The Free Press, Mankato, MN


June 11, 2014

Harsh winter to blame for lack of redbud bloom

Minnesota strains of non-native tree succumbed to cold temps

In many parts of the state, the past winter was the coldest in either 35 or 78 years, and it is a winter that will be remembered for long, persistent periods of very cold temperatures.

The persistent cold allowed deeper-than-normal frost penetration in soils even though snowfall was heavy and just as persistent as the cold temperatures. No matter what statistics you look at — lowest temperatures recorded in the state, average monthly temperature, number of days Minnesota reported the coldest temperature in the nation, amount and persistence of snow cover, soil frost depth, windchill conditions, number of nights with 0 degrees or lower — they all add up to one long, cold, snowy, difficult-to-live-through winter.

The past winter also took its toll on trees and shrubs — including eastern redbuds. Winter burn on evergreens and salt damage on roadside white pines were severe. With the arrival of spring, cold injury to plants that are marginally hardy in Minnesota showed up. Vegetative damage can be seen in most of the repeat-blooming shrub roses whose canes died back to the ground. These plants are now busy sending up new canes from their crowns. Because repeat-blooming roses produce flower buds on this year's canes, these plants will still be able to bloom throughout the summer.

Winter injury to flower buds occurred among other plant species. Among marginally hardy plants that have been introduced to Minnesota from warmer climates, flower buds are often less hardy than vegetative parts such as leaf buds and stems. An example of this type of injury from the past winter is being seen on eastern redbud (Cercis canadensis).

Eastern redbuds are small trees with lavender pink, pea-like flowers that open to cover tree canopies in May before heart-shaped leaves expand. Flower buds formed during the growing season of 2013 should have provided us with beautiful bloom this spring. Some redbuds in the heart of the Minneapolis/St. Paul area did bloom. But thanks to our low winter temperatures, the more common scenario, especially in suburbs surrounding the Twin Cities and in colder outstate locations, was flower bud mortality and lack of bloom.

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