Plant division is a straightforward method used to propagate new plants from existing, established specimens. This process involves physically separating a mature plant into smaller sections, each capable of growing into a standalone individual. Gardeners use this technique for two primary reasons: to efficiently increase their plant stock and to maintain the health and vigor of crowded plants. Over time, many perennials develop a dense root mass that can lead to reduced flowering and general decline. Division effectively remedies this condition by breaking up the congested crown, allowing the plant renewed access to soil nutrients and moisture.
Identifying Suitable Candidates for Division
The suitability of a plant for division is determined by its root structure and growth habit. Plants that form distinct, expanding clumps are generally the easiest and most successful candidates for this vegetative propagation. These specimens create multiple growing points or crowns that can be cleanly separated from the parent plant.
Clumping perennials are the most common type for division, characterized by a central crown that expands outward over time. Examples include Hosta, known for its fibrous root system, and Daylilies (Hemerocallis), which develop thick, fleshy roots. When these plants become overcrowded, their centers often die out, signaling that division is needed to rejuvenate the clump.
Another major group consists of plants that grow from specialized underground stems, such as rhizomes or tubers. Bearded Irises, for instance, spread via thick, horizontal rhizomes that lie just below the soil surface, producing new growth fans. These younger sections are easily sliced away and replanted. Similarly, some spring-flowering bulbs, like Daffodils, naturally produce offsets, which are small “daughter” bulbs that cluster around the parent. Removing and replanting these offsets provides an effective method of propagation.
Optimal Timing for Successful Division
The success of plant division relies heavily on timing; it is best performed when the plant is not actively growing or flowering. Dividing a plant during its peak growth or bloom cycle diverts energy needed for recovery, causing stress and potentially leading to death. The goal is to move the plant during dormancy or just as active growth is beginning.
A general rule is to divide plants based on their flowering period. Spring-blooming perennials, such as Peonies, are best divided in the fall, allowing roots time to establish before the ground freezes. Conversely, plants that flower in the late summer or fall, like Asters and Garden Phlox, should be divided in the early spring as soon as new growth emerges. This timing gives them a full season to recover and develop a robust root system.
Gardeners should conduct division on a cool, overcast day to minimize transplant shock and prevent exposed roots from drying out. Avoiding the hottest part of summer is important, as high temperatures coupled with root disturbance place excessive demands on the plant’s resources. Dividing at the correct time ensures the plant’s energy is focused on root regeneration rather than supporting foliage or flower development.
Step-by-Step Division Technique
The process begins by preparing the plant a day or two in advance, ensuring it receives a thorough watering to hydrate the tissues and loosen the soil. Before lifting, the foliage should be cut back by about one-half to two-thirds; this reduction minimizes moisture loss and reduces the energy required to support the leaves. The entire clump is then carefully lifted from the soil using a garden fork, working outside the perimeter of the crown to preserve the root system.
Once the root ball is out of the ground, excess soil should be gently shaken or rinsed off to expose the roots and the individual growing points, or “eyes.” For plants with loose, fibrous roots, such as ornamental grasses, the clump can often be separated by pulling it apart by hand. For dense, woody crowns like those found on mature Hostas or Daylilies, a sharp, clean tool is necessary.
A sharp knife, spade, or two back-to-back garden forks inserted into the center of the crown can be used to cleave the root mass into smaller sections. The size of each division is important; a viable new plant must retain a healthy root mass and at least one, but ideally three to five, vigorous growth buds or shoots. The older, weaker, or dead material from the center of the original clump should be discarded.
Essential Care After Dividing
Once the divisions have been separated, they must be replanted immediately to prevent the exposed roots from drying out, which can lead to plant death. If immediate replanting is not possible, the new divisions should be temporarily protected by covering the roots with moist burlap or placing them in water. Proper soil preparation involves incorporating organic matter to improve drainage and nutrient retention.
The divisions should be planted at the same soil depth as the original plant, ensuring the crown remains level with the surrounding soil surface. After planting, the new divisions require deep and immediate watering to settle the soil around the roots and eliminate air pockets. Consistent moisture is required during the establishment phase, typically the first four to six weeks, as the damaged root systems regenerate.
Monitoring the newly planted divisions for signs of transplant shock, such as wilting or drooping leaves, is important. Applying a starter fertilizer, which is low in nitrogen and high in phosphorus, encourages new root growth and helps the plant establish itself. Providing temporary shade for a few days, especially during hot weather, can also reduce stress and increase the likelihood of successful recovery.