The Free Press, Mankato, MN

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October 23, 2013

Act now to promote long-term tree health

Drought conditions over the last two-plus years have left trees and other perennial plants visibly stressed this fall. Tree stress symptoms include abundant seed production, leaf scorch, early fall colors, leaf drop, limb die-back and yellowing or browning of leaves and needles.

Fortunately, several measures can help enhance tree and shrub health.

Trees and shrubs — especially conifers (such as pine, spruce and cedar) and those planted in the last three years — should be watered generously until the soil freezes. Mulching newly planted trees also helps reduce winter root damage.

Young maples and thin-barked trees may benefit from sunscald protection to prevent the bark from cracking this winter and spring. This usually involves plastic tubes or tree wraps, which are removed in spring. These practices can also help reduce winter animal damage.

Deciduous trees and shrubs can incur shoot die-back and bud death during the winter. Flower buds are more susceptible to injury than vegetative buds. A good example of this is forsythia, where plant stems and leaf buds are hardy, but flower buds are very susceptible to cold-temperature injury.

Die-back: Little can be done to protect trees and shrubs from winter die-back. Plants that are marginally hardy should be planted in sheltered locations (microclimates). Plants in a vigorous growing condition late in the fall are most likely to suffer winter die-back, so avoid late-summer pruning, fertilizing, and overwatering. Fertilize in the spring on sandy soil or in the fall on heavy soil after the leaves have dropped.

Root Injury: Roots do not become dormant in the winter as quickly as stems, branches and buds, and roots are less hardy than stems. Roots of most trees and shrubs that grow in Minnesota are killed at temperatures at or below 0-10 degrees. These plants survive in Minnesota because soil temperatures normally are much higher than air temperatures and because soil cools down much more slowly than air temperature. Snow cover and mulch act as insulators and keep soil temperatures higher. With newly planted trees, cracks in the planting hole backfill will allow cold air to penetrate into the root zone, reducing fall root growth or killing newly formed roots.

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