12 Perennials You Should Always Divide to Keep Them Blooming Year After Year

Iris

Certain members of the iris family (Iridaceae), like iris 'Albo Variegata,' need to be divided to maintain vigor and prevent overcrowding, says Kelly Funk, president & CEO Jackson & Perkins. Overcrowding could cause the plant to stop flowering and makes it more susceptible to root rot.

• Zones: 3 to 10
• Size: 34 inches tall x 18 inches wide
• Care requirements: Full sun to partial shade; well-drained, normal soil
  

Coneflowers

Coneflower varieties (Echinacea) should be divided every four to five years to promote healthy growth and create new plants, says Funk. If you don't divide coneflowers, they can become too dense, reducing flowering and attracting pests.

• Zones: 4 to 9
• Size: 22 to 24 inches tall x 18 to 20 inches wide
• Care requirements: Full sun; withstands a range of soil conditions

Lamb's Ear

Lamb’s ear (Stachys byzantina) is a beautiful ground cover with thick grey-green leaves and clusters of lavender flowers. Over time, the dense mat can lead to rot due to the leaves desiccating. This can cause the center of the plant to become hollowed out, says plant expert Adrienne Roethling. Dividing this plant every two to three years can prevent this from happening and ensure the plant stays healthy.

• Zones: 4 to 8
• Size: 5 to 6 inches tall x 12 to 24 inches wide
• Care requirements: Full sun; loamy, well-drained soil

Black-Eyed Susan

Black-eyed Susans (Rudbeckia) should be divided in order to control spreading and encourage healthier blooms. "Limited spacing leads to powdery mildew and reduced flowering," says Funk. "Divide every three to four years for the best appearance."

• Zones: 4 to 10
• Size: 14 to 16 inches tall x 14 to 16 inches wide
• Care requirements: Full sun; withstands a range of soil conditions

Bee Balm

Aim to divide bee balm (Monarda) every two to three years. Doing so helps control mildew, prevents spreading, and rejuvenates the plant, says Funk.

• Zones: 4 to 9
• Size: 12 inches tall x 12 inches wide
• Care requirements: Full sun to partial shade; well-drained, normal or loamy soil

Yarrow

Varieties of yarrow (Achillea), such as 'Little Moonshine,' should be divided every two to three years to prevent overcrowding and for plant propagation, says Funk. Compacted clumps of yarrow inhibit airflow and cause weaker stems that are prone to flopping.

• Zones: 4 to 9
• Size: 9 to 12 inches tall x 10 to 12 inches wide
• Care requirements: Full sun to partial shade; well-drained, normal, loamy, or poor soil

Astilbe

Varieties of astilbe (Astilbe spp.), like 'Washington,' need to be divided every two to three years to prevent overcrowding and rejuvenate growth, says Funk. Dense crowns restrict new growth, which can limit flowering and increase the chances of root rot.

• Zones: 3 to 8
• Size: 13 inches tall x 19 inches wide
• Care requirements: Partial shade to full shade; normal or loamy soil

Hosta

Hostas (Hosta spp.) are popular foliage plants that produce a tall flower stalk in late spring through summer. While hostas are resilient plants that can thrive just about anywhere, they benefit from being divided now and then, says Roethling. Over time, these plants may experience loss in size and vigor, which division can help counteract.

• Zones: 3 to 9
• Size: 12 to 24 inches tall x 12 to 24 inches wide, though some varieties may be larger
• Care requirements: Full to partial shade; moist, well-drained soil

Peonies

Peonies (Paeonia ssp.) come in many forms, but herbaceous peony will benefit from being divided every few years during fall. "Over time, the stems and roots grow all gnarly and eventually choke out the buds and center of the plant," says Roethling. "This will often lead to root rot." In addition to root rot, the blooms will look lackluster and the leaves become prone to leaf or stem blight.

• Zones: 3 to 8
• Mature size: 1 to 3 feet tall x 1 to 3 feet wide
• Care requirements: Full sun; well-draining soil; water moderately

Aster

Aster (Symphyotrichum ssp.) is native throughout North America and often grown for its ability to withstand hot, dry conditions. Its lavender-blue daisy-like flowers are prolific throughout summer and into fall. One downside is that these plants can quickly take over your garden. To keep aster in check, consider dividing it every few years.

• Zones: 4 to 9
• Size: 1 to 6 feet tall x 1 to 2 feet wide
• Care requirements: Full sun to part shade; moist, well-drained soil
  

Carnations

The most common form of dianthus (Dianthus ssp.) that gardeners grow is 'Cheddar Pink,' a ground cover with fragrant blooms. Flowers come in shades of red, pink, purple, and white, says Roethling. Sometimes, cheddar pink hollows out in the center from poor drainage, lack of shade, or nutrient deprivation. Dividing this plant in the fall can help avoid these issues.

• Zones: 3 to 9
• Size: 1 to 6 feet tall x 1 to 2 feet wide
• Care requirements: Full sun to part shade; moist, well-drained soil

Daylily

Daylily (Hemerocallis ssp.) can take a beating and still maintain its beauty. "They are one of those landscape plants you see along highways or in parking lots," says Roethling. "The foliage emerges in spring, with thick green blades giving way to stalks of tubular flowers in summer."

Although they're resilient plants, daylilies may become leggy and produce smaller flowers over time. "They always respond well to dividing," says Roethling. "Dig the plants and sever the roots until you have as many divisions as you want."

• Zones: 3 to 9
• Size: 1 to 6 feet tall x 1 to 2 feet wide
• Care requirements: Full sun to part shade; moist, well-drained soil