Red Maple or Swamp Maple

(Aceraceae - Maple Family)

Form

• large shade tree
• species form matures at about 70' tall by 40' wide, although the many cultivars are smaller
• upright oval to upright rounded growth habit in youth, but often developing several main upper trunks with age to yield an upright irregular growth habit for the mature species form, and an upright rounded growth habit for most mature cultivars
• medium growth rate

Culture

• full sun to partial sun (partial shade tolerant in youth)
• prefers moist acidic soils, but will tolerate wet soils or moderately dry soils ranging from acidic to neutral pH
• alkaline soils (those with a pH above 7.5) usually cause leaf chlorosis (a yellowing of the leaf blades, often with pronounced green veins) and a weakly growing tree, especially among the cultivars, due to manganese nutrient deficiency that leads to nitrogen deficiency, resulting in poor chlorophyll production and stunted growth
• propagation of the cultivars is by budding onto seedling understock or rooted stem cuttings, while the species form, although rarely propagated, is by rooted stem cuttings or by seeds
• Maple Family, being prone to Verticillium Wilt as a pathogenic disease, and leaf scorch and leaf chlorosis as physiological diseases; several pests can also occur
• abundantly available, usually in ball and burlap but increasingly in container form, with many cultivars
• Red Maple is somewhat sensitive to being transplanted in Autumn, and care should be taken to amend the soil, fertilize, water thoroughly, mulch adequately, and avoid Winter salt spray, to enhance survival chances during the first Winter

Foliage

• opposite, with the leaf blades having medium green uppersides and light green to silvery undersides, the latter of which are noticeable with strong breezes as a subtlely bicolored foliage
• three- (or five-) lobed, the basal two (if present) much smaller than the upper three, with each of the lobes serrated and sometimes lightly incised
• palmate veination, with the blades about 3" long and 3" wide
• chlorotic foliage may occur, usually resulting from manganese deficiency in alkaline soils
• fall color of the species ranges from bright yellow to orange to red (most cultivars have outstanding fall color in various shades of red)

Flowers

• globular to pendulous clusters of red inflorescences may occur as early as late January, but often open in late March to early April
• noticeable long before the foliage emerges, and while not especially showy, they are somewhat ornamental since little else is flowering at this time of the year
• trees can be predominately staminate (male), pistillate (female), or monoecious (an even mix of staminate and pistillate flowers on the same tree), and for this reason, some trees will be much heavier in subsequent fruit production than others

Fruits

• two samaras per stalk, having semi-divergent (45 degree angle) wings, in pendulous clusters from the stems, maturing to red-brown in October, but often in reduced quantity or not present at all on many of the cultivars

Twigs

• red stems with off-white lenticels occur on mature first-year wood, with bright red buds in Winter; twigs soon turn into smooth silvery-gray branches
• lower branches on mature trees are not nearly as pendulous with upturned ends as those of Silver Maple (Acer saccharinum), a closely related species with which Red Maple can naturally cross-hybridize

Trunk

• for the species form, the young gray to silver trunk and branches will fissure to yield exfoliating strips of dark gray or black bark with age, but for many cultivars, the degree of fissuring and darkly colored bark is lessened

ID Summary

• predominantly three-lobed leaves are serrated with acute lobes and usually without incisions, having a subtle bicolor effect in the breeze due to their green-silver undersides
• first-year stems are red-brown with obvious bright red Winter buds, many of which yield red pendulous inflorescences in late Winter; more mature stems and branches are a smooth, silvery-gray, gradually transitioning to bark that is darker and more furrowed to platy on mature trees
• fall color ranges from a good to spectacular yellow or red within the species, but is consistently red and always spectacular among the many cultivars

USAGE

Function

• shade, specimen, Autumn accent, or wet site tree
• often innappropriatley used as a street tree (it does not respond well to urban stresses, usually gets too large, and has surfacing roots even in youth)

Texture

• medium texture in foliage and when bare
• thick density in foliage but average density when bare

Assets

• excellent fall color
• fairly rapid establishment and shade
• generally wet site tolerant (but periodic flooding, especially under other urban stress conditions, enhances the chance of this species contracting Verticillium Wilt)
• silvery bark on some young cultivars
• generally has symmetrical branching in youth

Liabilities

• alkaline soils usually cause leaf chlorosis and a weaker, slower growing tree
• shallow root system surfaces in youth or by mid-maturity
• somewhat prone to Verticillium Wilt and leaf scorch

Habitat

• zones 3 to 9
• native to Eastern North America

SELECTIONS

Alternates

• medium to large-sized shade trees (Acer platanoides, Acer saccharum, Fraxinus pennsylvanica, Gleditsia triacanthos, Tilia cordata, Tilia tomentosa, Zelkova serrata, etc.)
• excellent bright red fall color found in trees (Acer palmatum [green-foliaged, non-cutleaf, upright forms], Nyssa sylvatica, Oxydendrum arboreum, Quercus coccinea, etc.) or shrubs (Euonymus alatus, Rhus coppalina, Viburnum rufidulum, etc.)

Variants

• Acer rubrum 'October Glory' - actually holds its dark green foliage throughout October for most of the Eastern United States and becomes crimson red in early to mid-November, being one of the last shade trees to exhibit fall color; maturing at 50' tall by 35' wide
• Acer rubrum 'Red Sunset' (also known as 'Franksred') - red-orange fall color in September, defoliating and becoming dormant before most other shade trees, with bark that is smooth and a very light silvery-gray in youth, maturing at 50' tall by 35' wide

NOTES

Translation

• Acer is the Latin name for Maple.
• rubrum translates as "red", referring to the red fall color of many forms.

Purpose

• Red Maple is good shade tree with dependable red foliage in Autumn (among its selected cultivars).

Summary

• Acer rubrum is a common shade and Autumn accent tree in Eastern North America, also valued for its relatively quick growth, dense shade, and symmetry in youth.