Q: I have an island of winter jasmine that blooms every year from December through February. I wonder why it flowers in the dead of winter if the primary purpose of showy flowers is to attract insects for pollination. Dan Cowles, Cumming
A: Winter jasmine, Jasminum nudiflorum, was introduced from China in 1844. Its slender green stems and bright yellow flowers remind gardeners of forsythia. It makes an excellent cascading vine for a hillside. It never seems to overpower its neighbors. One theory holds that the flowers would be pollinated during the warmer winters of the Chinese region where it originated. Here, though, pollinating insects are absent during winter. Another theory is that most, if not all, winter jasmine plants in the U.S. are descendants of a single plant that came over in 1844 and are self-incompatible: They need pollen from a different member of the species left behind in China. You can propagate winter jasmine by burying stems and allowing them to root during summer.
Q: I have 30-year-old red tip photinias that are 25 feet tall. I'd like to "down size" them. Am I correct that this should be done only in early spring prior to new growth? And is it permissible to take them down more than one-third in height a year? I'd like to get them to about eight feet. Geoff Coulborn, email
A: My usual advice on pruning photinia is to do it in summer, which results in fewer disease-prone young leaves. But if you want to severely reduce the size of a big photinia, the best time to do it is in early spring, perhaps late February. This will give plenty of new growth but it will come with the necessity of spraying it with fungicide to prevent leaf spot disease. Apply fungicide from budbreak until June. In succeeding years, prune in the dry part of summer to keep the shrubs in bounds and leaf spot free.
Q: I'm looking for definitive books for identifying shrubs and vines, We have many identification books but none of them seem to have everything: color pictures, index by color, leaf shape, etc. I already have the shrub book by George Symonds and the Petersen Field Guide. LuAnn Jinks, email
A: Native-plant expert Shannon Pable (www.shannonpable.com) recommends "Newcomb's Wildflower Guide" by Lawrence Newcomb, "Wildflowers of the Eastern United States" by Wilber and Marion Duncan plus "Appalachian Wildflowers" by Thomas Hemmerley. Shannon says if you want to get down to the nitty gritty of classification, try "Botany in a Day" by Thomas Elpel. It teaches about plant families, which will significantly help you zero in on identifying plants.
Q: For the past three summers I have had a problem with whiteflies in my garden. I first notice them on the underside of leaves on my tomatoes. Before the summer is over, they have attacked any other plant that is still green. What do you recommend? Clay Dotson, Young Harris
A: If you hit them early, whiteflies can be controlled with organic insecticides like neem oil or spinosad (Captain jack's Dead Bug Brew). You can also use synthetic contact insecticides like permethrin (Eight Vegetable, Fruit and Flower) or cyfluthrin (Bayer Vegetable and Garden). If you want systemic action, imidacloprid (Bayer Fruit, Citrus and Vegetable Insect Control) will do a fine job on whiteflies.
