Divide & Conquer: When & How to Divide Perennials

Does your garden look like a wild jungle these days, with overgrown perennials fighting for space and sunlight? Knowing when and how to split perennials will keep them healthy. Plus, it’s a great way to multiply your plants for free!

Perennials need space to spread, so expect to divide them every three to five years. That’s when they’ll have new shoots on the outside with little growth towards the center, or when they’re producing smaller flowers and fewer leaves.

Grab the right tools for the job:

  • A sharp spade and sturdy garden forks
  • Hand pruners or a sharp, non-serrated knife

You don’t have to divide fall-flowering perennials in the spring and spring-flowering plants in the fall. You can divide spring-flowering plants right after they blossom – this way, they’ll settle into their new home all summer.

You can also divide most plants in late summer or early fall if they’re still actively growing; just finish the job at least a month before the first hard frost, so that divided plants can grow new roots into soil that’s still warm. Perennials like peonies, astilbes, and tall bearded irises have fleshy roots, and should only be divided in the autumn, because they use up lots of energy in the spring and need the summer to recover.

Got invasive plants including goutweed, carpet bugleweed or lily-of-the-valley? Keep them under control by dividing them every year. Be sure to get every bit, because leftover roots can quickly take over the area again.

Step-by-step tips:

  • Choose a cool, cloudy day if possible, and water the area before digging in; the moisture will help the plants recover from the stress of dividing and replanting.
  • Depending on what kind of roots your plant has, you’ll use slightly different techniques:
    • For roots that form clumps – such as hostas and coneflowers – sever the connection between sections, and get a piece that has at least three growing points.
    • For plants with roots just below the surface of the soil – like bee balms or black-eyed Susans – cut between any of the stems.
    • Divide perennials with taproots, including Oriental poppies and balloon flowers, by slicing down the length of the root with a knife.
    • Underground running roots, such as ones on hardy geraniums, feature suckers. Cut them away or dig up the main plant and cut a piece off.
    • Stems of woody perennials like lavender usually rest on the ground, so make a new plant by cutting between the mother plant and a rooted stem.
    • For large, fibrous plants like daylilies, loosen the soil around and underneath the plant. Insert two forks back-to-back in the center and push them in opposite directions.
  • Choose only the healthiest shoots to replant. Prepare the planting holes with compost mixed into the existing soil, and don’t crowd in the new additions. Water deeply. Don’t forget to mulch!
  • Be patient! Some transplanted perennials might take awhile to grow large enough to bloom again.

Photo Credits:
Couple in garden: auntjojo via Compfight cc

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