Rough-looking perennials? Here’s what to do.

A few of the perennials in my garden borders are starting to look a bit rough. I was wondering if I should cut them back now or wait until later this fall or even until spring? I want to do what is best for the plants.

— Jason Kim, Evanston

My goal at home is to leave as many of the perennials up as I can, so there will be winter interest in the garden. I avoid cutting back perennials in my home garden until they look bad. When a plant looks bad is subjective, depending on each gardener’s perspective and goals for their garden. Leaving the perennials up with leaf litter in the beds provides shelter for overwintering pollinators. Generally, I do not cut back any of the perennials in my garden in the fall, leaving the more natural appearance I prefer. Hostas can have good fall color but will eventually collapse and lay flat on the ground in late fall. Since they will have no winter interest, just cut them back once they collapse. Goldfinches will visit the seedheads on my coneflowers, so cutting them back or deadheading removes this food source for the birds.

Whether to cut your perennials back later this fall is more about how you like your garden to look through the winter than about the health of your plants. Some gardeners prefer a clean look with all the plants cut back and a light layer of mulch over the beds. Established perennials do not need to be mulched for the winter. If you decide to cut back the perennials in your beds and mulch, it is best to use a very light layer of mulch of an inch or less. Since I do not cut back my perennial borders in the fall, some leaves blow into the borders and provide a light layer of mulch for the beds. I prefer this more natural look for my garden. Then the perennials get cut back in spring before they begin growing. If you run late with spring cleanup, be careful as you cut back the perennials so as not to damage any new growth that may have started. Cutting back perennials to a height of 6 to 8 inches in the spring instead of at ground level will help support and encourage pollinators in your garden.

If you have installed any new perennials this year, they should be mulched for the winter to avoid frost heaving in spring. Mulch around the plants, but do not bury the crowns. The freezing and thawing of soil in the spring can push newly installed small plants like perennials grown in 1-gallon containers out of the ground. Mulching new perennials installed in fall also gives them more time to develop roots and get established before winter sets in.

For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.