Q: Can you identify the plant in the photo? My daughter-in-law has it, along with a pink one. It’s considered an old-fashioned plant, and it only flowers in the fall. - Debbie O.
A: The tremendous autumn-blooming perennial in the photo is commonly known as a fall aster. These winter-hardy perennials are vastly underused, and thankfully are receiving increased recognition as important additions to perennial flowerbeds. Like you mentioned, they are an old-fashioned perennial, but as relevant today as ever.
Much good can be said about fall asters. They bloom abundantly in autumn when many other flowers have lost steam. They’re a good pollen source for bees and other beneficial insects when fewer plants are flowering. Fall asters are winter hardy in Zones 3 and 4, and grow more prolifically than mums, many varieties of which are borderline in survivability.
Common older varieties include Purple Dome and Alma Potschke pink. Newer cultivars have been developed that are often more compact and bushier including October Skies, Bluebird, Wood’s Blue and Crimson Brocade. Locally-owned garden centers are a good source of selection.
During summers with high heat and humidity, mildew can cause foliage decline. If such weather is anticipated, treat preemptively with an all-purpose flower fungicide, and avoid wetting foliage while watering.
Q: I’m trying your suggestions for keeping geraniums over the winter. I cut them back to about 3 inches in mid-September, repotted them and put them under lights for 16 hours a day in a garage that is heated to 60 degrees. They are growing like weeds, and at this rate, I'll be able to decorate them as Christmas trees in 6 weeks! I reduced the light length to 12 hours yesterday. Are there any other ways to slow them down? - Karen H.
A: Because they’re growing well, you’re doing everything right and congratulations are in order. I should mention, though, that this method that I’ve used successfully for years is intended to keep the geraniums growing nicely during winter. It’s not a method for slowing the geraniums, or letting them go dormant, which is a separate method used by some.
I’d continue using 16 hours of light per day, which is the standard for growing plants under lights, instead of a reduction. Geraniums love cool temperatures, so they’ll thrive at 60 degrees. Geraniums prefer being kept on the dry side, so space watering frequency accordingly.
It’s great the geraniums are growing profusely, so I wouldn’t try to slow them down. Instead, keep them growing well, and then on March 1 trim back the winter’s growth, which will stimulate fresh, well-branched, beautiful, compact plants ready to go outside by mid-May.
Q: I received a beautiful hibiscus tree for Mother’s Day and it bloomed all summer. Unfortunately, I brought in a potted tomato plant from our deck on a cool night and it passed whiteflies onto the hibiscus. I’ve sprayed it with water and treated it with garden dust. There is no longer a cloud of flies when the leaves are touched, but two or three still remain, and I don’t know what to do, as it’s losing a lot of leaves. Any suggestions? - Diane J.
A: Hibiscus can be insect-prone, often attacked by whiteflies, spider mites, mealy bugs and aphids, so you aren't alone in your battle to keep the hibiscus healthy.
Two indoor-friendly products for treating these insects are insecticidal soap and neem oil, available at garden centers. Thoroughly saturate both upper and lower sides of leaves, following label instructions. This can be a messy operation best tackled in a bathroom shower or other protected area.
Following spraying, applying systemic insecticide granules to the soil would be wise. Systemics are taken up by the plant’s roots and protect the plant from the inside out, as insects suck plant sap. Houseplant systemic insecticides are available at many garden centers.
Yellowing of hibiscus leaves is quite natural in the change from summer to fall, and as the plant transitions from outdoors to indoors. If the insects are brought under control, the hibiscus will develop new growth as it adjusts and recovers. In the meantime, be certain not to keep the soil too moist, but allow to dry well between waterings.
If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at firstname.lastname@example.org. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.