Growing Together: Autumn in the perennial garden

Don Kinzler
Forum News Service

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.

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.

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 1980s.
  • 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.
Fielding questions

Question: We have a county ditch across the road from our house and the creature in the photo has shown up over the summer. From our house it looks like Bigfoot. Could you possibly tell us what it is? I did walk over to it today and it’s covered with prickly seed pods with brownish black seeds inside. — Kent & Deb Roesler, Leonard, N.D.

Answer: The creature is wild cucumber vine, although I’ll admit the mass does resemble Bigfoot. Wild cucumber is a distant relative of our garden cucumber, and it’s an annual vine that grows each spring from seeds that were previously shed from the rounded, spiny pods. It’s extremely vigorous, easily climbing 30 feet in one growing season.

Being an annual, it’s killed by frost, which is apparently what’s happened to this dried vine. The roots do not survive winter, but it seeds itself readily, as the round pods explode and eject seeds. Once established, it usually continues to emerge each year. Wild cucumber vines are frequently seen on riverbanks, along areas of native trees and throughout lakes country. The vigorous vines can completely cover shrubs, trees and anything else on which it finds support.

What’s underneath the dried vines? Did the wild cucumber overtake Bigfoot? Out of curiosity, if you venture to take a peek, let us know what the vines are climbing over.

Q: I’m wondering if it’s advisable to apply weed-and-feed to the lawn at this time. — Lowell D.

A: Fertilizing in October is a great idea, but weed-and-feed isn’t very effective this time of year. The herbicide granules need to cling to the leaves of actively growing weeds for effective kill, and they have no appreciable properties for preventing future weeds.

Although September is a prime time to control weeds, by mid-October most weeds are soon dormant, and the highly effective fall window of application is past.

Weed-and feed products tend to be expensive, compared to fertilizer alone. A better option in October is to apply plain lawn fertilizer. It’s more economical, and the herbicide granules don’t have much, if any, effect now. Since we’re getting a little late for weed control, spring will be our next window to address weeds.

Q: I would like to save the tubers of sweet potato vine over winter to start new plants next spring. Do I keep them in a cool fridge and then plant in potting soil in spring? I did that a long time ago by just laying the tubers on the soil and they sprout. Am I correct with that method? — Lois B.

A: Ornamental sweet potato vine has become a favorite vining staple in outdoor pots and planters. In several forms, including lime green and deep purple, it’s a great accent in combination with flowering plants. It’s the same species as the edible sweet potato, and the tubers formed by the ornamental vine are edible, even if not very palatable.

I’ve never tried saving the tubers to start new plants, although I know it’s successful. Usually we take cuttings of the plant, which root readily, and keep several plants growing in a sunny winter window. You’ve inspired me to also try the tuber method.

From the sites I’ve studied about overwintering the tubers, many suggest storing around 50 degrees in a cool, dark spot, if available. The refrigerator could be a little chilly for these warm-season tubers, but it might be better than a spot that’s too warm. Some sites suggest storing them in a brown paper bag or in dry peat moss.

In late March or early April, lay the tuber horizontally in a shallow bed of moistened peat or high-peat potting mix in a warm, sunny window, and observe where roots and shoots form. The tuber can then be cut into chunks and potted, with each piece having roots and a shoot.

Keeping bare soil covered with mulch has been shown to benefit soil and plant health.
Autumn foliage in the perennial flower bed can be attractive.
Peonies, which often have diseased foliage, benefit from fall cutback.
A reader wonders what caused this mass that is covered with prickly seed pods.