Dividing Perennials – The Basics
If your once-robust Hosta, Iris, Shasta Daisy, Creeping Phlox, or Peonies looked weak or had puny flowers this season, it may be time to divide the clumps. Clumps that have no middle flowers and seem more like a ring than a dome need dividing. Actually, any 3-4 year old perennial clump can benefit from division.
In mid-August through early September, soils are warm but evenings are cooler, a perfect time to divide perennials. Like when you plant, divide plants on a cloudy day, in the morning or early evening. New plantings and divisions now will grow with less heat-stress and be established before winter cold sets in.
The supplies you’ll need:
- Large-oversized clump of perennials – We’ll stick to those that bloom in the Spring or early summer. While planting any perennial is great right now, plan to limit division to Hosta, Iris, Shasta Daisy, Hellebores, Creeping Phlox or Peony – or similar. Why? Well, you only have so much time and these plants have completed their flower cycle so energy will be spent on spreading roots into a new area and setting bloom for next year.
- Water- Your overgrown clumps need to be well-watered before you begin. Give them a deep soaking before you gather your other materials or prepare a new garden location. Then water again right before you lift them out of the ground. Drought-stressed divisions will not take to a new location very well.
- Bucket or wheelbarrow to rinse and hold divisions in water.
- Garden Fork or Perennial Spade – This is the tool you use to cut around the clump and lever it out of the ground without disturbing its garden companions!
- Sharp, long knife– Some clumps are so tightly packed there is no way you can break it apart. You’ll use the knife to slice it into chunks from top to bottom.
- Tarp or handy spot to make your mess – A tarp will hold the soil and plant pieces making cleanup easier.
- Compost and/or Potting Mix – Refreshed soil improves the health and growth of the old clump and new divisions.
- New Planting Location or Pots to Share– New planting locations or pots should be identified, prepared with compost or fresh potting soil and well watered, ready to receive the division.
Ready, Set, Divide
- Water your clump deeply then gather your other materials while allowing the water to seep in.
- Dig out your new planting hole. You’ll need to adjust this once you have your clump so the hole is twice as wide as your division but no deeper than the clump’s roots are long. If potting, choose pots that will be about 2 inches wider than the division and the same depth as your clump’s roots are long. Fill pots about ½ full with potting soil.
- Water your clump again.
- Cut in your spade or fork at the drip line of your clump (where water would drop off the outer-most leaves) in a complete circle, gently prying up the clump by loosening the roots about 10 – 12 inches below the soil level.
- Confirm where the soil level meets your successful perennial, how much plant is below and how much above the soil level? You’ll need this information when you replant.
- A- Perennials that spread via long roots with multiple eyes: Rinse clumps of Hosta, Hellebores or Peony in your bucket or wheelbarrow. Lay out the clump on your tarp and imagine slicing through it from above, like quartering a pie. Use your sharp knife to slice through the clump from top to bottom. Each division should have leaves, stems, and roots connected from top to bottom and roughly 6-10 roots each.
B- Perennials that spread via tuberous roots along the soil surface: Iris, Creeping Phlox, perennial Geranium and Daylily should be rinsed and then spread out on the tarp and broken or cut apart into fans or stems of leaves with 2-3 roots each.
- Inspect the root health of your divisions. Cut out any roots that are woody and dead or that appear mushy and bruised.
- Return your divisions to the bucket of water while you adjust the depth of your new planting locations.
- Fill the original location with compost in preparation for a much smaller clump. Replant using the instructions below.
- A- Perennials that spread via long roots with multiple eyes: having loosened and amended the soil to the depth of your clump’s roots, form a cone in the hole or pot so you can rest the division on the narrow top and fan the roots around the cone. Make sure the cone lifts the plant to its original growing level. Perennials planted too deeply may experience stem rot. Better too shallow than too deep. Fill the planting hole with your topsoil and compost mix to the proper soil level, Water thoroughly. Mulch to help retain moisture.
B – Perennials that spread via tuberous roots along the soil surface: Return your top soil/compost mix to the new growing hole or pot within about 3 inches of the soil level. Set the roots flat on the mix with the fans upright. Fill around the roots and on top with soil mix until you reach the surrounding soil level, packing the soil gently but firmly around the fans/stems. Water thoroughly and mulch to retain moisture.
- Check daily and keep the soil moist around your fresh plantings.
- Potted up divisions should be kept in a partial sun location to help retain moisture. Eastern – morning – light is best. Share potted perennials with friends soon so the plants can get accustomed to a new location before winter.
- New leaf growth indicates that the plant is rooting successfully into place!