Dividing Perennials 411

Take the guesswork out of dividing perennials by learning the basics.

©2009, Dorling Kindersley Limited

Photo By: Julie Martens Forney

©2008, Dorling Kindersley Limited

Photo By: Julie Martens Forney

Photo By: PerennialResource.com

Photo By: Julie Martens Forney

Photo By: Image courtesy of Johnny’s Selected Seeds.

©2008, Dorling Kindersley Limited

©2011, Dorling Kindersley Limited

©2011, Dorling Kindersley Limited

Photo By: Image courtesy of Johnny's Selected Seeds.

Photo By: Julie Martens Forney

Mixed Perennial Planting

Growing perennials is one of gardening’s great pleasures. By mixing flower and leaf colors and selecting plants with different flowering windows, you can orchestrate a symphony of bud and bloom that looks great year-round. As perennials thrive, most will reach a point that they need dividing. For many gardeners, fear of dividing ranks right up there with fear of pruning. Learn what you need to know to succeed with dividing perennials.

Fibrous Root System

Different kinds of perennials have different types of root systems. Understanding the roots is one key to success with dividing. Many perennials have a fibrous root system, like this alpine strawberry. You’ll also find fibrous roots in anise hyssop, black-eyed susan and coral bells. With a fibrous-rooted plant, division is simply a matter of unearthing the clump and literally cutting it into pieces.

Plants That Form Offsets

Some plants produce offsets, small plants that grow near the base of the mother plant. Many succulents form offsets, including agave. Can you see the smaller plant to the lower right and upper left side of this variegated Caribbean agave? To divide this plant, you want to slice through the connection point between the main plant and the offset, which should have roots of its own. Other plants that form offsets include yucca, hosta and hens and chicks.

Perennials With Rhizomes

A rhizome is a type of fattened stem that grows along or above soil. Bearded iris are the most common example of a perennial that grows by rhizomes. Blackberry lilies and wood violets also form rhizomes. To divide plants that have rhizomes, dig up the rhizome and slice cleanly through it. Each new division should have a growing point with leaves and a section of rhizome that’s several inches long.

Tap-Rooted Perennials

Plants that form tap roots, like butterfly weed, balloon flower, false indigo and Oriental poppies, are trickier to divide. Most garden wisdom advises not attempting to divide tap-rooted perennials, because results can be iffy. To divide these perennials, slice lengthwise through the main tap root with a knife, making sure you get a portion of the tap root along with a growing point or eye. Do not unearth the mother plant completely or you risk losing it. Give newly planted divisions from tap-rooted perennials lots of care to help them survive the transition.

Peony Flower

Peonies and dahias form tuberous or fleshy roots. When you unearth these perennials, you’ll see finger-like or even bulbous roots with clearly visible growing points or eyes. These eyes are similar to the eyes you see on a potato that’s starting to sprout. Each eye eventually forms an individual plant. When making divisions, slice through roots with a sharp knife. Place cuts so each division has at least three eyes—more is better.

Woody Shrubs that Layer

Perennials like Russian sage, lavender, candytuft, southernwood and a few other artemisias are actually woody shrubs. Don’t try to divide these plants. Instead, look around the plant for stems that might have layered. Layering occurs when branches that touch soil develop roots. Cut the branch between the main plant and the layered seedling, dig up the seedling and treat it like a division.

Trim Stems Before Dividing Perennials

Before digging a perennial to divide it, cut back stems to 2 to 3 inches. If you’re dividing perennials in early spring and shoots are small, you won’t need to trim stems. Don’t worry that you’ll stunt plant growth by snipping stems. A newly planted division isn’t able to support leafy growth until new roots sink into soil.

Dig the Perennial

Use a digging fork, shovel or spade to slice through roots and soil. To get as much of the existing root system as possible, start digging just outside the dripline of the plant. Cut a circle around the plant, angling your tool to reach beneath the clump. Your goal is to lever the plant out of the soil. In perennial beds where plants grow closely together, the narrow blade of a transplanting spade or trenching shovel fits neatly between plants.

Divide Clumps

Once you pry plants from soil, separate the clump into smaller sections. With some plants, you can do this easily by hand. Others may require a knife to slice through the plant crown, roots and soil. A specialized tool called a perennial divider has a short handle and an ultra-sharp heart shape blade that slices neatly through perennials. Work with unearthed perennials in the shade, if at all possible. Place perennials on a tarp or empty soil bag to catch soil that falls from the clump.

Use Forks to Pry Plants Apart

For large, established perennials, insert a pair of digging forks into the clump back-to-back and pull on the handles to pry plants apart. This technique works well on large clumps of daylilies, hostas and rudbeckias. All plants are easier to divide if you tackle the job before clumps are huge and overgrown. Some perennials, like goatsbeard, red hot poker and large ornamental grasses, develop woody roots that require a pruning saw to separate clumps for division.

Small Clump Ready to Plant

Each perennial division needs a growing point or shoot and roots. Those are the key ingredients for success. The more soil you have around roots, the better. But if all soil falls away during a particularly rough division process, don’t fret. Just get divisions into their planting spots as quickly as possible and water them in well. Discard oldest sections of perennials, and choose newer shoots to transplant.

Water Newly Planted Divisions

Add well-rotted compost to planting holes to give divisions a solid start. Tuck divisions into soil so their growing points sit at the same position as they did before division started. Take care not to bury perennial crowns or they may rot. Some perennials, like bearded iris or peony, have shallow planting depths. Water divisions after planting, and keep soil moist until you see signs of new growth. You might need to shade divisions for a few days if you’re planting in a sunny spot.

Natural Pest Control

Critters like slugs, pillbugs and earwigs are happy to feast on newly planted divisions. Sprinkle diatomaceous earth or limestone dust around plants and on leaves to keep plant-eating insects at bay. Reapply these natural controls if rain occurs or you wash them off when watering.

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