Non-hardy shrubs might look nice, but they'll probably die back eventually
"Fielding Questions" columnist Don Kinzler explains why boxwood shrubs tend to not do well around here and also offers advice on sourcing wildflower seed and fertilizing roses.
Q: What is happening to these shrubs in our yard? We moved into this home three years ago and the shrubs were green, but have since begun turning yellow. We trimmed out the yellow a year ago but they’re doing the same again. Could the damage be from lawn fertilizer or Trimec weed killer? — Mike and Nan B.
A: The shrub in the photo is boxwood, and many varieties sold, especially at national chain stores, are extremely marginal in adaptation for our area. Boxwood is a "broadleaf evergreen," meaning the shrubs retain their rounded green leaves all winter. The many non-adapted varieties sold have difficulty surviving long term in our region, frequently suffering severe winter burn, which is the most likely case in the photo. They might grow for a season or two, and then die back severely during a rough winter.
The North Dakota Department of Agriculture, in their non-hardy woody plant list, officially designates most boxwood hybrids and cultivars as non-hardy for the state. An exception is made for the cultivars Green Velvet, Green Mound, Calgary, Saskatoon, Northern Charm and Green Ice.
Although those cultivars could be tried, I haven’t seen widespread success with boxwoods in North Dakota and have seen very few reach a ripe old age. In a sheltered microclimate, protected from winter winds and receiving deep insulating snow, success is more likely. In a typical North Dakota landscape, boxwood can be a disappointment.
Although non-adaptability is the main problem with boxwood, Trimec weed killer contains ingredients that can definitely injure shrubs if the spray drifts onto the foliage. Dicamba, which is an active ingredient in Trimec, can also move downward in the soil, seriously injuring trees and shrubs as their roots absorb the chemical.
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Q: I have an area at the lake that’s on a slope, and I’d like to seed wildflowers for bank retention and beauty. In past years on other properties, I’ve bought wildflower seed from American Meadows and was satisfied, but it’s very expensive. Is the seed quality from such sources better than the wildflower seed from places like Menards? Are there local sources of good seed? — Ryan M.
A: Wildflower seed is best purchased from sources originating in the North, whose mixes contain flower types suited to our Northern growing conditions. Prairie Restorations , in Princeton, Minn., is well-known for their wildflower products. Agassiz Seed , headquartered in West Fargo, also lists wildflower seed in its product line.
Q: Should I be fertilizing roses now? I covered them last winter, but only one out of six roses appear to be starting growth. — Jerry A.
A: Many roses around the region suffered major cane dieback this winter, probably due to the lack of deep, insulating snow. Even when we cover roses in the fall for winter protection, generous snow over the surrounding soil provides important extra insulation.
Most roses that I’ve observed this spring are already beginning growth, if they’re alive. Prune damaged canes down to the point of new sprouts. Roses that show no sign of growth by late May likely didn’t survive.
Fertilizing roses is important to provide nutrition for vigorous branch growth and plentiful flower buds. Start fertilizing now in May, and continue through June and early July. Then discontinue, which lets the rose bushes utilize the existing nutrition and slowly begin toughening up for the approaching fall and winter.
Several types of fertilizer will work fine. Some are formulated specially for roses. All-purpose granular 10-10-10 provides well-balanced nutrition. Water-soluble Miracle-Gro types are good. Organic fertilizers are another option. Follow label directions for amounts.
If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at email@example.com. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.