Gardening

Plant Division: Free Plants-Now Is Your Time

Plant Division: Free Plants-Now Is Your Time

Plant Division

Photo Compliments Of Bob Gutowski

Overcrowded plants struggle to compete for nutrients and water while restricted air circulation creates conditions favorable for pests and diseases. Plant division is a useful technique to help keep your perennial border neat, healthy and in peak bloom.

When

Generally, it is best to divide spring and summer blooming perennials in the fall, and fall bloomers in spring. Dividing the plant when it is not flowering will allow it to drive all of the energy to root and leaf growth. Fall division should take place between early September and mid-to late October. Allow at least four to six weeks before the ground freezes for the plants to become established in areas where ground freeze is the rule. If you divide in the spring, allow enough time for roots to settle in before hot weather. Spring division is ideally done in the early spring as soon as the growing tips of the plant have emerged. Spring divided perennials may bloom a little later than usual. Try to avoid doing this on sunny or hot days.

How Often

You should divide perennials every three to five years. Some perennials such as chrysanthemums and asters may need to be divided more often; every one or two years or they will crowd themselves into non-flowering clumps of leaves and roots. Bleeding hearts and peonies may never need to be divided unless you want to increase your stock. The internet is a good source of specific plant information.

Signs that perennials need dividing are flowers that are smaller than normal, centers of the clumps that are hollow and dead, or when the bottom foliage is sparse and poor.

Guidelines For Plant Division

1. Timing Is Important

Don’t wait until a plant has become decrepit or to large to divide. The rule of thumb is when it looks its best; go ahead and divide it. Watch for early signs of trouble: when the center of the plant has smaller leaves, fewer flowers, and weaker blooming stalks, or when the plant runs out of growing room on its edges and has nowhere to go but into neighboring plants.

2. Start at the drip line

Lifting a perennial out of the ground with minimal root damage is not difficult. The process begins by digging at the drip line. The roots will generally extend that far, so digging there lets you lift the plant with most of its roots intact. Dig a trench around the clump, cleanly severing any roots. Use the shovel to cut at an angle down and under the clump from various points around the outer edge. You can now lever the plant out of the hole. For large, heavy plants, you may have to first dig the trench, and then slice straight down through the center of the plant as if it was a pie, halving or quartering the clump before under­cutting and lifting it.

In early spring, I divide while the new growth is still low to the ground, so the handling of stems is not usually an issue. In summer, I might tie stems together before lifting the plant to avoid damaging them during the digging. In fall, I usually cut plants back before digging them for division.

3. Divide In Cool Weather

I divide when the soil is warmer than the air for at least a 24-hour period. That would be just before peak daffodil season in spring and in early fall right after the nights become cool. This allows roots of the new divisions to grow while the tops stay low, out of the sun and wind.

My preference is to divide in the fall rather than in the spring because the plants have more time to set new roots before putting more energy into general plant growth. I divide fall bloomers in September or October.

4. Keep Roots Cool And Moist

Fifty percent humidity and 50°F are the ideal conditions for holding divisions until you can get them back into the ground. Store them in a bucket or box in a cool shaded place, such as a garage, and cover them with newspaper to retard moisture loss. Sprinkle water to dampen the newspaper if the roots seem to be drying during a “hold” period. If a plant division does dry a bit soak them in a bucket of water for about an hour before replanting.

5. Replenish With Organic Matter

If you remove a wheelbarrow full of perennials, then you should put a wheel­barrow full of compost back into that site before replanting to renew the soil, stay ahead of pest problems, and maintain fertility. Without additions, the plants will not have the advantage of renewed, fertile soil and the bed will settle after planting. This also puts the plants at a disadvantage in terms of drainage and air circulation.

6. Use Vigorous Sections First

After dividing, replant pieces that are, at most, 20 to 25 percent of the original clump. Smaller sections grow more vigorously and tend to produce stronger, longer-lasting blooms. Dividing a hosta, for example into pieces with about seven growing points will yield the best results.

7. Take Extra Care When A Plant’s In Bloom

I have divided plants when blooming. The understanding is that plants in bloom may not be capable of growing as many new roots as quickly as nonblooming plants. I’ve done this and I haven’t lost any divisions yet. I would say it is not the best practice.

8. Keep Only The Healthiest Pieces

If you wait until a perennial is declining, has a dead center, or has succumbed to pest problems because it has become crowded and weak, be sure to replant only the healthiest pieces. Usually these are the outside sections. Watch for discolored stems and eroded crowns and roots.

9. Spread Out Your Divisions

Place a division into a hole that is at least as wide as its roots when spread out. Spread out the roots wide and down over a mound of soil at the bottom of the hole. In the next growing season, the top of the plant will be as wide as the roots are at the time of planting. Ensure that when you spread out the roots they don’t overlap and compete with the other divisions.

