Is your garden overflowing with perennial flowers this summer? Perennials can be divided to control size, to rejuvenate a tired-looking plant or to give plants away to those friends and neighbors and even family.
Most perennials can be successfully divided in fall or early spring. There are a few that are best divided in early summer and a few that can be divided in late summer/early fall. It is not a good idea to divide plants in the heat of summer so wait for a cool day — not so difficult to find in our neck of the woods! It is also best to wait until they have finished blooming.
It is a good idea to water the soil around any plants you will divide prior to disturbing them.
To divide perennials, the ground around the plant should first be gently worked with a fork or shovel, then dig at least 6 to 8 inches deep alongside the plant to ensure a good root ball is formed. Gently lift the plant out of the ground, and place it on a tarp or in a wheelbarrow.
The clump can be divided into two to four parts with a shovel.
Each part should be planted as soon as possible and watered in well. Root systems that are difficult to separate can be cleanly cut with a sharp knife. The roots will regenerate where the cuts are made.
Early summer dividers
•Bearded iris (Iris germamica) and Siberian iris (Iris siberica) — Divide after the blooms fade, but a month or so before first frost so plants have a chance to get established.
Late summer/early fall dividers
•Bleeding Hearts (Dicentra) — Divide after they go dormant. The roots are brittle, so be sure you get a big enough piece when you divide.
•Daylilies (Hemerocallis) — Use a garden fork to lift the clump from the ground. Start by placing the fork in the ground 6 to 12 inches away from the base of the plant, and gently push down on the handle to pry the clump up and out of the soil. Work around the root ball, repeating this process, until the roots are freed.
Daylilies can often be pulled apart by hand.
•Lungwort (Pulmonaria) — Use a knife to split the lungwort instead of just pulling it apart.
•Garden phlox (Phlox paniculata) — Each division should consist of three to five vigorous shoots, with roots attached.
These lovely flowers will soon make a robust addition to your or a lucky friend’s garden.
For more information about perennials and dividing plants please contact the Garden Hotline at (206) 633-0224 or e-mail help@gardenhotline.org.
SHERI HINSHAW is an environmental educator for the Garden Hotline at Seattle Tilth (seattletilth.org).
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