Plant division, often called splitting, is a common horticultural technique used to propagate new plants and rejuvenate mature, clump-forming perennials. This practice relies on the plant’s natural tendency to expand outward from a central crown, creating a dense mass of roots and stems. By physically separating these clumps, gardeners can prevent overcrowding, which often leads to reduced air circulation and increased competition for soil nutrients. The process stimulates vigorous new growth, often resulting in improved flowering performance in the subsequent growing seasons.
Choosing the Right Time and Plant
Division is typically performed on perennials that grow in dense clumps, such as hostas, daylilies, ornamental grasses, and irises. These plants benefit from being separated every three to five years to maintain health and flowering capacity. An established plant often signals its need for division when its flowering diminishes, or when the center of the clump becomes visibly dead or woody.
The timing of the division process is governed by the plant’s physiological state, aiming to minimize stress during periods of active growth. Most perennials should be divided during their natural dormancy period, which occurs in late fall after the foliage dies back or in early spring just as new growth emerges. Dividing during dormancy allows the plant to focus energy reserves on establishing new roots rather than supporting a large canopy of leaves. Plants that bloom in the summer or fall are best divided in the spring, while spring-blooming varieties are split in the late summer or fall.
The Physical Division Process
Before beginning the process, gather the necessary tools, including a sharp spade or garden fork, a sturdy trowel, and a clean, sharp cutting implement like a knife or pruners. Sterilizing the cutting tools with rubbing alcohol or a bleach solution prevents the transmission of pathogens between plants. The initial step involves carefully excavating the entire clump, digging wide around the plant’s drip line to ensure minimal damage to the feeder roots.
Once the root ball is lifted from the soil, gently remove excess dirt by shaking or using a gentle stream of water to expose the root structure and crown. The method of division depends on the plant’s root structure. Plants with fibrous, tangled roots, such as hostas or dense ornamental grasses, are often best separated using two garden forks inserted back-to-back into the clump and leveraged apart. Perennials with thick crowns, like irises or peonies, require a sharp knife or spade to cut through the dense material.
Each resulting section must be a viable plantlet, possessing a sufficient mass of healthy roots and at least one or two growth buds, sometimes called “eyes.” These buds represent the points from which new foliage and flowering stems will emerge. As you separate the clump, any old, woody, or dead material from the center of the original plant should be discarded, as this material is spent and less vigorous. Trimming back the foliage by about one-half to two-thirds before replanting helps reduce moisture loss through transpiration, easing the burden on the newly disturbed root system.
Essential Care for Newly Split Plants
After the sections are separated, immediate replanting is necessary to prevent sensitive root tissues from drying out, a condition known as desiccation. The new planting hole should be prepared with loose soil and beneficial organic amendments, such as compost, which will improve drainage and nutrient availability. Each new section must be placed in the soil at the same depth it was growing previously, ensuring the crown is not buried beneath the soil line.
The most important step immediately following replanting is a deep, thorough watering. This initial drenching eliminates air pockets that may have formed around the roots during the replanting process. Eliminating these air pockets is a primary mechanism for reducing transplant shock, allowing the roots to establish immediate contact with the surrounding soil particles. For the first few weeks, the new divisions require consistently moist soil and may benefit from temporary protection from intense, direct afternoon sunlight.