Whats Up in the Garden by Jackie Dohlman, Master Gardener

Tips on Snow Molds, Pruning Butterfly Bush, and Dividing Rhubarb Plants

Areas of my lawn that were covered with snow for most of the winter aren’t greening up. What could be wrong?

Snow molds may be responsible for the brown spots in your lawn. Two snow mold diseases, gray snow mold and pink snow mold, occur in Iowa. Gray snow mold is caused by two species of the fungus Typhula, while pink snow mold is caused by the fungus Microdochium nivale.

Symptoms of snow molds first appear when snow melts in late winter or early spring. Circular, straw-colored patches appear in the lawn as the snow recedes. Patches caused by gray snow mold may be a few inches to a few feet in diameter, while those caused by pink snow mold tend to be smaller, less than six inches across. These patches may continue to enlarge if the grass remains cool and wet. Grass in the patch may be matted and wet, with pink or gray colored fungal growth over the patch or on the edge. Gray snow mold causes small, pinhead-sized, round structures (sclerotia) to develop on the leaves and crowns of the grass plants.

Damage caused by snow molds is usually not serious. Affected areas typically green up, though more slowly than the rest of the lawn. Gently raking the affected areas may help to dry them out and prevent further fungal growth. In future years, problems with snow molds can be minimized by avoiding excessive nitrogen fertilization in fall, keeping the grass mowed until growth stops in fall, raking fallen leaves, and by not throwing or piling snow on problem areas. Affected areas will need to be overseeded if they fail to green up.

How should I prune my butterfly bush in spring?
The butterfly bush (Buddleia davidii) is actually a medium-sized, woody shrub. However, it’s often regarded as a herbaceous perennial in Iowa because the plant typically dies back to the ground each winter. In late winter/early spring, prune the butterfly bush back to within a few inches of the ground. The butterfly bush grows back rapidly after the dead wood is removed and blooms on the current year’s growth. The 6- to 12-inch-long flower spikes may be white, yellow, pink, blue, violet, or purple. By the end of summer, plants are often 5 to 6 feet tall.

When can I divide my rhubarb plants?
Early spring is the best time to divide rhubarb plants. Dig up plants as soon as the ground can be worked in spring. Divide each plant into sections with a large knife or spade. Each section should have at least two to three buds or shoots and a large section of the root system. Replant immediately. Set the divided sections in the ground at the same depth as they grew previously. Water thoroughly. Continue to water the plants on a weekly basis (during dry weather) through the remainder of the growing season.

Got gardening questions? Contact the Hortline at (515) 294-3108 (Monday - Friday; 10 a.m. -12 noon and 1 - 4:30 p.m.) or send an e-mail to hortline@iastate.edu. For more gardening information visit us at Yard and Garden Online at http://www.yardandgarden.extension.iastate.edu/

photo courtesy of Miss Chien at flickr.com