Q. I purchased a spider mum plant from a well-known florist. If I plant it outside, is there any chance it will make it through winter?
--Jackie McKay, Evanston
A. No, most seasonal flowering plants offered in floral shops have spent their lives in greenhouses and cannot make the brief transition from a protected environment to a Chicago winter. Chrysanthemums purchased at this time of year should be considered annuals meant to provide seasonal color in containers and window boxes, or to be enjoyed indoors as a short-lived houseplant.
True perennial chrysanthemums can be purchased as small 4-inch plants from reputable nurseries in spring and set out in the garden. They then benefit from an entire growing season acclimating to your garden and developing a strong root system. These newly planted mums should be mulched in late fall once the ground has frozen.
Q. I have a beautiful terra cotta fall container with mums, kale, purple verbena and an annual burgundy fountain grass. Is there any way I can save the grass for next year?
--Meredith Turner, Winnetka
A. It's very tricky trying to overwinter plants in outside containers. You'll have a better chance for success if you can bring the container into a dark, cool basement or garage where temperatures remain fairly constant in the low 40s. This month, gradually decrease the plants' water.
After we have had a few frosts, the grass will go dormant and change from burgundy to tan. Remove the other plants from the container, cut the grass back to one-third of its original size and move it into the garage. Check the soil over winter and water it just enough to keep it from getting bone dry. You don't want to break its dormancy.
As spring approaches, gradually move the container to a spot where it will get more light and resume normal watering. Gradually acclimate the plant to outdoor conditions for one week. Annual grasses can be seriously damaged by an unexpected late-season frost.
Q. I planted dahlias for the first time this spring. The flowers were beautiful but the plants sprawled all over. How do you deal with these tall plants?
--Todd Sperling, Chicago Heights
A. This is common when tall dahlias are grown without support. Plant these tubers at least 7 inches deep. At that time, insert several tall, sturdy stakes in a wide circle around the tuber. Staking later in the season runs the risk of puncturing the growing tuber.
As the plant grows, guide the stems early to the stakes and tie them gently with soft cloth or strips of nylon stockings (not wire or twist-ties). Pinch the growing tips to stimulate bushy rather than gangly growth. Some growers prune out side growth, creating fewer but larger flowers.
Since mature branches are hollow and brittle, any attempt to lift and tie them can result in broken branches. Dahlias are heavy feeders, but avoid high-nitrogen mixes. Site your plants in full sun but provide protection from wind.
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 firstname.lastname@example.org.