Summer Care for Fall-blooming Perennials

As the summer gardens start to lose their glamour, many gardeners look toward mums and asters to add fall color to our gardens and planters. However, many of us find that our mums and asters are not performing as well as they should, or are growing tall and leggy rather than the compact, bushy plants that we would desire. Mums and asters are one of the showiest and most reliable perennials in the fall garden, however, for optimum performance, some simple steps need to be followed in early spring to mid-summer. Mums should be divided once a year in early spring. Dig up the entire plant and separate growing shoots and discard older, woody, central parts of the plant. To get compact, bushy plants with lots of flower buds, pinch the growing tips as soon as the plants are 6 to 8 inches high. This stimulates branching and the onset of more flower buds. Within weeks after pinching, new shoots will form. When these new shoots are 6 to 8 inches long, pinch back again. In Missouri, pinch three to six times until mid-July. After the second or third week in July, discontinue pinching and allow the plant to fully develop flower buds. Mums also need regular watering because their roots tend to be shallow. Drought will cause woody, stunted growth. Mums are also heavy feeders and require regular fertilizing until mid-August. To increase mum’s survival rate in the winter, avoid pruning them back after frost hits. A horticulture professor at Iowa State University tested 19 varieties and found that plants left unpruned survived the winter better than those that were cut back in the fall.

Another flower prized for their brilliant late-autumn bloom and long bloom period are perennial asters. Asters are a wonderful way to usher in the autumn season with magnificent flowers well past the first frost. Aster flowers also provide nectar for migrating monarch butterflies each fall. There are many different varieties of asters. One of the showiest is the native aster, New England aster (Aster novae-angliae), which grows throughout much of Missouri. Among some of the more popular varieties for a compact, bushy growth habit are Patricia Ballard, Professor Kippenberg, and Alma Potschke. For optimum performance, asters should be dug up and divided every two to three years. As with mums, select for replanting the vigorous outer shoots and discard the woody central growth. Asters tend to grow tall and somewhat leggy, however, cutting stems back halfway in early summer will make the plant shorter, stronger, and bushier. Asters prefer well-drained soil and a sunny location and tend to be quite drought tolerant.

Mary Kroening
Horticulture
573-882-9633