FirefallTM Freeman Maple

Steve McNamara, Kathy Zuzek, Nancy Rose, Harold Pellett, and Stan C. Hokanson
University of Minnesota Department of Horticultural Science, St. Paul, MN

Introduction
Freeman maples (Acer x freemani E. Murray) are interspecific hybrids of red maple (Acer rubrum L.) and silver maple (Acer saccharinum L.) (Bachtell, 1988; Freeman, 1941). Cultivars of Freeman maple that purportedly combine the attractive form, flowers, and foliar characteristics of superior red maple genotypes with the faster growth rate and broader environmental adaptability of silver maple are becoming increasingly popular as landscape trees (Bachtell, 1988). However, when planted in USDA zone 4a (United States National Arboretum, 2003), many of the commercially available cultivars of Freeman maple fail to develop an attractive fall foliage display prior to the occurrence of a killing frost. A breeding program was initiated at the University of Minnesota in 1990 to create better performing Freeman maples for northern climates. This poster describes a new Freeman maple cultivar named FirefallTM (‘UMNAF#1’) resulting from this effort.

Origin
Controlled pollinations were made at the University of Minnesota Landscape Arboretum in Chanhassen, Minnesota in April 1990 between ‘Beebe’, a cut-leaf form of silver maple (the female parent) and ‘Autumn Spire’ red maple (the male parent), an earlier University of Minnesota introduction that originated near Grand Rapids, Minnesota in USDA zone 3b (McNamara and Pellett, 1993). Progeny resulting from this cross were grown out in Chanhassen and evaluated for form, cold tolerance, and quality and timing of autumn leaf coloration. Ramets of advanced selections were distributed to cooperators in Iowa, Minnesota, Oregon, and Manitoba, Canada. The cultivar ‘UMNAF #1’ was selected for its cold hardiness, symmetrical form, seedlessness, and consistently early and attractive fall color display. The cultivar was trademarked FirefallTM and officially released to wholesale nurseries in 2001.

Description
FirefallTM has an upright oval form with a strong central leader (Fig. 1). Branches ascend from the main trunk at an average angle of approximately 50 degrees. The trunk and main branches are light gray (RHS 201D) (Royal Horticultural Society, 1995). Staminate flowers with reddish-brown (RHS 53B) anthers typically emerge in early to mid-April in Chanhassen. To date, neither female flowers or seed have been observed on the original tree or clonally propagated specimens of this cultivar.

Leaf shape is variable but is typically intermediate to those of the parents. Mature leaves have three main lobes with two smaller, subtending lobes, a rounded to acute base, doubly-serrate margins and palmate venation. Sinuses are irregular, ranging from lobed to cleft. In summer, the adaxial leaf surface is medium green (RHS 147A) and glabrous and the abaxial surface is silver green (RHS 191B) and glabrous. Peak autumn foliage color is predominantly red (RHS 180A), ranging from RHS 44A to RHS 179B (Fig. 1).

Performance
FirefallTM is well adapted to northern climates. Results of controlled laboratory freezing tests indicate that FirefallTM cold acclimates earlier in the fall, develops greater midwinter hardiness, and deacclimates later in the spring than a number of other red and Freeman cultivars in Chanhassen (Table 1). It is completely cold hardy in USDA Zone 4 and appears to be suitable for use in portions of Zone 3. Some twig dieback was reported on young trees growing in a field production nursery in Portage la Prairie, Manitoba, USDA Zone 3b, (Rick Jurand, Jeffries Nursery; personal communication).

FirefallTM has consistently developed an attractive fall foliage display (Fig. 1) in late September or early October in Chanhassen, MN, 1-3 weeks before other Freeman maple cultivars. The early coloration of FirefallTM is advantageous because it is more likely than other cultivars to produce an attractive display before the occurrence of a killing frost. The cultivar has also colored well in Oregon and Iowa. However, based upon the performance of other cultivars of northern provenance (Sibley et al., 1995), FirefallTM may not color well in the southern United States.

This cultivar exhibits a moderately rapid growth rate. In Chanhassen, the average height of eleven-year-old trees produced from softwood cuttings was 9.4 m with a trunk diameter at breast height (1.37 m above the ground) of 13.0 cm. FirefallTM grows best in full sun on moist, well-drained, slightly acidic soils, but is fairly tolerant of wet and dry soils with pHs as high as 7.3. The cultivar’s ability to tolerate more alkaline soil conditions is unknown.

The cultivar can be used as a specimen shade tree for residential lawns, parks, golf courses, and commercial landscapes. Due to its large mature size, it is not suitable for use in narrow sidewalk plantings or under power lines. Combining excellent cold hardiness, early fall coloration, a symmetrical form, and seedlessness, FirefallTM should prove to be a valuable new landscape tree for northern gardeners.

Propagation and Availability
FirefallTM can be propagated from softwood cuttings collected in early summer (June in central Minnesota), treated with a 5-second quick dip in 8000 mg-L-1 indolebutyric acid in 50% ethanol, stuck in a 2:1 (v/v) mixture of coarse perlite and peat moss and placed under intermittent mist at air temperatures of 22 - 27 C. Cuttings typically root within 5-8 weeks.

The University of Minnesota trademarked the name FirefallTM for this cultivar in 2001 and applied for a plant patent in 2003. The cultivar was officially released to licensed wholesale nurseries in 2001 and will be commercially available from several wholesale nurseries in 2005.

Literature cited

Fig. 1. Three eight-year-old ‘FirefallTM’ Freeman maples grown in Chanhassen, MN