Overwinter Your Flowering Annuals
by Don Janssen, Extension Educator
Fall means that killing frost will soon put an end to the flowering annuals you have enjoyed all summer - unless you save some of them to grow indoors this winter. The most commonly overwintered annuals are geraniums, coleus, impatiens and fibrous-rooted begonias, and the key to enjoying indoor flowers is light.
Too little light will result in long, straggly stems and few, if any , flowers. Leaves will be few, also, and widely spaced on the stems. Because winters are not exactly famous for lots of bright, sunny days, growing theses plants indoors usually means growing them under fluorescent tubes.
There are two ways to approach saving annuals to grow indoors: starting new plants from cuttings and digging up and potting whole plants. Whole plants will need larger containers and more potting soil, but they may bloom sooner.
To save whole plants, select healthy, growing plants, cut the tops back by half, and then dig them up with as much of the root systems as you can and pot each plant in a container big enough to hold all the roots comfortably. Remove as much garden soil from the roots as you can without seriously damaging the roots, and use a commercially prepared houseplant potting mix in the pots. Garden soil will not drain as well and may contain weed seeds, insects, disease organisms and other pests. Keep these plants separate from other indoor plants for at least a few weeks in case pest problems develop.
Cutting the plants tops back makes them easier to handle and brings the top growth into better balance with the reduced root system.
To grow new plants from cuttings, begin with 3- to 4-inch tip cuttings from the tops of plants. Cut with a sharp knife to avoid mashing or tearing the stems. Remove the leaves on the bottom third or half of each stem. Then insert the cut end into damp perlite, vermiculite, or sand. You can use a rooting hormone, but it may not be necessary.
Place the container with the cuttings out of direct sunlight and water as needed to keep the rooting medium moist. It should take about six weeks for them to develop roots 1/2 to 1 inch long. Then you can transplant them into 4-inch pots of houseplant potting mix and move them to a brightly lighted spot - either a sunny window, where they'll need frequent turning to keep them from growing lopsided, or under artificial light.
Both whole plants and those grown from cuttings will benefit from pinching. Removing the growing tips regularly will encourage plants to branch rather than straggle.
Plants are more likely to grow compact and bushy and flower indoors if you grow them under fluorescent tubes rather than natural light. A mixture of cool-white and warm-white bulbs is recommended, but all cool-white bulbs will be satisfactory. Place the bulbs no more than 12 inches above the plants. To simplify the lighting, put the lights on a timer set so they receive 12 to 16 hours of light a day. In the spring, wait until the danger of frost is past and then cut plants back to about one-third of their height and transplant outdoors.
University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office