In most areas, early spring and early fall are ideal planting times for perennials. The best fall-planting conditions are a long, warm fall followed by a hard, freezing winter. But if your area tends to see a lot of freezing and thawing in winter, spring planting’s a much better bet for you—and your plants!
Can’t remember what to divide when? Try this simple rule of thumb: Divide spring-blooming plants in fall, and fall-blooming plants in spring. Of course, there are a few exceptions, like Oriental poppies and bearded irises, which are best off when divided in mid- to late-summer.
Clumps of perennials that start looking like doughnuts are prime candidates for division. The doughnut syndrome—where a ring of healthy growth surrounds a dead-looking center—starts because the center is filled with old, sickly, or woody growth. Fortunately, there’s an easy fix! Dig up the entire clump, and toss out any old growth from the middle. Cut the healthy growth into chunks, and replant.