Q: I have a virus on all my Knock Out roses and have been told by a nursery to dig up and burn them. I also was told to not plant roses in that spot again. What plants can I use to replace the roses? — Mahala Moore, Colbert
A: There's no good answer. Knock Out rose is unique in its continuous bloom habit and year-round interest. I asked a couple of local designers and they recommended butterfly bush, dwarf crape myrtle, 'Sonic Bloom Red' weigelia, Salvia greggii, 'Little Lime' hydrangea, 'Preziosa' hydrangea, 'Crimson Fire' loropetalum, 'Color Guard' yucca, compact nandina and dwarf abelia. None of these flower continuously like Knock Out rose, but I can visualize several combinations that would be interesting to view all year long.
Q: We make yogurt and strain it down to a half-gallon of Greek yogurt and a half-gallon of whey. We have read that whey can be used to help tomato plants, but I'm not sure what that might do to the soil. — Clifton Woodall, email
A: I don't think small amounts of unsalted whey applied to a large area would have any bad effects on plants. The protein in the whey will decompose and eventually become plant food. I would not apply it to a concentrated spot, because I think raccoons, possums or dogs might dig up the area.
Q: How late can zoysia sod be planted this summer and still have time to take root before cold weather? — Cathy Rainer, email
A: I think you'd be safe planting it 90 days before the first frost. There still would be plenty of good quality sunshine then to get the grass rooting quickly. Sometime between now and early August probably would be fine to lay the sod, as long as you can water it appropriately.
Q: We recently had stones placed on the bank of our detention pond to prevent erosion. Many animals and birds live there. Weeds are growing between the stones. We need an environmentally safe herbicide to kill the unwanted plants. — David Bauman, email
A: I am comfortable recommending a glyphosate product that is labeled for aquatic use (Rodeo, etc.) and which is then mixed with a nonionic crop oil surfactant (Cygnet, Cide-Kick, etc.) to help it stick to plant leaves. Weed killers that are considered organic and labeled for landscape use have not been tested for safety in pond environments, so I do not recommend them. I have details on pond weed control at bit.ly/GApondweed.
Q: Do you think we can grow New Zealand tree ferns in Atlanta? — Susan McCabe, email
A: They won't survive winter. I see them for sale at "big box" stores as perennial plants, but I just roll my eyes and pass them by.
