Dividing Perennials

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Dividing perennials means digging up and splitting plants using varying techniques to increase your plant stock and improve the health, vitality, and blooming capacity of your plants.

 

How do I know if a plant needs dividing?

You can tell a plant needs to be divided if the plant dies out in the center of the crown, if the crown raises up out of the ground, or if the plant stops or dramatically slows down blooming.

 

When should perennials be divided?

If a plant blooms in the spring or summer, divide in the fall.

Early fall bloomers can also be split in late fall after blooming.

If a plant blooms in the fall, divide in the spring (examples are mums, asters, and ornamental grasses)

Divide plants when weather is cool and damp: in CT, April to late May or mid-September to late October.

 

How to I divide perennials?

Dig the entire plant out of the ground, place on a tarp; never try to take a small piece of a plant out of the ground and leave the rest in—this is a great way to kill a plant!

Once out of the ground, cut back bulk of foliage by at least 1/3, but no more than 2/3.

Look for natural separations in the crown—divide along these lines using various degrees of force (e.g.: trowel, sharp knife, edging spade, two pitchforks back-to-back, saw, axe). You may be able to make multiple divisions from each plant you dig up. If the center is dead, discard it.

Prepare soil for replanting by turning the soil over, removing rocks and weeds. Amend with compost. Add organic granular fertilizer (such as Pro Gro or Sustane). Sprinkle Myco-Bio to encourage soil life and feeder root growth. Plant the crowns at the same depth as before.

 

Then what?

 Mulch thickly around crowns to keep soil warm and encourage rooting. Water well and deeply for first two weeks if there aren’t deep soaking rains.

Don’t expect a lot of top growth. In fact, the tops may continue to die back. The goal in fall planting is to have good ROOT GROWTH.

Apply a winter mulch of cut evergreen boughs over the crowns of the fall divided plants in early winter, after soil has frozen. The goal is to keep the soil frozen and prevent heaving of crowns. This is very important as climate change means that winter temperatures can go from warm to freezing cold in a few hours. This can heave the plants up out of the ground and expose their crowns and root systems to deadly cold temperatures.

 

Division Frequency

 

Plants that should be divided every 2-3 years

Achillea

Alchemilla

Aster

Astilbe

Campanula persicifolia

Dendranthema (in spring)

Helenium

Hemerocallis- repeat blooming types

Heuchera

Iris, German/bearded (special note: divide in July/early August when leaves stop growing)

Leucanthemum

Monarda

Phlox paniculata

Primula

Stachys byzantine (lamb’s ears)

Stokesia

Veronica spicata

 

Plants that should be divided every 4-5 years

Bergenia

Dianthus

Digitalis grandiflora

Echinacea

Geranium (cranesbill)

Helianthus

Heliopsis

Hemerocallis (non-repeat bloomers)

Iris, Siberian and Japanese

Lamium

Pulmonaria

Rudbeckia

Salvia

Scabiosa

Sedum (upright types)

 

Plants that usually don’t need dividing

Asclepias

Baptisia

Dicentra spectabilis (old fashioned bleeding heart)

Gypsophila

Helleborus

Hosta

Paeonia (peony)

 

Special note: Only divide oriental poppies (Papaver orientale) in the fall after they have grown new leaves after summer dormancy. Never try to divide them in the spring.

 

In an effort to provide horticultural information, these educational documents are written by Nancy DuBrule-Clemente and are the property of Natureworks Horticultural Services, LLC.  You are granted permission to print/photocopy this educational information free of charge as long as you clearly show that these are Natureworks documents