Perennial plants live for more than two years, returning each season from the same root structure. They do not need to be replanted annually like seasonal flowers or vegetables. While perennials are permanent fixtures, they often require periodic maintenance called division to remain healthy and vigorous. Division involves physically separating the plant clump and replanting the resulting sections.
Why Perennials Remain in Place
Perennials possess a specialized biological system that allows them to survive adverse weather conditions, such as winter freezing or summer drought. They invest heavily in developing extensive root systems and storage structures like crowns, rhizomes, or tubers. These underground parts store carbohydrates and nutrients to fuel the next season’s growth.
When temperatures drop and daylight hours shorten, the plant enters dormancy, and the above-ground foliage often dies back. The established root system remains alive below the soil line, allowing the plant to regenerate reliably each spring. Replanting is therefore not an annual necessity but a corrective gardening practice.
Signs That Division is Required
Although perennials are long-lived, the initial planting site eventually becomes overcrowded, signaling the need for division. This overcrowding causes the dense root system to compete aggressively for limited water and nutrients. A visual indicator that a perennial is struggling is the development of a bare or dead center, often described as a “doughnut” appearance. As clump-forming plants mature, the oldest growth in the middle becomes unproductive and dies out.
Other signs include a noticeable reduction in the number or size of flowers, stems that become floppy and require staking, or a general look of reduced plant vigor. Division helps break up this congestion, increase air circulation, and encourage fresh growth from the healthier outer sections.
When to Divide Perennials
The optimal time for dividing perennials minimizes transplant shock and maximizes recovery. The general rule is to divide a plant when it is not actively flowering, allowing it to focus energy on establishing new roots. This usually places the task in the cooler periods of early spring or early fall.
Spring Bloomers
For spring-blooming perennials, such as irises or daylilies, the best time for division is late summer or early fall. This should be done four to six weeks before the first hard frost. This timing allows the newly separated sections to develop a root system before winter dormancy.
Fall Bloomers
Conversely, fall-blooming perennials like asters should be divided in the early spring, just as new growth begins to emerge. Dividing them in the spring prevents the disruption of their current season’s bloom cycle and gives them the entire growing season to settle in.
Executing the Division and Replanting Process
Successful division begins with preparation, which includes thoroughly watering the plant the day before. This reduces stress and makes the soil easier to work with.
Lifting the Plant
To lift the plant, use a garden fork or spade to dig around the entire clump, starting at the drip line. This ensures the majority of the root mass is retained. Once the root ball is loosened, gently lever the entire plant out of the ground.
Separating the Root Mass
Separate the root mass into smaller, healthy sections, each containing several vigorous shoots or “eyes.” Loosely matted roots can often be pulled apart by hand. For dense, woody root systems, use a sharp knife, spade, or two garden forks to pry the segments apart. Discard the old, woody, or dead center of the original plant, as this is the unproductive part.
Replanting Divisions
The healthy divisions should be replanted immediately into freshly amended soil at the same depth they were growing previously. The planting hole must be wide enough to allow the roots to spread naturally. After replanting, water the new divisions deeply and thoroughly to settle the soil around the roots and eliminate air pockets. Applying a layer of mulch helps to retain soil moisture. For the first week, new transplants should be protected from intense, direct sun to facilitate recovery.