Fall is a great time for getting perennials into the ground. This time of year the soil is still warm, which is better for root establishment before spring growth and summer heat. Even established perennials can benefit from some fall maintenance.
Identify blank spaces in the landscape that could benefit from additional plants. Understand the growing conditions of these areas including soil, light, water and even the size of the space available. Select perennials you like based on their suitability for the space.
Blooms are a key determinant for many gardeners when selecting plants. This commonly includes color but should include shape as well. Erect plumes of astilbe (Astilbe sp.) create an interesting contrast to the rounded globes of allium (Allium sp.). Choose colors that complement each other considering foliage color as well. Perennials with grey or silver foliage such as artemisia (Artemisia sp.), woolly thyme (Thymus pseudolanuginosus) and snow-in-summer (Cerastium tomentosum) are lovely displayed among perennials with leaves in shades of green.
Bloom time should also be considered to keep the garden flowering for as much of the growing season as possible. While preferable for the gardener and other spectators for obvious reasons, a longer bloom season benefits pollinators as well. False indigo (Baptisia australis), spurge (Euphorbia sp.) and creeping phlox (Phlox sp.) are all spring bloomers. Red hot poker (Kniphofia), baby’s breath (Gypsophila) and coneflower (Echinacea sp.) bloom during the summer. A few late summer/early fall-bloomers include: Aster (Aster sp.), anemone (Anemone sp.) and joe-pye weed (Eutrochium).
Also consider the intention for the landscape. Perennials for rain gardens, xeriscapes, erosion control, privacy and many other purposes can be selected to benefit the environment and gardeners alike. Plants that are specifically suited for these conditions should be included for the best chance of establishment and the least amount of maintenance.
Once plant selection and placement are complete it’s time to get your hands dirty. Dig each hole to the same depth as the plant was in its container. The hole should be twice as wide as it is deep. Remove the plant from the container and loosen the root ball to spread out the roots. Roots that are tightly wound inside the container will continue to grow in this way if not spread and redirected. This can result in girdling and restricted growth. Place the plant in the hole and backfill using the original soil mixed with compost. Tamp the soil as you backfill to remove air pockets.
Mulch the surface around perennials 1 to 2-inches deep. This helps to prevent weed growth and retains moisture. Mulch can also regulate the temperature preventing freeze damage. However, too much mulch can increase the risk of rot at the plants’ crown. It is best to remove weeds that do appear by hand-pulling. Young perennial roots can be easily damaged by cultivation if not careful.
Perennials, whether newly planted or established should receive at least 1 inch of water each week to promote root development. Deep waterings encourage deeper root growth. During heat waves more water may be necessary.
If you’re struggling with choosing perennials for your yard, take time to stroll through the neighborhood and enjoy other gardeners’ hard work. Visit botanical gardens and parks making note of plants that work well together and create an arrangement you find visually pleasing. Local extension agents are also a great resource for advice on plants that work well in specific landscape situations.
Cynthia Domenghini, PhD, is an instructor of horticulture and garden management for Kansas State University’s Horticulture and Natural Resources Department.