Q. Can I divide perennials in the fall?
A. Late summer or early fall, when the worst of summer’s heat is over, is a great time to divide perennials. Because there are so many gardening tasks in the spring, it also helps to spread your workload. Perennials need to be divided when they develop small or sparse foliage or bare spots in the middle. These signs are a good indicator that there is too much competition for water, nutrients and space.
Fall divisions will have plenty of time to develop new roots as long as you allow 6 to 8 weeks before the ground freezes. Iris, peonies, poppies and moss pinks even do better when divided in early fall. The only poor choice of a time to lift and divide perennials is in August, a hot month with little rain. If possible, lift and divide perennials when they are not in bud or bloom.
Choose a cool, cloudy day to divide perennials and try to water a day ahead. If dividing in the fall, cut the foliage back to 6 to 8 inches. Use a shovel to dig under all 4 sides of the plant about 3 inches out from the edge of the plant. Lift out the clump to be divided, shake off the loose soil and remove any dead leaves or stems. Clumps with fibrous roots can be pulled apart by hand or with spading forks. Plants with tough, dense, roots (like hosta or daylily) may need to be cut apart with a knife or sharp spade. Discard the old centers of the plants as well as any soft, rotted roots. Re-plant your divisions immediately, water them well, and keep them moist for several weeks.
Lists drought tolerant plants for New Hampshire.
By autumn, many of the spring- and summer-blooming perennials have faded, leaving the garden bleak and colorless. But some perennials, such as asters and goldenrod, will provide vivid color until the first killing frost or even later.
This fact sheet offers suggestions on designing a colorful border planting of annuals and perennials.
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