A large, vigorous plant with thick intertwined roots should be forcefully separated using a digging fork. Divide the plants into clumps of three to five vigorous shoots each. Small or weak and woody divisions should be discarded. Discard the center of the clump if it is weaker than the outside edges.  If your perennial has a clumping root system that originates from a central clump with multiple growing points you can use a heavy, sharp knife to pry apart thick fleshy crowns and roots. This group includes astilbes, hostas, daylilies and many ornamental grasses. Keep at least one developing eye or bud with each division. If larger plants are wanted, keep several eyes.

Rhizomes are stems that grow horizontally at or above the soil level. Bearded irises are a common example. You can divide irises any time between a month after flowering or until early fall. Inspect rhizomes for disease and insect damage. Damaged rhizomes should be trimmed and treated, or discarded if too badly damaged. Iris divisions should retain a few inches of rhizome and one fan of leaves, trimmed back halfway. Replant with the top of the rhizome just showing above soil level.

Dahlias are an example of perennials with tuberous roots. The tubers should be cut apart with a sharp knife. Every division must have a piece of the original stem and a growth bud attached. After division they can either be replanted or stored for spring planting.

If the root is very large, or tight and tangled, you can raise the clump 1 to 2 feet off the ground and drop it. This should loosen the root mass, and you can pull the individual plants apart. This is not a good method for plants with brittle roots such as peonies.

Plants that have tough, vigorous root systems (agapanthus, red-hot pokers and ornamental grasses) you may have to be divided with a shovel, saw or ax. You can also vigorously hose off soil to make the root system easier to work with.

Plant Division Timing Information

Divide In Early Spring Every 1 to 3 Years

  • Aster
  • Beardtongue (Penstemon)
  • Beebalm (Monarda)
  • Carnation (Dianthus)
  • Common Sundrops (Oenothera fruticosa)
  • Coralbells (Heuchera)
  • Cornflower (Centaurea)
  • Delphinium
  • Fernleaf Bleeding Heart (Dicentra eximia) Foamflower (Tiarella)
  • Garden Mums (Dendranthema x grandiflora)
  • Obedient Plant (Physostegia)
  • Painted Daisy (Tanacetum)
  • Shasta Daisy (Leucanthemum)
  • Spiderwort (Tradescantia)
  • Tall Phlox (Phlox paniculata)
  • Tickseed (Coreopsis)
  • Yarrow (Achillea)

Divide In Early Spring every 3 to 5 Years 

  • Astilbe
  • Bellflower (Campanula)
  • Blanket Flower (Gaillardia)
  • Catmint (Nepeta)
  • Coneflower (Rudbeckia)
  • Daylily (Hemerocallis)
  • Gay Feather (Liatris) Gooseneck Loosestrife (Lysimachia clethroides)
  • Jacob’s Ladder (Polemonium)
  • Mallow (Malvia)
  • Sea Thrift (Armeria)
  • Speedwell (Veronica)
  • Yellow Loosestrife (Lysimachia punctata)

 Divide in Early Spring Every 5 to 10 Years

  • Cranesbill (Geranium)
  • Goatsbeard (Aruncus)
  • Hosta
  • Japanese Anemone (Anemone x hybrida)
  • Lady’s Mantle (Alchemilla) Lungwort (Pulmonaria)
  • Meadow Rue (Thalictrum)
  • Meadowsweet (Filipendula)
  • Oxeye (Heliopsis)
  • Siberian Iris

Divide In Late Summer or Early Fall

  • Asiatic Lily
  • Bearded Iris
  • Daylily (Hemerocallis)
  • Jacob’s Ladder (Polemonium) *Peony (divide infrequently)
  • Tall Phlox (Phlox paniculata)
  • Siberian Iris

Do Not Divide

  • Baby’s Breath (Gypsophila)
  • Balloon Flower (Platycodon)
  • Bugbane (Cimicifuga)
  • Butterfly Weed (Asclepias)
  • Clematis
  • Evening Primrose (Oenothera missourienis) False Indigo (Baptisia)
  • Flax (Linum)
  • Gentian
  • Lupine
  • Monkshood (Aconitum)
  • Russian Sage (Perovskia)

Divide Only to Popagate 

  • Bugbane (Cimicifuga)
  • Globeflower (Trollius) Yucca

Additional Information Sources

Plant Division-Cornell University

Plant Division-Washington State University

If this information was helpful please pass it to a fellow gardener.

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8 Comments

  1. I love dividing plants and having free plants to give or swap with friends.
    bridget recently posted..As Autumn berries ripen…My Profile

    • We have a big plant swap in the spring and in the fall. This past spring was my first time and it was amazing. I have about two dozen plants that I have from starts and divisions…I am prepared to participate this time around.

  2. Good Information. There’s always something to do ina garden!

  3. Great tips!

  4. Good advice Charlie. We have a plant sale each spring so plenty of my perennials get split for that in September. It’s always good to swap plants with neighbours too and the plants all benefit from it.
    Pauline recently posted..August Flowers. GBBD.My Profile

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