Q: I used Roundup in the rock mulch around my trees to kill the weeds and grass that were growing in the rocks. It worked, but as you can see by the photo, I have a ring of dead grass around the outside. I thought this only killed what it touched, but I was wrong. Can you recommend a product to use that will just kill what it touches in the rock bed? I used a 2-gallon pump-type sprayer.
A: The circle of dead grass at the outer edges of the targeted area is likely caused by the fine mist from the sprayer that drifted onto the surrounding grass. Glyphosate, which is the active ingredient in Roundup, does kill only what it touches, but in this case, it also touched the grass outside the target. This overspray is all too common, and shows the potency and danger of fine, almost invisible spray particles.
Super Concentrate Roundup is highly concentrated, as the name implies. The fine mist from concentrated glyphosate is enough to damage the grass on which it lands. Fine, invisible particles that land outside the targeted area easily cause dangerous overspray.
Spray drift and overspray can be reduced with a very coarse, low-pressure spray, or even a watering can that applies the Roundup with no pressure, which reduces or eliminates airborne droplets. Also, it's important to apply only enough Roundup to coat the leaves of your target weeds without adding excess, which could run off into the surrounding grass. I immediately recognized the problem, because I've done this same thing myself in the past.
Q: I was wondering if it's possible to get my clematis to bloom again this year. It’s sad to see it done blooming already. — Robin Olson.
A: Yes, it is sad to see clematis finished flowering. Clematis will often give a small rebloom in September, smaller than the summertime flush of blossoms, but still nice.
This can be encouraged by fertilizing now. Although fertilizing trees and shrubs is discouraged after July 1 because it can cause a flush of growth that doesn’t have sufficient time to toughen up before winter, most clematis varieties, including the blue/purple Jackmann, die back to near ground level anyway. Fertilizing clematis again can encourage a flush of new growth capable of later bloom.
Miracle-Gro fertilizer can be applied to the soil around the clematis. I would apply about 3 gallons of the fertilizer solution, slowly poured onto the root system. Miracle-Gro can also be sprayed onto the clematis foliage, which is handy if you have a Miracle-Gro hose-end feeder. Fertilizer is also absorbed through the leaves of plants, along with the roots.
Q: I have a bad case of powdery mildew on my ninebark. I've never had this issue on anything previously. What do I do to get rid of it? — Evelyn Bymoen Karpinen.
A: Powdery mildew is a fungal disease, and ninebarks, lilacs and peony foliage are all very susceptible. Once the foliage is affected, the gray/white coating on the leaves is nearly impossible to remove.
The best remedy is to apply fungicides, such as those containing the active ingredient chlorothalonil, as preventatives at the very earliest sign of the disease. Powdery mildew fungi love humidity, so pruning to allow better airflow can help. Avoiding watering the foliage can help reduce the localized humidity also. Raking the leaves in the fall and practicing good sanitation may also help, although the powdery mildew spores are ubiquitous, a wonderful word I learned in microbiology meaning "all over the place."
If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at firstname.lastname@example.org or call 701-241-5707. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.