Divide and Conquer

Dividing a hosta

Dividing a hosta

I’m not much on growing plants from seeds. I don’t have the patience or time to do it properly, so purchasing plants works better. However, I’m notorious for buying too large or mature for the space or more typically just planting without reading how big it will get some day causing crowding.

It’s okay because I love to gift splittings with family, friends and neighbors. I figure if these are my favorites aren’t they everyone’s? Typically I divide plants when I discover one plant choking out another or looking sickly because it’s wedged between an immoveable structure (the retaining wall) and a tree or shrub. This is not good gardening.

I know there are ways to keep my perennials healthy by dividing them properly. So… do what I tell you, not what I do.

You may respond that your gardens aren’t as crowded as mine (yes, you are a better planner than me), but there are still reasons to divide:

  1. It keeps the plants healthy. Many perennials grow quickly, forming large clumps. If you don’t divide them regularly years, the clumps die in the middle, leaving an ugly hole.
  2. Some plants are prone to disease and insect infestation if not kept in tip-top shape.
  3. Overcrowded perennials have fewer and/or smaller flowers than their well-spaced and divided counterparts.
  4. If not kept in check, they can overwhelm less aggressive neighboring plants (don’t even ask me about my bugleweed!).

Spring and fall are the best seasons to divide because the plants will recover better in cool, moist conditions. I’ve divided in the summer with success, but again do I as I recommend not as I do.

You’ll know a plant is ready to divide when it is large enough that you can get 2-3 large clumps out of the original. The basic steps are:

  1. Dig the entire clump. It helps if you do this after a good rain so the soil is softer. Be careful of the root system so it stays fully intact. Shake or wash off the excess soil carefully.
  2. Separate individual clumps. Each clump needs to have sets of leaves and roots.
  3. Replant promptly and at the same depth as before. Water well.

Dividing iris is a little different. The rhizomes grow shallow with the tops above soil in some cases. Dig up the clump after its done blooming. Divide into groups of 3-4 rhizomes (leaves, bulb, and roots). Trim the leaves back to a third their original length and then store in cool, dry place until you are ready to plant. You may transplant right away but it isn’t necessary. I left a bunch in a paper bag over the winter once and still saw success the following year. Don’t worry about the leaves yellowing, the plant is just going dormant. The biggest issue is to make sure to watch for fungus, mold or disease. Don’t replant rhizomes that will make all their neighboring plants ill.

Most perennials benefit from being divided every few years, there are a few that don’t such as:

  • Baptisia
  • Bleeding heart (Dicentra)
  • Butterfly weed (Asclepias)
  • Christmas rose (Helleborus)
  • Gas plant (Dictamnus)
  • Lavender (Lavandula)
  • Oriental poppy (Papaver orientale)
  • Peony (Paeonia)

The ones that truly appreciate the 3-4 year rule include:

  • Astilbe
  • Bee balm (Monarda)
  • Black-eyed Susan (Rudbeckia)
  • Daylily (Hemerocallis)
  • Hosta
  • Phlox
  • Purple coneflower (Echinacea)
  • Siberian iris (Iris sibirica)

Divide these every other year:

  • Aster
  • Blanket flower (Gaillardia)
  • Clustered bellflowers (Campanula glomerata)
  • Coreopsis
  • Lamb’s ears (Stachys)
  • Yarrow (Achillea)

Details for this blog may be found here


About Kary Beck

Mother and wife, gardener, wine enthusiast, avid online bargain hunter, and owner of two black-and-tan cocker spaniels.
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