Q: The soil in the location to which we recently moved is heavy clay. I brought some rhubarb along to plant, but the photo is what my rhubarb looks like since planting it here in May. I have watered it often but the leaves are beginning to yellow and it has grown very little. Should I dig it up in the fall (if it lives that long) and build a raised bed for it? What could be wrong with it? - Nancy P.
A: It's been a tough year for rhubarb, which prefers weather that's cool and moist instead of hot and dry. There are several recommendations for getting the rhubarb back into good health. Because there are signs of leaf-feeding insects, apply a general-purpose insecticide such as Sevin, Permethrin, or Spinosad, following label directions, to reduce the holes in future leaves.
There are several fungal diseases that cause yellowing, spotted leaves. To prevent foliage diseases, apply a vegetable fungicide containing the active ingredient chlorothalonil to the leaves and stems. When watering, wet only the soil, keeping the leaves dry and preventing soil-borne organisms from splashing onto the leaves.
Rhubarb is a "heavy feeder" which means it responds well to generous fertilizer, which can be granular 10-10-10 or a water-soluble type like Miracle Gro. That will help build energy for the plant. Generally it's best to halt rhubarb harvest in early July, to let the plants spend the rest of the growing season building energy supplies for next year. A light harvest can be done in fall.
Rhubarb would prefer a less heavy clay soil. To help, work compost or peatmoss into the soil around the rhubarb, incorporating at least a two-to-three-inch layer into the soil around each plant.
To help rhubarb roots stay cool and moist, add a layer of mulch around each plant in a three-to-five-feet diameter circle. You can use grass clippings that haven't been treated with herbicides or shredded bark or similar material.
Q: I enjoy listening to you on WDAY Radio’s Jay Thomas show. Did I hear right the other day when you said it is OK to spray flowers with cool water when the sun is shining and it’s hot out to cool them down and minimize wilting? - Todd B.
A: Under normal conditions, a person doesn't usually spray down plants or flowers with water during the middle of the day, but on excessively hot days, such as over 90 degrees, many flowers and plants wilt easily and can become stressed to the point of going downhill. Most plants have an upper temperature threshold at which they begin to regress.
Spraying plants with cool water on excessively hot days is an emergency way to prevent permanent damage. The water’s coolness lowers the temperature of the leaves, and provides cooling by evaporation.
I've used this technique quite a bit this year, both on flower plants and on vegetables such as squash and pumpkins that have large leaves and wilt easily in heat, especially when the weather is dry.
Wetting leaves does increase the chances of foliage disease, so it's not a good idea to wet down the leaves when temperatures are merely warm. But on excessive, dangerously hot days, spraying plants with water can provide emergency relief.
Q: Are there any herbicides that I can use that are organic, that will kill weeds without being a danger to pets and animals? - Karen B.
A: An online search will provide a list of herbicides marketed as containing organic compounds such as vinegar. It’s important to remember, though, that none of the organic herbicides are selective. These products, such as those with vinegar as a base, will kill or damage all plants, both desirable and those classified as weeds, if contact is made.
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