Beat the freeze so your spring- and early-summer-blooming plants can re-establish strong root systems.
AUTUMN IS THE best time to divide perennials that will bloom next spring or early summer. Dividing now will allow sufficient time to re-establish strong root systems before the flowering cycle begins again.
Divide them now, before freezing weather sets in.
Perennials need dividing because they grow outward from the center. If one of your plants dies out in the middle, produces fewer blooms or seems less vigorous, it might need dividing. Even if your plant is vigorous and healthy, you still might choose to divide it in order to control its size and start over with a smaller plant. Another reason to divide is to create starts of prized perennials to give to friends and neighbors.
Some perennials need dividing more often than others. Achillea (yarrow), Anchusa (bugloss), Campanula (bellflower), Crocosmia (montbretia), Hemerocallis (day lily), Siberian Iris, Lobelia, Monarda (bee balm) and Phlox are spring and summer perennials that generally bloom more reliably if they are divided every one to three years.
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Some perennials are almost impossible to divide and are better left undisturbed. Actaea (bugbane), Aruncus (goatsbeard), Gypsophila (baby’s breath), Eryngium (sea holly) and Platycodon (balloon flower) have woody, ropelike roots that tend to break easily, causing severe dieback when divisions are attempted.
Others, such as Aconitum (monkshood), Aquilegia (columbine), Euphorbia (spurge) and Pulsatilla (pasque flower), simply resent root disturbance and show their displeasure by going into major decline. Fortunately, these perennials rarely die out in the center or stop blooming with age. Give them room, and enjoy the fact that these perennials will thrive with little or no effort on your part.
One spring-blooming perennial that never needs dividing is herbaceous…