistent moisture during hot, dry spells. PNW records document both common and specialized pathogens affecting maples: monitor for verticillium wilt, leaf spots, powdery mildew, and anthracnose in wet seasons; less commonly, tar spots, nectria canker, and leaf scorch appear under stress. Pests of concern include maple bladdergall mite, cottony maple scale, and various aphids, though native trees usually manage these without intervention. The slow growth rate and variable multi-stem form make it ideal for naturalizing in dry rocky areas where you want native character without the maintenance of faster species. Prune in summer to avoid excessive sap bleeding from wounds.