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Great Gardening by Sally Cunningham: Spreading the word on groundcovers

The topic of “Groundcovers” sounds mighty dull. Experienced gardeners and landscapers might even skip it, when it appears in a lecture or article. With the help of FLCC (Finger Lakes Community College) instructor Rochelle Smith I hope to provide some surprises and create some enthusiasm for these hardworking little plants – including many that aren’t so little at all.

Rochelle taught the groundcovers class at Plant WNY’s Education Day last week, a February event that is attended by landscape professionals as well as master gardener volunteers and other serious gardeners. She is a dynamic teacher who could bring any topic to life even at 4 p.m. after a full day of classes, which makes her Finger Lakes students fortunate. Similarly, the NCCC (Niagara County Community College) horticulture students – many attending the training days – are clearly thriving under the leadership of educator Carolyn Stanko. In both schools these “kids” of many ages are learning science-based landscaping and plant-production skills, and the industry is gaining educated employees.

Surprising groundcovers
The first surprise may be what we mean by “groundcovers,” and what I’m betting most people think they are. Put to the test, most folks – is this you? – could name Pachysandra, Myrtle and possibly Ajuga or ginger. Savvy homeowners might ask in the garden center for spreading sedums or creeping thyme for sunny locations, and may know to ask for lamiums or sweet woodruff (Galium) for shadier spots. What these plants all have in common is that they are short, as in 4 or 5 inches.

Surprise: Groundcovers do not have to be short. It all depends on what ground you want to cover.

About 11 years ago Cornell University distributed an information sheet (still in many garden center and Extension offices files), that accompanied a study of “Perennial Groundcovers that Block Weeds.” Along with several sites across our state, Lockwood’s Greenhouses in Hamburg agreed to the trial. They planted perennials on a 5-by-30-foot sloping bed, to see which ones survived and blocked weeds with minimal human assistance during just the first year. The bed still thrives, with only occasional staff attention. In this case the best weed-blocking perennials proved to be Ladies mantle (Alchemilla mollis), Butterfly weed (Asclepias tuberosa), Catmint (Nepeta), Germander, and the Sedum cultivar ‘John Creech.’ Unexpectedly, Coral bells (Heuchera) did rather well too. This performance was in full sun in a driveway-baked bed.

If you want to cover a bank or a large area in your yard with an undulating, textured planting of one species, or perhaps two or three huge swaths, then those plants might be for you. Other 8- to 24-inch perennials that also spread well include the following. (Always match plants to the site.)

Brunnera macrophylla (such as ‘Jack Frost’)
Campanulas (many species and cultivars of many heights)
Dianthus (always nice texture, colorful flowers for limited periods)
Epimediums (not used nearly enough; truly delightful)
Hemerocallis (Daylilies of many color, heights and bloom times – and I do not mean “Ditch lilies”; you can do better than that.)
Helleborus (long-lasting shade lover with every better cultivars)
Hostas (the royalty of all spreading, weed-blocking, tree-root tolerant plants)
Phlox subulata (a sea of color in spring)
Stachys byzantina (Lambs’ ears, for silver, fuzzy texture)
Tradescantia virginiana (Spider wort)
Some woody plants, vines, and grasses also serve as groundcovers in the right places.

How fast?
There is one way you’d rather not be surprised, and that is by choosing a groundcover that is so good at its job that it takes over your garden or the entire yard. Between 50 and a 100 years ago many gardeners planted a pretty “groundcover” with a fluffy white flower all around Western New York houses. From Buffalo to East Aurora, the gardeners still moan, “What is this? I can’t get rid of it no matter what I do!” It’s Aegopodium, called Goutweed or Bishop’s weed. It is simply a dreadful thug, requiring lengthy and repeated chemical, physical or light-blocking methods.

I strongly recommend you also avoid the beautiful Houttuynia cordata (Chameleon plant), unless it’s contained between two cement structures (and even then I believe it leaps in the night). Others to avoid are Tovara ‘Painter’s Palette’, buttercup species, and mints, unless you have lots of time and love to fight for control.
Here is the groundcover challenge: You want a plant that covers the ground, preferably quickly enough that the weeds can’t jump in, but you don’t want it to run rampant. Rochelle reminded the class of the adage that describes most perennial plant behavior: “The first year it sleeps. The second year it creeps. The third year it leaps.”

So your groundcover probably won’t block every weed seedling in year one. Plan to hoe or pull weeds between the new plants. Or plant seeds or annual plants between them. Depending on the height of your chosen ground coverers, try short cosmos or love-in-a-mist or alyssum. Then be patient.
And while you’re patient, don’t assume that your spouse or yard helper knows what’s going on there. Many a marriage had a rocky weekend when the NGS (non-gardening spouse) mowed over the recently planted, scraggly-looking patch of Liriope or daylilies. Rope it off, make a clear edge, or take Rochelle’s advice to put out signs saying “NOT A WEED.” That’s all they need to know. It’s a Notaweed.

Aesthetics count
Typical reasons to use groundcovers are weed blocking, decreasing lawn and lawn care, providing flowers for pollinators, and forming islands around treed areas. But don’t forget the aesthetics. Landscape designs are greatly enhanced when groundcovers are chosen to complement specimen shrubs or perennials. Give a shrub a skirt. Creeping thyme or other “Steppables” outline pavers prettily (and smell great). A perennial bed acquires definition from a distance when you define the front edge with a one-color planting such as Lambs’-ears or coral bells.

A yard without groundcovers is a dressed-up lady with no necklace or scarf. Dress her up – and she’ll help you with your weeding.

Sally Cunningham is a garden writer, lecturer and consultant.

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