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Partly cloudy skies early will give way to cloudy skies late. Low around 65F. Winds light and variable..

Partly cloudy skies early will give way to cloudy skies late. Low around 65F. Winds light and variable.

Dividing perennial plants regularly promotes better plant health, more colorful blooms, and more manageable gardens. It’s a great way to add plants to a garden or share favorite plants with friends. Mark your calendars now for an opportunity for sharing and obtaining new plants, coming up on Sept. 10 at the Scott County Master Gardener Volunteers Plant Swap. Read on for more information. 

Perennials that aren’t divided develop crowded roots, making it difficult for the plants to absorb water and nutrients. When this happens, the plants bloom less often. Signs that it’s time to divide plants include decreased flower size, less vigorous plant growth, development of a hole in the center of a planting, and/or sparse foliage at the bottom of a plant. While each perennial is different, many need to be divided every three to five years. 

Some perennials don’t like being divided. These include butterfly weed (Asclepias), euphorbias, oriental poppies, baby’s breath (Gypsophila), gas plant (Dictamnus albus), Japanese anemones, false indigo (Baptisia) and columbines (Aquilegia). Others like Lenten and Christmas roses (Helleborus) are easiest to move as small seedlings. 

The best time to move or divide many perennial plants is the fall. Fall divided plants divided have more time to develop roots before the summer’s heat than those divided in the spring. Divide plants in September when the nights begin to cool. Plants need four to six weeks of frost-free growing time to establish roots. 

Don’t divide plants on a hot, sunny day. Wait for a cloudy day, ideally with a chance of light rain in the forecast. If possible, prepare the area you will move the segments to before you divide the plants. Sometimes it’s best to cut back the foliage if the plants are very large. Cutting back foliage helps the plant retain moisture. 

Make sure the soil has dried out after rain or watering to avoid having mud compact on the roots. If it’s been dry, water the plants a day or two before dividing, allowing the soil to be damp, but not muddy. 

To avoid damaging the roots, dig outside the root zone or drip line, usually one or two inches beyond the outer edge of the foliage. Dig straight down about 4-6 inches the entire way around the plant to sever any remaining roots. Then dig at an angle deep under the roots at several points to loosen the plant. Use the shovel to lever the plant out of the hole. A large plant may need to be divided in the hole to get it out. 

Once removed, shake off loose soil and remove dead stems or leaves. Depending on the type of root, divide accordingly into three to five segments, discarding any small or damaged segments. Perennials multiply quickly; one stem will triple or quadruple each year. Simply dividing a perennial in half means it will need to be divided again soon. 

Spreading root systems have slender matted roots that appear from many locations with no distinct pattern. They are found on plants like asters, bee balm, lamb’s ear, purple cornflowers, and many other common perennials and often crowd out their centers. They can be divided by hand or with shears, however, if the roots are woody, two digging forks put back-to-back in the center of the plant can be used to separate. 

Clumping root systems originate from a central clump with multiple growing points. They often have thick fleshy roots and include astilbes, hostas, and many ornamental grasses. It’s important to keep at least one eye in each segment, more if larger plants are desired. Often a heavy sharp knife is needed to cut through the crown (area between leaves and roots); two digging forks can also be used. 

Rhizomes are stems that grow horizontally at or above the soil level. Bearded irises and canna lilies have this type of root system. Cut and discard the rhizome sections that are older. Also, inspect them for disease and insect damage. Damaged rhizomes should be trimmed and treated or discarded. 

Tuberous root systems are large and fleshy; a tuber has roots at one end and a sprout at the other. Dahlias and peonies have tuberous roots. If the tubers can’t be pulled apart, they can be cut apart with a sharp knife. Every division must have a piece of the original stem and a growth bud attached. After division they can either be replanted or stored for spring planting. Some perennials with tough root systems, like red-hot pokers, may have to be divided with a shovel, saw or ax. Vigorously hosing the soil off makes the root system easier to divide. 

Replant the new segments quickly, preventing the roots from drying out completely. If you need to hold them temporarily, move them to a cooler area (50 degrees) with higher humidity (50 percent) like a garage. Cover them with dampened newspaper to help the roots retain moisture. If they do dry out, soak the segments in a bucket of water for one hour before replanting. If you don’t have a spot for the new plants, establish a holding or nursery bed to keep the plants until you are ready to plant. 

Look at the segments and choose the healthiest to replant. Throw out segments that have discolored stems, matted roots, or eroded crowns. Makes sure the new hole is wider than the roots spread out. Place a mound of soil under the roots and spread the roots around the hole. Don’t plant other plants too closely. Spreading out the roots in the hole gives you an idea of how large the plant will be the next spring. 

Add soil and compost to the hole, making sure the segment remains at the same level as the previous planting. Compost will renew the soil and cut down on potential pests. The replanted segments will settle, and the compost will help to raise them up, improving air circulation and drainage. After replanting the segment, water it well and tamp down the soil to prevent air pockets from forming. 

If you have all the plants your landscape can hold for now, consider sharing them at our Plant Swap, September 10, 2022. Go to https://tinyurl.com/SCEXTPLANTSWAP for information on how to participate. 

Don’t forget to send your gardening questions to ‘Ask the Hort Agent’—advice from Sharon Flynt, Scott County Extension Horticulture Agent, University of Kentucky Cooperative Extension Service. Mail them to Sharon Flynt, Agent, 1130 Cincinnati Road, Georgetown, KY 40324 or send your email to sflynt@uky.edu. If your answers are used right here in ‘The Garden Spot’ column, you will receive by mail a reusable GARDEN SPOT farmers market/grocery tote as a THANK YOU! Remember, whatever your gardening interest or goals, the UK Scott County Cooperative Extension Horticulture Program is designed to provide useful, up to date, research-based information free of charge to assist all people of Scott County with your gardening or operational needs.

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