Divide and Conquer

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In most of North America, the best season in the garden is the fall. This time of year doesn’t have the same sense of urgency and rush of spring and early summer, when cleanup and planting take priority. Garden chores that require hard physical labor are easier now that the intense heat of summer is gone. Weeds are easier to control–if you’ve kept up with them–and deadheading is no longer necessary. The time for dividing, transplanting, and enjoying the fine autumn weather has arrived.

The air is cool but the soil is still warm until November or even December in moderate climates. New plants have time to make themselves at home by spreading their roots deeply into the soil. In the fall, plants concentrate their energy on root growth rather than putting out flowers and seeds. Cool nights discourage rampant growth that could be damaged by winter freezes. New plants get a jump on their first summer, performing like two-year-olds the following year. Roots are established and they are ready to put on top growth and blooms. They are older and stronger.

In many regions, such as Zones 7 and 8, fall brings more reliable rainfall than summer. Temperatures are cooler and soils don’t dry out as quickly, so new plantings are less stressed. Pest populations decline in the fall. Nurseries are less rushed this time of year, and experts have more time to respond to questions and give their advice on fall planting and dividing in your area.

Planning time again

By now, overcrowding in the garden is painfully evident. This is a good time to move the delicate seedling that has grown into a six-foot monster hiding its neighbors in the borders. The pretty mound hidden in the back or middle of the garden can be transplanted to a more desirable location. Bare spots can be filled. A favorite herb can be moved closer to the kitchen or spread around the yard to be enjoyed more fully. Coveted plants in friends’ gardens can be traded for those in abundance in yours. Plants such as artemisias and mints that have grown too vigorously and threaten to take over your beds can be tamed or moved to the far corners of the yard. Take time to re-evaluate your garden and make improvements in design and layout. Fall planting anticipates spring.

When and where to divide

A general rule is that gardeners in Zones 5 and warmer can divide and transplant perennials and woody plants in the fall. However, experts around the country don’t always agree with that generalization. Hardiness zones are determined by average annual frost-free days and minimum winter temperatures. Examine fall and winter weather patterns in your area before you decide to divide and transplant. Great resources for this information include your local nursery, neighboring gardeners, and the Cooperative Extension Office in your area.

Robert Cary, a gardener at Sunnyboy Gardens in Earlysville, Virginia (Zone 7), says fall is an excellent time to divide and transplant herbs and perennials in the south. Any plants that are dividable can be transplanted now. He likes to be done transplanting by the first of October so the roots can settle in before leaves fall and smother them. He also notes that if plants are moved too late, they have a greater chance of being damaged by ground heaving, which exposes roots and makes the plants more susceptible to winterkill.

Gardeners at Greenfield Herb Gardens in Shipshewana, Indiana (Zone 5), never move plants in the fall. They prefer to let them die back, allowing the old growth to protect the crowns from winter cold. All of their dividing is done in the spring. Jill Miller, a horticulturist in Middlebury, Vermont (Zone 4), doesn’t like fall dividing because snow cover is unreliable. A constant blanket of snow insulates and protects plants from winter wind and freezing temperatures; bare ground in cold climates can doom fall transplants. Miller makes exceptions only if friends beg for a division of a plant that they covet. She lets them take the risk if they can’t wait until spring. Few of the gardeners I spoke to here in Wyoming (Zone 4) plant in the fall, although I’ve had success. Our winters tend to be dry and cold with erratic snow cover. Fall can linger into November or come to a sudden end in October.

Fall is the ideal time for planting in the Pacific Northwest (Zone 8). Plants can be divided and moved in October and often through December and even into January (depending on the area). Soils remain warm and conducive to root growth. Rains are reliable.

Plant division

Division is a quick and reliable way to propagate plants, especially those that don’t come true from seed. Dividing–separating a plant into several smaller plants–works well for ground covers, clump-forming perennials, bulbs, and tubers. The best time to divide spring- and summer-blooming herbs is in the fall. Fall-blooming plants should be divided in the spring. Fall is not a good time to divide and transplant members of the Compositae, or daisy family, such as coreopsis. In northern regions, perennials that are a bit on the tender side, such as English lavender, should be transplanted in the spring. For specific instructions on dividing, see page 27.

Don’t give up on gardening simply because fall has arrived. Frosts that leave your garden looking dead do not end the season; they only put an end to tender annuals. Cooler temperatures make the work easier, and planting done now frees up your time during the spring planting frenzy. Talk to experts in your area. Experiment with dividing and transplanting herbs that have outgrown their space this summer. You will be rewarded with a better garden next summer.

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