Crocosmia, commonly known as Montbretia, is a vigorous, cormous perennial prized for its late-summer display of fiery, arching flower spikes. These plants naturally multiply and form dense clumps over time. Division is a necessary maintenance task to ensure the plant continues to produce healthy foliage and prolific blooms. This process rejuvenates the plant’s vigor by reducing intense competition for nutrients, light, and space within the crowded clump.
Recognizing the Need for Division
The need for division becomes apparent through several physical indicators in the plant’s appearance and performance. Crocosmia forms chains of corms that stack vertically and multiply horizontally, leading to severe congestion after a few seasons. This overcrowding starves individual plants, resulting in a noticeable reduction in flowering. The most common signals are a decrease in flower production (fewer or smaller flower spikes) and reduced plant vigor, often seen as a dying or declining center of the clump. For most varieties, division should be performed approximately every three to five years to prevent congestion and maintain plant health.
Optimal Timing for Division
The best time to divide Crocosmia is when the plant is dormant, minimizing transplant shock. There are two primary windows for this task: early spring and late fall. Early spring is often preferred, just as new growth begins to emerge but before it fully develops. Dividing in spring allows the corms to establish roots in warming soil, providing a full growing season for recovery before winter. Wait until the danger of frost has passed, as this can severely set back newly planted corms.
Alternatively, late fall, after the foliage has died back, is also suitable. Fall division, typically around October, works well because the soil is still warm enough for some root growth before the ground freezes. However, in colder climates or areas with consistently wet winters, spring division is safer, preventing corms from rotting in cold, saturated soil. The ideal timing depends on the local climate, but the goal is to divide when the plant is not actively growing.
Step-by-Step Division Process
The division process begins by carefully lifting the entire Crocosmia clump from the soil using a garden fork. To avoid damaging the corms, insert the fork well outside the clump’s perimeter, digging down at least 12 inches, as older plants develop deep root systems. Once lifted, gently shake or rinse away excess soil to expose the corms and root structure.
Crocosmia corms grow in vertical chains, with the newest and healthiest corms forming at the top of the stack. Separate these chains, which can often be gently pulled apart by hand. For very dense clumps, a sharp knife or spade may be needed to cut the mass into smaller sections.
Select the top two or three corms from each chain for replanting, as these are the youngest and most vigorous. Discard the old, shriveled, and spent corms at the base of the chain, as well as any corms that appear diseased or damaged. Before replanting, corms can optionally be dusted with a fungicide to protect against soil-borne pathogens.
Replant the separated corms immediately, setting them at the same depth they were previously growing (typically 3 to 4 inches deep). Proper spacing is necessary to delay future congestion. Plant the corms approximately 6 to 8 inches apart, giving them enough room to multiply and establish new chains.
Post-Division Care and Establishment
Immediate and thorough watering is necessary after replanting the divided corms to settle the soil around the roots and eliminate air pockets. The newly planted divisions require consistent moisture while they establish, especially during the first few weeks. Applying a layer of organic mulch helps to retain soil moisture and regulate temperature, minimizing stress on the transplanted corms.
It is common for newly divided Crocosmia to experience a period of reduced flowering in the first year following the procedure. The plant redirects its energy toward developing a robust new root system rather than producing blooms. Gardeners should expect the full vigor and prolific flowering display to return in the second year after division, once the corms have fully re-established themselves in the new location.