Q: I notice a light brown grass growing through my lawn. I did some checking on the Internet, and I think I have nimblewill. What chemicals can you recommend to control this weed?
A: Nimblewill is a common weed of lawn areas. It often goes unnoticed during the summer, but turns brown and stays that way with the onset of cold temperatures. Because nimblewill is a grass, it is difficult to control in the lawn. Small areas can be killed with a non-selective herbicide, but the grass will be killed as well, so the area will have to be reseeded or replaced with sod. Larger infestations may call for lawn renovation.
Q: Can you tell me more about tiarellas? My friend grows them in her garden, and I think they’re lovely.
A: This native perennial, also known as foamflower, deserves a place in every shade garden for its decorative foliage and foamy spikes of creamy white flowers in spring.
Many cultivars of Tiarella cordifolia are available featuring prolific bloom and striking leaf shapes and colors, including ‘Spring Symphony,’ ‘Black Velvet,’ and ‘Iron Butterfly.’ Tiarellas perform best in shady sites with rich, moist but well-drained soil.
Q: What causes the leaves on my boxwood to cup and curl? This happens every spring.
A: Boxwood leaves are damaged by the boxwood psyllid. This insect pest, related to the aphid, damages boxwood shrubs by sucking leaf sap and distorting leaf tissue. The psyllids hatch in spring and begin to feed on leaf tissue. As the leaves expand and begin to cup, they surround and protect the psyllids. In summer, adult psyllids lay overwintering eggs near bud scales.
Cupping damage on the boxwood leaves cannot be reversed, but it is only cosmetic. For heavy infestations or key plants, a systemic insecticide with the active ingredient imidacloprid can be applied in fall to prevent damage next spring.
Q: I love the look of the weed called mullein — its wooly leaves and tall flower spike have an interesting texture and structure. If I grow the weed on purpose in the garden, what should I do to make sure it doesn’t get out of hand?
A: You’re not the first gardener to want to grow this weed. Mullein is a biennial, so controlling its spread is fairly easy so long as you’re prepared to selectively remove seedlings. In its first year of growth, mullein produces a low rosette of fuzzy leaves. In its second year, the tall flower spike is produced, which matures to produce thousands of small seeds; this original plant dies.
To manage the spread of mullein, you can remove the flower stalk after the flowers have faded, mulch around the base to prevent the growth of seedlings, and remove all but a few seedlings in subsequent years.
Interestingly, this plant has had many traditional uses over the centuries. It was originally brought to North America in the 1700s for use as a fish poison; the leaves contain rotenone. While Europeans and later colonists used mullein for medicinal uses, this practice is not advised because in addition to the poison rotenone, the leaves also contain coumarin, a toxin used in rat poison.
Q: I have a small patch of woods behind my house that has a lovely assortment of spring wildflowers. In recent springs, I’ve noticed garlic mustard growing in the woods. Do I need to worry? I see lots of garlic mustard in our parks as well.
A:. This invasive plant has become a widespread problem in natural areas in the last few decades. Garlic mustard was originally brought to North America for its culinary uses; the leaves are high in vitamins A and C. In recent years, the plant hopped from the garden into woodland areas, where it readily forms dense colonies. These colonies out-compete native plants for space and light, making garlic mustard a threat to many woodland wildflowers. Chemicals produced by the plant can also inhibit the growth of non-garlic mustard seeds.
Garlic mustard pulls — organized sessions where volunteers pull up garlic mustard plants — are less common then they used to be. Soil is disturbed when the plants are pulled, creating an ideal disturbance where new garlic mustard plants will grow. Plants in flower are readily able to produce mature seeds even after pulling, meaning plants have to be bagged and sent to a landfill.
Many natural resource managers now use winter applications of the herbicide glyphosate to manage stands of garlic mustard.
This practice kills the weed but has no effect on native wildflowers. Since soil is not disturbed, fewer garlic mustard seedlings regenerate, and less waste is created.
In your wooded area, you could selectively apply glyphosate to garlic mustard plants in winter, or cut off flower stalks before they go to seed.
With persistence, you should be able to reduce the garlic mustard population in your woods without disturbing the wildflowers.
Q: I have wild onion coming up in a few of my flowerbeds. How can I control this plant? Can I eat it?
A: Eating your enemy (when it’s a weed) is sometimes a good solution, but not in the case of wild onion. This plant is toxic to humans and livestock, so don’t mix it into salads or vegetable dip. Wild garlic, a close cousin to wild onion is not toxic. To distinguish the two, look at the leaves in cross section. Wild onion has flat leaves in cross section; wild garlic is round and hollow.
Both weeds are difficult to control, since bulbs can be deep and may be missed when pulling or digging. The non-selective herbicide glyphosate will kill wild onion and wild garlic, but repeat applications may be necessary.
Denise Ellsworth directs the honeybee and native pollinator education program for the Ohio State University. If you have questions about caring for your garden, contact her at 330-263-3700 or click on the Ask Denise link on her blog at www.osugarden.com.