Kathleen Cue, Nebraska Extension Horticulture Educator in Dodge County
Spring’s re-birth of all that is green is a good time to assess how trees and other landscape plants made it through winter. Many evergreen trees, such as spruce, are exhibiting signs of winter burn, with browning and bronzing of needles. Winter’s deep cold and strong winds dried out plant tissues, resulting in loss of evergreen needles and dieback of branches in deciduous trees. This dieback is a function of the tree’s survival mode, allowing needle loss and twig dieback so that the rest of the tree may survive.
Tasks tree owners can do to help trees, both evergreen and deciduous alike:
Water deeply and infrequently. For those with an irrigation system, it is likely the turfgrass is receiving adequate water, but trees are not. Most irrigation systems water shallowly and frequently, keeping upper soil layers saturated while the tree’s lower roots remain dry. Use a screwdriver to determine if water is reaching lower soil layers—one easily pushed into the soil indicates water is soaking in. Remember to do a deep soaking prior to ground freeze in the fall.
Mulch. A 2–4-inch layer of an organic mulch, such as shredded bark or wood chips, replicates what nature creates on the forest floor. Known as duff, this accumulation of twigs, leaves and other organic debris fosters rich microbial activity beneficial to tree roots. Landscape fabric, rubber tire mulch and rocks do not support microbial growth, keep root zones hotter, and do little to help trees.
Do not fertilize. If the lawn is regularly fertilized, then trees are receiving adequate nutrition for good health. Fertilizers injected into the soil and fertilizer spikes foster leaf growth in trees but force trees to neglect needed functions like root growth and pest resistance. Fertilizer spikes in particular burn roots, causing root dieback.
Prune trees to remove rubbing branches, hangers, and double leaders. These areas promote decay, making trees susceptible to damage from wind and snow loads. Never prune trees for the sole purpose of allowing in sunlight to grow better grass beneath. Thinning out tree canopies alters tree aerodynamics, increasing the potential for wind damage.
Remove some of the lawn. Turfgrass competes with trees, especially young trees, for water and nutrients. By removing grass to a distance four feet from the trunk, trees will grow faster and be healthier overall. Do not forget to follow up the grass removal with mulch.
Don’t forget the old trees. One common mistake is to believe old trees need no care at all. Foresters tell us that there is a five-year lag to tree stress, often not becoming apparent until trees are exhibiting noticeable symptoms, often too late to counter. This means 2020’s drought will negatively impact trees until 2025, increasing the likelihood for insect pests and disease problems to gain a foothold. While older trees have stronger, more developed roots to access water during dry spells, drought conditions mean lower sources of water in the soil are gone. Mulching and deep, infrequent watering are vital to older trees too.
Photo Above: Honey Locust Tree - Racek
Go to Dodge County Horticulture web page for more gardening information.