Perennials live for more than two growing seasons; herbaceous varieties typically die back each autumn and regrow in the spring. The above-ground foliage enters a dormant state as temperatures drop, but the root system remains alive to fuel the next season’s growth. Fall care focuses on preparing the root crown for successful winter dormancy and maximizing energy reserves for a vigorous bloom cycle in the coming spring. This transition period allows gardeners to perform maintenance that impacts the plant’s long-term health and survival.
Managing Spent Foliage
Deciding whether to cut back spent foliage depends on the specific plant, its health, and the gardener’s preference for winter appearance. For many perennials, wait until after the first hard frost causes the foliage to completely yellow or brown. This waiting period allows the plant to reclaim valuable nutrients and carbohydrates, sending them down to the root structure for winter storage.
The primary reason to cut back foliage in the fall is to prevent the overwintering of pests and diseases. Plants that suffered from issues like powdery mildew (Phlox, Bee Balm) or leaf spot should be pruned close to the ground. All infected material must be removed from the garden and not added to the compost heap. Hostas should also have their leaves removed after frost to eliminate slug eggs.
Conversely, many perennials benefit from leaving their spent foliage standing until spring. Ornamental grasses and plants with rigid, attractive seed heads, such as Sedum ‘Autumn Joy’ and Coneflower (Echinacea), provide visual interest against a snowy landscape. Leaving the seed heads also offers a food source for birds throughout the colder months. Furthermore, the standing debris provides a natural layer of insulation, helping to protect the plant’s crown from temperature fluctuations and severe cold.
Dividing and Moving Established Clumps
Division is a rejuvenation technique necessary for mature perennials that show signs of overcrowding, such as decreased flower production or a ‘dead’ center where the oldest growth has died out. This process increases air circulation within the clump and stimulates new, vigorous growth. The cooler temperatures of fall are less stressful on the exposed roots of a newly divided plant, reducing transplant shock.
Fall is the preferred time for dividing spring- and summer-blooming perennials, allowing four to six weeks for root establishment before the ground freezes. To begin, lift the entire clump from the soil using a spade, digging four to six inches away from the plant’s base. The root ball is then split into smaller sections by gently teasing the roots apart, cutting with a sharp tool, or using two garden forks placed back-to-back to pry tough clumps apart.
Each resulting division should retain three to five healthy shoots and a robust portion of the root system. Discard the woody, depleted center of the original clump, and immediately replant the new divisions at the same depth as the parent plant. Adequate soil amendment in the new location and a thorough watering following transplanting are crucial steps to minimize desiccation and encourage rapid root growth.
Preparing the Soil for Dormancy
Proper soil management ensures the perennial’s roots are well-hydrated and insulated for the winter. Before the temperature drops consistently below freezing, a final, deep watering of the garden bed is essential. This “freeze-up watering” saturates the soil to a depth of four to six inches, ensuring the root system is fully hydrated to resist desiccation throughout the winter.
Once the ground has frozen hard, apply a layer of protective mulch around the perennial crowns. Applying mulch too early can trap moisture and heat, potentially delaying dormancy or encouraging fungal growth. The mulch, which can be straw, shredded leaves, or wood chips, acts as an insulating blanket to keep soil temperatures consistent. This consistency prevents the freeze-thaw cycles that cause soil heaving, where the expansion and contraction of the soil push the root crown out of the ground.
Before applying mulch, clear the garden beds of weeds and any remaining plant debris that could harbor pests or pathogens. A clean environment reduces the likelihood of slugs, snails, or diseases surviving the winter. Spread a two to four-inch layer of loose organic mulch around the plants. Take care to keep the material a few inches away from the perennial’s crown to prevent moisture buildup and rot.