Ornamental trees add dimension to the landscape in every season, with spring or summer flowers, spectacular fall color, and interesting winter textures.

Only at the U

The University's Plant Hardiness Laboratory is internationally known for cold hardiness studies. The concept of "Deep Supercooling" originated here in the 1960s to explain how--at the cellular level--plants survive winter. Extremely cold temperatures are not the only hardiness factor; the initial work was understanding the basic physiology of cold hardiness and how plants acclimate for winter and deacclimate in the spring.

The acclimation process is triggered late in the growing season as days shorten and temperatures fall. Those environmental cues prompt changes in the plant that result in greater cold tolerance. When water in any tissue turns to ice the cells die; a plant that is slow to acclimate will be injured or killed by an early cold snap. But learning that cellular water in buds can stay liquid until ­40 degrees F. led to understanding why and how some plants survive.

Mid-winter hardiness and the rates at which acclimation and deacclimation occur for a particular species can vary from year to year. Laboratory freezing tests plotted for various fluctuations help researchers determine a cultivar's ability to withstand harsh winter conditions. The desired result? Hardy plants for Minnesota.

Maples

Only from the U

'Firefall' (TM) Freeman maple, the newest tree release from the University, is the result of a cross between 'Beebe,' a cut-leaf silver maple, and an earlier U of M red maple introduction, 'Autumn Spire.' Field trials began in 1992, with young trees evaluated for form, cold tolerance, and quality and timing of autumn leaf coloration. The initial selections were clonally propagated by softwood cuttings in 1994 and distributed to cooperators in Iowa, Oregon, Manitoba, and outstate Minnesota.

Flowering Crab

Buckeye

Flowering Plum

Amur Maackia

Redbud

Corktree

Kentucky Coffee Tree

Jack Pine