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FIELDING QUESTIONS: Wait to trim ornamental grass until next spring

Ornamental grasses winter best with the tops left intact, without cutting back in the fall. Special to Forum News Service1 / 2
Don Kinzler, Growing Together gardening columnist for The ForumMichael Vosburg / Forum Photo Editor2 / 2

Q: We've got several plants of Karl Foerster ornamental grass in our landscape. Should they be cut back in the fall? — Bob Larson, Bismarck.

A: Ornamental grasses winter best with their tops left intact, without cutting back in the fall. The tops catch snow, which provides good insulation against frigid cold. Many of these ornamental grasses have decorative seed heads that add interest to winter landscapes and attract birds to nibble seed.

Grasses, like the commonly planted Karl Foerster, are best cut back in spring to a few inches above ground level, before new grass shoots begin emerging from the crown.

Q: As I was mowing our lawn this past summer, I noticed my shoes and the lawnmower were both covered with a fine rust-colored powder from the grass. The lawn looks fine, but should I be concerned about a disease? — D. Jorgenson, Fargo.

A: The rusty, orange powder is composed of millions of spores of rust fungi. Although it's considered a disease, it's usually more of an annoyance than actually causing harm to lawngrass. Our lawn was rusty also this year. When the right conditions of weather, moisture and fungal organisms align, the rust develops, often in mid- to late-summer.

Most sources don't recommend fungicide treatment to prevent or treat rust on home lawns. Although there are a few references to lawns being weakened by the rust, most research considers lawn rust a cosmetic nuisance. On our own lawns, I've never felt rust caused diminished grass growth. Although we can't control the weather (heavy evening dews that exacerbates fungi growth), we can help by avoiding evening and nighttime watering of lawns, and water in early morning instead.

Q: The leaves on the hybrid tea roses I planted this summer are still clinging to the rose bush, even after several hard freezes. I'd like to cover them for the winter, but can I do that when there are still leaves on the bush? — Mary H., Fergus Falls, Minnesota.

A: Many rose bush varieties, including most hybrid tea types, tend to hold their frozen leaves, rather than dropping them in autumn. Sometimes they'll cling on the bush all winter until new growth pushes the old off. This wouldn't be a problem, except when tender roses are covered with a winter insulation of leaves, straw or woodchips, the clinging foliage can develop mold.

Before covering for the winter in early November, many rose growers first strip the leaves from their rose bushes by running their hands along each cane. Others apply fungicide to the foliage to control rot before covering.

Q: I cut my peony down to the ground in August because it was unattractive. My neighbor said I did it too soon, and should have waited until fall. Any opinions? — Barb S., Grand Forks.

A: Peonies are one of the few perennials that are best cut down in fall, rather than waiting until spring. Because perennials are moving food internally from the foliage down into the roots in late summer in preparation for winter, delaying cutback until after hard freezes is best for the plant.