DIVIDING PERENNIALS

I always enjoy growing my own plants, but there’s something even more exciting and gratifying about propagating them - producing plants by dividing, grafting, or rooting cuttings from existent stems. 

Besides being a way to multiply your plants, dividing - or splitting plants through the root into smaller sections - is often the best way to rejuvenate a mature perennial. Whether in containers or in the ground, many plants need to be divided and transplanted periodically in fresh soil and with room to spread, thereby returning them to vigorous growth and healthy blooming. This form of propagation offers instant gratification: in a matter of minutes, one plant becomes two or even more, depending on the size of the original. 

Here’s a potted walking iris that I recently divided. You can follow the steps at the end of this article if you are dividing in-ground plants.

DIVIDING IN-GROUND PLANTS

A general rule of thumb is that all clump forming herbaceous perennials can be divided, though knowing the kind of root system they have can help you determine how and when to divide the plants. 

Some popular examples of each are: 

• Spreading root systems: beebalm (monarda), aster, purple coneflower (echinacea), and tick weed (coreopsis) 
• Climbing root systems: astilbe, hosta, daylily, and many grasses
• Rhizomes: iris (shown above) bugleweed, canna lily, and some ferns
• Tuberous roots: dahlias, daffodils (and other true bulbs), and gladioli (and other corms)

You can also divide shrubs such as spirea and Siberian dogwood that sucker, sending new shoots up from the ground around their periphery.

If you're unsure, ask someone at a trusted nursery or call your nearest cooperative extension for guidance.

WHEN TO DIVIDE 

No matter why you're dividing, when you do it is critical and depends on the plant. In general, divide plants when they are dormant. 

For hardy perennials, grasses, and shrubs, this means early spring or in the fall. Perennials with fleshy roots such as Peonies, Oriental poppy, and Siberian Iris are best divided in the fall; cut back their foliage to better see what you are doing.

In northern climates, spring division gives plants several months to reestablish themselves before facing the stress of winter. If you are dividing in the fall, be sure to do so four to six weeks before the ground freezes.

In the South, where winters are mild and summer heat and drought are the greater threat, fall division is safer.

HOW TO DIVIDE 

For best results, choose an overcast day to divide plants to shield them from direct sunlight. Avoid dividing on rainy days, when you risk compacting the soil. Scheduling division for when showers are forecasted in the coming days will help transplants settle into their new environment. 

If the soil around the plant is dry, water it thoroughly the day before dividing, giving it 24 hours to absorb the moisture. 

Using a spade or shovel, dig a circle outside the plant's drip line (the widest part of the foliage), then remove the soil with a shovel until you see the roots. Slide the shovel or a garden fork under the roots and gently lift the plant out of the ground; shake to remove any loose dirt around the roots. 

Each division should have healthy roots and three to five shoots. Some plants can be gently teased apart with your hands; otherwise, cut the parent plant through the roots with a sharp hori-hori knife or other sturdy blade using a single, smooth motion. 

Plant the divisions as soon as they're made. If you must wait, wrap them in damp newspaper and keep in a shady, dry spot for no longer than one or two days.

When transplanting the divisions, start with nutrient-rich soil such as Miracle-Gro Organic™ Raised Bed & Garden Soil; dig a hole that's three times the size of the root ball and about as deep. Place the division in the hole so the top of the root ball is even with the surface, then backfill with soil. Gently tamp down around the plant to ensure the soil and root ball are in contact.

Water the plants thoroughly immediately after planting and continue to water regularly to keep the soil damp but not soaking wet.