When perennials need to be divided, here's how to do it.
Courtesy of Karan Davis Cutler
Most hardy perennials that call out to be divided — plants that have lost vigor or have fewer or smaller flowers; plants that flop open at the center or have dead centers; plants that are overwhelming their neighbors — don’t have to be approached with kid gloves. A pruning saw and axe are two of my plant-dividing tools, along with a spading fork and shovel.
My first suggestion is to ignore the advice to divide perennials with two garden forks set back-to-back. Garden forks are great for digging — I wouldn’t be without one — but put an accent on “one.” Who owns two forks? (Well, I do, but I was sent them gratis when I worked as a magazine editor.)
But I’ve yet to see a gardener who can use two garden forks at the same time. Where that idea began I don’t know, and it’s repeated in the best of garden books. Don’t try it. Trust me on this one.
Begin by watering the plants a couple of days beforehand.
Then lift the plant with a shovel, spade, or garden fork, making sure you dig both wide and deep enough to get as many roots as possible. If it’s a cranesbill (Geranium spp.; see photo at left) you’re dividing, the task is easy, but I’ve bent steel shovels trying to lift large clumps of Siberian iris (I. sibirica).
Once out of the ground, the basic choices are either to pull the clump apart or to cut it apart.
In either case, don’t be tempted to replant huge sections, especially of plants that die out in their centers, such as Siberian iris, ornamental grasses, Shasta daisies (Leucanthemum superbum; see photo above), and bee balm (Monarda spp.). Small divisions reestablish far quicker and better than large ones.