Why Some Perennials Need Division and Others Don't: The Gardener's Guide

Tips for Dividing Perennials for Plant Health and to Expand Your Garden

As gardeners, we often ponder the intricacies of plant care, especially when it comes to perennials. One common question is, "Why do some perennials need to be divided while others don't?" As with many gardening practices, there's both art and science involved. Dive in with us to learn more about perennial division.

The Benefits of Dividing Perennials

When you divide perennials you’ll provide them with the best growing conditions, and you know what that means for you? More flowers!

Vigor and Health: Over time, certain perennials can become overcrowded, leading to a decrease in bloom quality and plant health. Dividing them rejuvenates the plant, giving them more space and better access to nutrients.

Propagation: It's a great way to multiply the number of plants you have without buying more. If you have a favorite perennial, dividing can help spread its beauty to other parts of your garden.

Disease Control: Overcrowded plants are more susceptible to diseases. By dividing them, you can reduce the risk of disease spread.

The Science Behind the Need for Division

Not all perennials grow the same way and so do not require the same care. Here's a quick breakdown:

Clump-forming perennials, such as daylilies or hostas, grow outward from the center. Over time, the middle may die out, leaving an unattractive, donut-shaped hole. These benefit most from division.

Spreading perennials, like mint or bee balm, send out runners or rhizomes. These can become overgrown if not kept in check. Division helps control their spread.

Taproot perennials, like columbines or oriental poppies, grow from a central, thick root. These typically don't need division for the health of the plant, and doing so can be challenging.

What Happens If You Don't Divide?

Just like soil nutrients and pest control, you’ll have the most success with gardening when you provide your plants with ideal growing conditions. For clump-forming perennials that means dividing them. The frequency of division varies. Check the information below to know how often your garden favorites need division, whether for healthy blooms, to control spread, or if they don’t require division at all.

  • Reduced Flowering: Overcrowded plants often produce fewer and smaller blooms.
  • Vulnerability to Disease: As mentioned, tightly packed plants have reduced airflow, leading to fungal diseases.
  • Depletion of Soil Nutrients: Competing roots can quickly exhaust the nutrients in the soil.
  • Unruly Growth: Some perennials can overrun other plants if not divided, altering the aesthetics and balance of your garden.

The Bottom Line

While many perennials benefit from periodic division, it's essential to understand the specific needs and growth patterns of the plants in your garden. A well-maintained garden is not only more aesthetically pleasing but also promotes healthier plant life.

To maximize the number of blooms, the size of blooms, and to optimize your garden's health, divide perennials that benefit from the practice because when done correctly and at the right time, can yield abundant rewards.


Common Perennials that Benefit from Dividing

Perennial Divide Every: Special Requirements:
Hostas 3-5 years Divide when the plant is dormant. Water well after replanting.
Daylilies (Hemerocallis) 3-5 years Divide when the flowers have finished blooming. Replant immediately and water thoroughly.
Iris 3-4 years Divide after flowering. Cut leaves back to about six inches and replant rhizomes just below the soil surface.
Peonies 10-15 years Divide in early fall. Plant with the eyes (buds) no more than 2 inches below the soil surface.
Sedum (Stonecrop) 3-4 years Divide in early fall. Replant in well-drained soil.
Asters 2-3 years Divide in early fall. Plant in a sunny location with well-drained soil.
Chrysanthemums 2-3 years Divide in early fall. Plant in full sun and water well.
Coneflowers (Echinacea) 3-4 years Divide in early fall. Plant in a sunny location with well-drained soil.
Ornamental Grasses 3-5 years Divide in early fall. Replant in a location with full sun to partial shade.
Yarrow (Achillea) 2-3 years Divide in early fall. Plant in full sun with well-drained soil.
Shasta Daisy 2-3 years Divide in early fall. Plant in full sun and water well.
Coral Bells (Heuchera) 3-5 years Divide in early fall. Plant in partial shade with well-drained soil.

NOTE: Specific requirements for dividing and planting may vary depending on your local climate and soil conditions. Consult your County Extension Office to understand the specific needs of plants in your area.


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