"What to do when" is a garden game we all play. The rules are both imprecise and elusive when it comes to the essential chores of cutting back and dividing plants.

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by Valerie Easton

illustrated by Susan Jouflas

“What to do when” is a garden game we all play. The rules, however, are both imprecise and elusive when it comes to the essential chores of cutting back and dividing plants. Dealing with the biomass generated by a garden is intimidating enough, let alone trying to propel a shovel through a root ball the size and consistency of a boulder.

Luckily, we live in a forgiving climate. Long, damp autumns and cool, wet springs give us plenty of latitude in what to do when. Plants have such an abundant life force that our experimentations and mistakes don’t set them back much. Have you noticed how it’s always the plants we care least about that persist no matter how we fumble?

Be assured that plant protocols are based as much on aesthetics as on survival. Throughout the growing season it’s a good idea to cut back plants with the potential to rebloom. Clipping yarrow, astrantia, lavender and geums encourages a second flush of flower. Some plants, like poppies, fade into ghosts after they flower, so you may as well off them. If you can stand a little disorder, perennials like coneflowers, rudbeckia and globe thistles have a real presence even after death, especially on a cold morning when a glisten of hoarfrost enhances their shagginess.

Another delight of the winter garden is watching birds gather fluff off decaying grass blooms or gobble seed while teetering atop perennial skeletons. Soon enough, freezing nights and pounding rain will mash them down into black goo — at which point you probably want to find the time and fortitude to clean them up.

Other gardeners prefer looking out their windows at a tidy garden. One good gardener I know cuts everything herbaceous back to the ground in November, giving her a clean slate for winter and less work come spring. Remember that scene in “A Secret Garden” when sour little Mary is enchanted to find new growth pushing up through the debris of the forgotten garden? That annual springtime joy is a gardener’s reward for sooner or later following through with cleanup.

If you watch your plants closely through the seasons, you’ll pick up on the clues they give as to what is needed when. In springtime, when the new growth of hardy fuchsias and ferns pokes through the ground, it’s time to carefully cut away the brittle sticks of your fuchsias or the tattered old fronds from your ferns. The aged parts of the plant have protected the new growth from late frosts; now it’s time to clear them away to let sun and air nurture the emerging shoots.

Although the rule-of-thumb is to divide spring-blooming perennials in autumn and late-blooming perennials in early spring, plants tend to make it clear when they need attention. Dwindling bloom tells you that daylilies, crocosmia, phlox and others need to have their root balls dug up and split apart. Primroses, iris and ajuga appear piled up and congested even above ground. Hostas, peonies and columbines, among others, flourish for as long as a decade without being dug up and cut apart. Ornamental grasses can be tricky. It’s best to wait until March to cut them back hard, except for some of the evergreen ones like carexes, which would prefer not to be messed with at all.

I’m embarrassed to admit that when I started gardening I looked up every single plant in my “Sunset Western Garden Book” and made exhaustive notes on how to care for each. That’s how much I trusted my own instincts and powers of observation. But I don’t actually remember looking at my notes much. Having it all written down was reassuring enough. Now with the new book “Perennials: The Gardener’s Reference” by Susan Carter, Carrie Becker and Bob Lilly (Timber Press, $49.95) there’s no need for such obsessive behavior. Despite its big-hardback sturdiness, I bet this book will end up dirty and tattered from being carried around for frequent reference. Or you can take a field trip to the Bellevue Botanical Garden Perennial Border and see for yourself how the authors of the book care for a symphony of plants so skillfully that the border is gorgeous at all times of the year.

Valerie Easton is a Seattle freelance writer and author of “A Pattern Garden.” Her e-mail address is valeaston@comcast.net. Susan Jouflas is The Seattle Times’ assistant art director/features.