Flower Gardening

Dividing Perennials During the Fall

By Jean Starr

Fall Dividing

Fall is a great time to divide plants that grow and bloom in early to mid-summer, including Astilbe, Siberian iris Veronica, and Salvia.

Siberian iris can take at least two years after planting before they bloom well, especially if the original clump consists of fewer than three growing points. A healthy Siberian iris should reach its peak in its third season, and continue growing well its fourth and fifth seasons. Beyond that, you will not want to delay the division process, because that is the point at which the beautiful clump turns into a gristly root mass that sends up a few meager blooms. If you choose to divide your Siberian irises in the fall, cut leaves back to around six inches to make it easier to handle, and dig up the entire clump before cutting apart only the healthy tissue.

If dividing an overgrown Siberian iris is a trek up the side of a mountain, then separating perennials like Astilbe, Salvia, and Veronica is a walk in the park. Dig gently around the plant at least four to six inches beyond its outer crown, and it should easily come out of the ground. Shake the soil away and you’ll see several little clumps connected by roots that you can easily untangle to separate and replant.

Bulbs

If you have spring blooming bulbs growing near plants that you will be dividing, use a digging fork. This lessens the chance that you’ll damage the bulbs. If the soil is dry and difficult to dig, give the area surrounding the plant a good soaking first. Try to perform digging tasks during the cooler times of day or on a day that is cloudy in order to lessen the stress on the plants’ roots.

There are no hard rules about dividing plants in the fall. But there certainly are advantages. As fall progresses into winter, days are shorter, so the ground has more time to cool off, and moisture remains in the soil longer. It’s cooler, so the plants aren’t stressed from the heat.

For some plants, it just makes sense. This is the case for lilies—those that grow from bulbs, that is. Most have finished blooming by early August, and have been soaking up nutrients through their stems, which might as well have little signs on them saying, “dig here.”

Lilies are some of the easiest perennials to dig, provided you dig deep enough. I can’t count the number of times I’ve come up with just a stem, leaving the bulb in the ground. Once, I dug up a patch of lilies to make room for a raised bed that contained more than two feet of soil. I had apparently missed one. The following year I had a lily that grew from its position three feet underground.

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