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It's time to enjoy — and complete the updated tasks of — autumn in the perennial garden

In today's "Growing Together" column, Don Kinzler explains how to incorporate newer research into your fall flower beds.

Keeping bare soil covered with mulch has been shown to benefit soil and plant health. David Samson / The Forum

It might seem like gardening and its methods are timeless. If so, we could continue doing our yard and garden tasks the same way we’ve always done them.

Gardening recommendations evolve, though, as we discover better ways, adding new findings to everyday practicality.

There are notable examples of how our gardening methods have evolved. Putting pebbles inside the bottom of flowerpots was once the norm, until science showed this layer of change actually impedes the drainage that pebbles were meant to provide, so we’re better leaving them out.

Raking leaves was a fall tradition until we learned a healthier lawn is created by mulching them back into the turf .


Peonies, which often have diseased foliage, benefit from fall cutback. David Samson / The Forum

Perennial flower gardening has also changed over the years, most noticeably in autumn. As a young boy, I helped my mother with the fall cleanup of flower beds, and, like many others, we clear-cut all plants and raked out all leaf accumulation so everything looked clean and tidy.

The flower beds always grew beautifully, but in the meantime, we’ve found better methods that can keep the flower beds and their soil sustainable for future decades.

Autumn foliage in the perennial flower bed can be attractive. David Samson / The Forum

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Here are some ways that newer research can be incorporated into a healthier perennial flower bed.

  • Autumn holds a special beauty in a perennial flower bed that goes deeper than fall-flowering mums and asters. There’s newfound appreciation of the golden-brown hue of leaves changing color while flower heads fade to shades of rich brown. There’s quiet scenery to enjoy in autumn perennials, if we pause the urge to hurry fall cleanup.
  • Perennials love organic material incorporated into the soil, and fall is a great time to add compost, peat moss, leaves or bagged manure. Organics provide a rich, lively soil environment and provide the best remedy for both heavy clay and too-light sandy soil. Incorporate several handfuls of material into the soil around existing plants each fall.
  • In nature, soil is rarely left exposed, unless it’s a barren desert. It’s healthier for soil to be covered, which creates a soil alive with microbes. Mulching the soil around perennial plants not only conserves moisture, but allows the soil to improve and build.
  • Organic mulches are more plant-friendly than rock mulch. Rock mulch was the landscaping norm for decades, and is still used extensively in commercial and many residential landscapes. I’ve landscaped extensively with rock mulch in the past, and plants have done fine, but if you’ve ever lifted a five-gallon bucket of rocks, you know it’s heavy. Over time, the weight of rock compacts the soil it’s covering, although breathable landscape fabrics are vast improvements over the impermeable plastic mulch that was the standard in the 1970s and ‘80s.
  • Organic mulches like shredded bark, wood chips, pine needles and cocoa hulls are more like nature’s own soil covering around perennials. Such mulches don’t become hot like rock mulch, and their weight isn’t burdensome to the soil. Apply a 5-inch layer for best weed control, and replenish when it settles.
  • Should weed control fabric be used under the mulch in a perennial garden? You certainly can if you wish, but the favored trend is to place the organic mulch directly on the soil with no fabric installed. The mulch layer in contact with the soil will slowly decompose into a rich, root-friendly compost, impossible if fabric is covering the soil. Weed control is still accomplished if the mulch layer is thick enough.
  • Instead of clear-cutting perennials in fall, the above-ground parts of most perennials, referred to as tops, are best left intact over winter, and removed in spring before new growth begins. They have a subtle winter beauty when viewed against a snowy backdrop, and the tops help catch insulating snow, for better winter survival.
  • A newly promoted reason for leaving perennials intact is to protect native bee pollinators that build wintering nests in the hollow stems of perennials. Providing such winter habitat for pollinators can better assure that our apple trees, cucumbers, squash and other insect-pollinated plants will yield fruit next summer.
  • Some perennial tops are better removed this fall. Daylily, iris and hosta become flat and limp by next spring, and cutting back to an inch or two above ground level in autumn is preferred. Any perennials whose foliage is highly susceptible to disease, such as peonies, are best cut back to an inch above soil, with the tops discarded off-site.

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at or call 701-241-5707.


Don Kinzler
Don Kinzler, Growing Together and Fielding Questions columnist. The Forum

Don Kinzler
Don Kinzler, Growing Together and Fielding Questions columnist. The Forum

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