Q. Where can I find those beautiful Persian buttercups like the ones at the Flower & Garden Show this year?
–Heidi Thorsen, Oak Park
A. Ranunculus asiaticus or Persian buttercup is a tender (not hardy) flowering tuber that produces spectacularly bright, round, heavily petaled flowers. In the Chicago area, it is commonly grown as a cool-season annual and can be set outside in the garden or containers in mid-April, once it has been completely hardened off.
You can purchase fully growing plants in better garden centers next month, or buy tubers through mail order or good garden centers, and start your own plants indoors.
Be sure to obtain growing instructions when you order tubers, since they must be soaked for 24 hours before planting them in light soil in full sun.
Q. I planted some shrub roses early last spring and was told to wait one year before fertilizing them. What product do you recommend and when is the best time to apply it?
–Julia Leimsieder, Antioch
A. For roses to produce an ongoing show of flowers, they must have a regular supply of supplemental nutrition. It’s not necessary to wait one year before beginning this program. In early spring, when the forsythia is in bloom, prune away all dead wood and fertilize your roses with a high-nitrogen, slow-release, organic granulated fertilizer.
Most soils in the Chicago area are high in potassium and phosphorus, so these elements are not required at this time.
You can fertilize your plants three more times with a liquid 20-20-20 mix: first, after the shrub has completely greened up; next, after the first flush of flowers has appeared; and the third and final time would be in mid-July. Avoid fertilizing roses after Aug. 1.
Q. I have some unusual ferns in my garden and wonder if I can propagate them from the spores on the underside of their leaves.
–Jackson Heinz, Evanston
A. The most common method to propagate a perennial fern is to divide the plant’s rhizome in late summer or early fall. Propagating from spores can be extremely time-consuming and risky for the average gardener. All materials involved in fern propagation must be sterile. This includes pots, the planting mix, tools and even the water used for misting.
If you welcome a challenge, cut a large healthy frond in autumn, full of spores, and place it between two large sheets of paper towels, spore side down. Cover the towels with a weight. In two days spore dust will be evident on the towel. Transfer the dust to a small planting dish containing an inch or two of sterile soilless mix. Carefully sift peat moss over the spores; mist and cover the dish. Place it in a window out of direct sunlight. In several weeks fuzzy little ferns will appear on the surface. Divide these once more into sterile larger pots filled with potting soil, not soilless mix. When there is no danger of frost (around mid-May), gradually move the small ferns to the outdoor garden.
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Lee Randhava writes for the Chicago Botanic Garden in Glencoe. She cannot reply individually but will select questions of general interest to answer in this column. Send your concerns to: Gardening Q&A, Home&Garden, Chicago Tribune, 435 N. Michigan Ave., Chicago, IL 60611-4041, or send e-mail to home&garden@tribune.com.