Ask the Master Gardener: Ornamental grass is easy to maintain and aesthetically pleasing

Dear Master Gardener: I would like to plant a row of tall ornamental grasses along a curve in my driveway. What do you recommend?

Answer: Ornamental grasses are low maintenance, easy to grow, increase rapidly, typically disease and insect free, and aesthetically pleasing. What’s not to like? Most ornamental grasses grow best in full sun and many of them do well in open, exposed areas where other perennials would be damaged by gusts of wind. They add beauty, form, and texture in the winter landscape, so don’t cut them down to the ground until spring.

Here are some recommendations:

• Feather reed grass (Calamagrostis) is a fantastic cool-season grass that makes an excellent vertical accent plant. It is hardy to zone 3. You see it a lot in commercial landscapes because it grows well in many soil types. Avalanche, Eldorado, Overdam,  and the very popular Karl Foerster reach 60 inches in height with a width of 18-24 inches at maturity. 
• Calamagrostis brachytricha is a Korean fall-blooming reed grass that is hardy to zone 4, but has been thriving in my Brainerd area garden for years. This is one of the few ornamental grasses that will tolerate some light shade, but prefers full sun. Korean feather reed grass reaches 48 inches in height and produces 12-inch plumes with a pinkish-purple tinge in August. 
• Little Bluestem (Schizachyrium scoparium) is a zone 3, warm-season prairie grass that forms a dense clump. Blue Heaven was developed by the University of Minnesota and released in 2008. It gets 40-48 inches tall and 25-30 inches wide. It has stunning fall color. The foliage is dark blue to burgundy in the summer, then turns red and purple in the fall. This grass needs good soil drainage to flourish. 
• Golden Sunset-Yellow Prairie Grass (Sorghastrum nutans) is another University of Minnesota ornamental grass released in 2020. It looks similar to Karl Foerster feather reed grass and is hardy to zone 3. Its tall, upright form (48-72 inches tall at maturity) doesn’t fall over and it gets 36 inches wide. This grass features olive-green foliage with numerous yellow and golden-bronze flowers.

Dear Master Gardener: I bought some potatoes and when I cut them in half to boil there was a star-shaped opening in the middle with some brown discoloration around it. Can you still eat them?

Answer: Not only will you find this phenomenon in potatoes purchased in a store or farmer’s market, but gardeners also discover it from the potatoes grown in their vegetable garden. This star or lens-shaped cavity in the inside of the potato is called hollow heart. According to the U.S. Department of Agriculture, “It appears to be caused by an abrupt change in tuber growth rate which usually occurs after a period of stress.” We have experienced abrupt changes in growing conditions this summer with drought, then an abundance of rain. Some research has shown that if the hollow heart has brown edges, then it happened early in the potato’s growth and those that are not darkened happened closer to the potato’s harvest. For those gardeners growing potatoes in their vegetable gardens, it is very important to keep the soil moist during dry periods. Yes, you can still eat them. Hollow heart doesn’t affect the taste, quality or nutrition of the potatoes.

Dear Master Gardener: Should Astilbe be deadheaded?

Answer: Deadheading Astilbe is a matter of aesthetics. If the brown flower head bothers you, cut off the flower down to the first set of leaves. If that doesn’t look good, cut it off further down the stem to the next set of leaves. Removing the spent flower heads will not extend or promote more flowers.

Dear Master Gardener: I have a magnolia tree at my home in Minneapolis. There are lots of dome-shaped bumps that are pinkish-orange to brown in color on the branches. I’m not sure if it’s possible, but they seem to be attracting wasps. What are they and what should I do?

Answer: It sounds like you have magnolia scale, an insect problem typically seen in late July and early August when the nymphs mature. The honeydew that is created by the scales attracts ants, wasps, and other insects. According to the U of M, magnolia scale populations can build rapidly within one generation. Pesticide treatments should be made the same season they are observed on the plant. Apply horticultural oils in late fall and early spring to smother the overwintering nymphs. In addition, apply a systemic insecticide in the spring.

Dear Master Gardener: My coneflower plants have weird-looking, deformed flowers. Is this some kind of disease?

Answer: Unfortunately, it sounds like your coneflowers have a disease called aster yellows. Aster yellows tends to be more prevalent during hot years, which explains why you are experiencing it this year. It spreads by leaf hoppers, so you will need to remove the infected plants right away. If some of your plants are not showing symptoms, you don’t have to remove them, but keep an eye on them. Remove any that start showing symptoms. Do not put infected plants in your compost.

You may get your garden questions answered by calling the new Master Gardener Help Line at 218-824-1068 and leaving a message. A Master Gardener will return your call. Or, emailing me at umnmastergardener@gmail.com and I will answer you in the column if space allows.

University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. Information given in this column is based on university research.