MURPHYSBORO, Ill.— By the end of the summer season, most gardeners are ready to put up their feet and enjoy a bonfire, but it’s a great opportunity to take stock of what worked in the garden the past year, what needs changing, and what can be added. Springtime is crunch time with so many gardening projects going on. Planting in the fall is like putting money in the bank for next year. This is an investment in improved performance of plants in the spring and more time for other projects.

Perennials like trees, spring/summer flowering shrubs, and spring blooming ephemerals should be planted about six weeks before the first frost of the year. Here in southern Illinois, the first frost date is historically in the last two weeks of October. Further up-state it could be a week or two sooner than that, so be sure not to plant too close to the first frost. In the fall, soils hold onto heat longer while the above ground temps may be dropping. This is ideal for new root structures to grow. The root systems need time to establish new micro or feeder roots in the soil which helps the transplant to acclimate, then gradually go into dormancy as colder winter temperatures arrive. An improved root structure is the main advantage over spring transplants because they typically have more time to acclimate to the local environment.

Ensure that plants are well anchored and planted in the soil to avoid frost heaving during winter. The collar of the plant should be level with the soil. If it’s sitting above the soil line, water can wick away quickly and kill the roots. If it’s too deep, the roots can be smothered from lack oxygen. Thoroughly water plants when they are installed and water as needed up to the first hard frost. Even if it warms up a bit in late fall or early winter, its best to hold off on watering to avoid interrupting the hardening off process. The same applies to fertilizer application in fall and is not recommended. The addition of nitrogen and other nutrients in the fall can cause the transplant to put energy into new vegetative growth that will be damaged by winter conditions and suppress the establishment of roots. It’s best to hold off on fertilizing until early spring. However, it is a great idea to add a 2” to 3” layer of mulch around the base of plants, making sure to leave some open space around the trunks and stems to avoid harboring unwanted pests and moisture build up. Fall plants don’t need to be mulched right away and can benefit from the sun warming the soil. Mulching can wait until night-time temps are getting around 32°F. By adding mulch like straw or wood and making sure plants are well anchored in the soil, frost heaving can be avoided. Adding fall compost around new plants is also a great idea. By spring, most of the compost will be broken down and ready to be taken up by plants with root structures that have a head start on spring transplants.

Benefits of planting perennials in the fall:

  • Improved root structure and resistance to fluctuating spring weather.
  • Faster and more abundant bloom time in spring and summer.
  • Improved vigor and resistance to stress.
  • Improved suppression of warm-season weeds.

A few key tips to keep in mind for successful fall planting are:

  • Order and buy plants with enough time to plant six weeks ahead of the first frost.
  • Make sure to water them in well, then water as needed and stop watering after the first hard freeze.
  • Help overwinter fall transplants with mulch and compost.
  • Do not feed new transplants until spring, but adding compost in thefall is okay.

As Horticulture Educator, Little oversees horticulture programming within Franklin, Jackson, Perry, Randolph and Williamson counties. He is instrumental in working with the Master Gardener and Master Naturalist volunteer programs. He is available to assist the community and answer questions on a variety of horticulture related topics including home gardening, residential and commercial horticulture, small-scale fruit and vegetable production, urban agriculture, soil fertility, integrated pest management as well as landscaping. For more information on seed collecting, contact Little at (618) 687-1727.

University of Illinois Extension provides equal opportunities in programs and employment. If you need a reasonable accommodation to participate in any of our programs, please contact your local county extension office. Early requests are strongly encouraged to allow sufficient time for meeting access needs.

News Source: Austin Little (618) 687-1727, little84@illinois.edu

News Writer: Heather Willis (618) 357-2126, hdwillis@illinois.edu