Q. What is the secret to growing snapdragons that bloom all summer long? I planted the very tall, double-flowered varieties this spring and they have just pooped out on me.
--Rhoda Petersen, Chicago
A. To get the maximum number of blooms from your snapdragons, Antirrhinum majus, pinch back the small plants when you first plant them in spring. This promotes lateral branches and discourages leggy, floppy growth common to the taller varieties. Staking the tall plants early in the season also is recommended. Make sure they are planted in full sun in rich soil with adequate moisture.
Once they flower, cut back flower stalks and fertilize the plants with a 15-15-15 mix. This should promote another flush of flowers. Snapdragons may flag in hot, humid weather but often can be persuaded to bloom again as less humid weather returns.
Q. What are the current "dog-friendly" controls for dealing with slugs. My hostas, ligularia and sweet potato vine are riddled with holes.
--Katherine Heinz, Evanston
A. Slugs are a common problem in moist, shaded gardens and they are particularly fond of tender new seedlings, fallen fruit and soft, large-foliaged plants that grow close to the ground. Hostas with blue, thick, corrugated leaves often are more resistant to slugs than the thin-leaved varieties.
One non-chemical suggestion is to cut old screens into 1-inch strips. "Frame" your prized plants by sinking the strips half way into the soil, with a ragged 1/2 inch above soil level, making sure there are no slugs inside the frame. You also can roll up a few sheets of damp newspaper and leave the roll close to the hosta. Slugs feed at night and hide under the paper during the day. Dispose of the paper (and slugs) in the morning.
Another option is to sink tuna cans into the soil and half-fill with a mixture of beer and a little flour. The slugs are attracted to this yeasty mix and will climb in and drown.
Since slugs overwinter as eggs hidden under garden debris, be sure to clean up your garden beds of all dead plant material in late fall to reduce future generations of slugs.
Q. I have a variegated `Autumn Frost' sedum that occasionally produces non-variegated leaves. What should I do?
--Barbara Kincaid, Glenview
A. It is not unusual for perennials, grasses or even shrubs with variegated foliage to revert to solid color leaves from time to time. Immediately prune out all stems bearing non-variegated foliage to discourage this tendency.
Lee Randhava writes for the Chicago Botanic Garden in Glencoe.