Nancy Brachey

Digging and dividing can help with new growth

This perennial coreopsis shows how roots spread to develop fresh, young plants that you can cut from the mother plant and replant in flower beds.
This perennial coreopsis shows how roots spread to develop fresh, young plants that you can cut from the mother plant and replant in flower beds. Observer file photo

When perennials fail to bloom as expected, gardeners are sometimes baffled at the cause. Often, the answer is quite simple: The plant is overgrown and requires renewal by digging, dividing and replanting its roots.

Most garden perennials are herbaceous, meaning fresh stems and leaves rise each spring, grow, bloom, then fade away, typically in late autumn. Some of our most popular plants, such as peonies, anemones, hardy sunflowers, daylilies, chrysanthemums, Shasta daisies, black-eyed susans, asters and hostas, grow from clumps that stay in the ground for years.

The amount of bloom tends to diminish eventually. That signals the moment for action, which can be done once plants end their bloom season, For fall-flowering plants such as mums and asters, it is better to wait for spring. But the spring and summer-flowering ones can be done this month and through the autumn.

The reason this works is that the plants tend to grow either by an expanding clump called a crown, such as daylilies, hostas, mums and asters, or by spreading roots that grow underground or near the surface, such as coreopsis, phlox and many kinds of daisies.

Clumps. Once you gently dig up the plant, it should be easy to see what type of underground plant you possess. A crown grows larger each year, and you should see baby plants called offsets attached to the perimeter. These are fairly easy to cut off from the mother plant. These young offsets are the making of your fresh planting.

Spreading roots. When the plant is dug up, these roots are clearly visible and tend to resemble an individual plant complete with crown and roots. Once cut from the mother plant, they can be reset and tended carefully. If the mother plant has not produced well, discard it and use the space for the new plants you just retrieved from the ground.

When replanting, give the plants fresh soil and space to develop. They may look tiny now, but should settle down through the autumn and be ready to grow next spring. Keep them watered as they settle in.

Woody plants. A third type of roots are made by woody perennials such as lavender, rosemary and candytuft. These tend to grow from a single stem and develop well over time without showing the bloom decline of plants whose crowns get old and crowded. Sometimes, these spread when a lower stem at ground level touches soil and take root. When this happens, you can gently dig up the new, little plant, cutting it from the mother plant and resetting it elsewhere. This will not harm the existing plant.

Nancy Brachey:

Ask Nancy

Q. I am getting older and find the getting up and getting down that is required for planting and tending increasingly difficult. It wears me out. What would help?

A. A small, lightweight plastic stool helps me. I use the one made by Rubbermaid and described as a step stool. I never stand on it, but I sit on it all the time to weed, plant and work in beds, pots and baskets. It weighs very little, doesn’t take much space and can be carried easily with one hand.