Mumma Mia! Mums provide a splash of color to your fall garden

I am interested in adding some late-season color to my garden and would like some tips on how to grow the mums I have been seeing in garden centers. Is it too late to plant them this fall?

— Charlie Marsden, Lake Forest

Garden mums (Dendranthema X grandiflora) are readily available in a wide range of colors for purchase and are a great way to add late-season color to your garden. You may also see the terms hardy mums, fall mums and chrysanthemums used for these plants at garden centers. Garden mums are short-day plants and initiate flower buds in response to an interaction of day length, temperature, and plant age. Different mum varieties will come into flower at different times in fall based primarily on their responses to day length. Early-season varieties can be expected to come into flower in early to mid-September, mid-season varieties from mid to late-September, late-season varieties from late September to early October and season extenders from early to mid-October. Most mums are purchased in late August through September, but you should still be able to find them. Asters are another good option for adding color in the late season and will blend nicely into perennial borders.

The best stage to purchase a garden mum is when the buds are just showing some color. Mums that are on special with fully open flowers are OK to buy, but be aware that they will not last as long in your garden. Depending on weather conditions and mum varieties, you can expect to get a good display of color for four to six weeks. Extended periods of hot weather will age the flowers more quickly. I prefer to buy mums when the buds are just starting to show color — this will ensure the longest display time in your garden. If you plan to plant the mums in a shaded garden site, then it will be best to purchase mums with flowers that are more open as mums that are in tight bud may not open properly if planted into a shady garden site.

Be careful when transporting and planting your mums as the buds are very easy to break. The mums should not be allowed to dry out after planting as this can reduce the flowering time, so pay close attention during warm and sunny fall weather when you may need to water the plants every two to three days. Check the root balls with your finger to assess whether the plants are dry, as there will not be much root development out into the garden soil throughout their time in the garden. There is no need to fertilize the mums.

Most gardeners plant mums too late in the fall for the plants to survive through winter. Some of the mums may come back next year if they are mulched. The shallow-rooted mums that are planted late in fall while in full bud or flower do not have enough time to establish before winter sets in. The best way to incorporate hardy mums into your permanent border will be to purchase and plant them in spring, though the color selections will be very limited at that time of year.

For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.