No-Bare-Soil Landscaping

No-Bare-Soil Landscaping

No-Bare-Soil Landscaping

By Linda Dietrick, Master Gardener

At one time, gardeners could be fairly evenly divided into those who preferred to leave space and bare soil around their plants and those who preferred to see no bare soil. Older gardening friends will tell you it was simply a matter of taste. Now, however, it is widely agreed that fully covering the soil has many important benefits. Landscaping fashion has followed this good horticultural practice by favouring densely woven “plant communities” and, especially in new gardens, layers of organic mulch.

Although I’ve always been a no-bare-soil gardener, I’ll admit the choice was initially made for me. Somehow, I had to squeeze an expanding plant collection into a tiny garden, so I started ignoring the spacing requirement on the tags! Also, tired of dealing with the annual snowstorm of Siberian elm seeds that all seemed to germinate, I found that having ground covers between the larger plants meant a lot less weeding. And so I got to know a large number of low-growing perennial species that could be combined attractively with the anchor shrubs and the taller flowering showstoppers. Eventually, I learned why this was good for my plants and soil as well as very on-trend in terms of design.

First, the horticultural benefits: as the regenerative agriculture folks like to say, we need to “armour” the soil, that is, avoid tilling and keep live plants or at least their residues in place at all times. The advantages are huge: this minimizes wind and water erosion; retains moisture; keeps the soil cool; reduces compaction; suppresses weeds; sequesters carbon; helps enrich the soil; and above all protects the soil food web. As scientists have learned, plants depend on a teeming web of fungi and other (micro)organisms in the soil to supply them with critical nutrients. We should probably now think of this invisible, living underworld as part of our gardens. For details, see Darlene Belton’s article “What your garden isn’t telling you (but you can learn)” in the June 2021 MMGA Newsletter.

As for the trendiness of covering the soil, the New Perennialist movement in landscape design, most famously represented by Piet Oudolf, has learned to copy nature, where you almost never see bare soil. In natural ecosystems like the tallgrass prairie, a diversity of plants forms a dense, interlocking community of species that partly compete and partly cooperate, resulting in a stable whole that is greater than its parts. Mature natural landscapes feel beautiful and harmonious, and they seem to bring us back to our roots. New Perennialists try to duplicate that experience of nature by design. Key to their designs is the “matrix”: a ground cover layer that knits everything together like the grasses of the prairies or the understory plants of woodlands.

Today’s landscape design trends mesh well with the increasing desire of gardeners to support wildlife, especially pollinators like bees, moths, and butterflies, and the birds that depend on their larvae to feed their chicks. The climate and diversity crises make this especially urgent. As Douglas Tallamy has argued, we need to incorporate as many regionally native plants as we can into our gardens, because these are the food and habitat resources that regionally native creatures have co-evolved with and depend on. Native shrubs, perennials, and matrix plants (ground covers) are now much easier to source, thanks to local nurseries. We do well to replace non-native plants of low value to wildlife with garden-worthy native plants, or at least to add native wildflowers and grasses to our existing plantings.

In addition, we should be mindful of the invasive or potentially invasive characteristics of some exotic, i.e., non-native, plants that are still being sold or traded among gardeners or may already be growing in our gardens. For a list of “What Not to Plant in Manitoba,” visit https://mgmanitoba.com/resources/invasive-plants-weeds. The fewer of these we have on our properties, the less likely they are to invade our precious remaining natural spaces.

So how do you redesign garden beds to ensure that there is no bare soil, and that wildlife and soil health are supported? A good place to start is by adding ground covers, preferably native or at least non-invasive exotics. Below are some recommendations, grouped according to light requirements, native vs. non-native origins, and spreading behaviour.

For the reasons mentioned, native plants are preferable. In my experience, however, many of the non-native ground covers have flowers that provide nectar and pollen to non-specialist pollinators like bumble bees and hoverflies. And speaking of pollinators: to support ground-nesting bees, gardeners should consider leaving a small area that does have bare soil.

A few notes on spreading: some regionally native plants are vigorous spreaders (we do not call them invasive because they come from here), but that characteristic can be useful. For example, Canada anemone has been shown to outcompete invasive exotic grasses and keep them in check. See Robert G. Mears’s photos at https://grasslandmatters.info/native-plants-which-displace-other-plants/using-ground-cover-plants-to-lead-the-way. In his garden, Derek Yarnell, Master Gardener, has planted Canada anemone next to a mass of bishop’s goutweed, and the anemone seems to be winning.

On the other hand, many native and non-native ground covers are moderate spreaders. Generally speaking, moderate spreaders will not “take over” or outcompete your existing perennials but will grow around them or up to them and then coexist. You can keep an eye out and remove some if you feel there is too much or let the balance in the bed naturally evolve. Finally, non-native ground covers that are vigorous spreaders are not listed here because they either are already invasive or have the potential to become so with climate change.

Ground Covers (most 30 cm and under)

For sun: natives that clump or spread moderately
Pussytoes (Antennaria parvifolia)
Blue grama grass (Bouteloua gracilis)
Sheep fescue (Festuca ovina)
Northern bedstraw (Galium boreale)
Three-flowered avens (Geum triflorum)
Alumroot (Heuchera richardsonii)
June grass (Koeleria macrantha)

For sun: natives that spread vigorously
Canada anemone (Anemone canadensis)
Silverweed (Argentina anserina syn. Potentilla anserina)
Wild strawberry (Fragaria virginiana)
Wild mint (Mentha arvensis)

For sun: non-natives that spread moderately
Bugleweed (Ajuga reptans)
Snow-in-summer (Cerastium tomentosum)
Maiden pinks (Dianthus deltoides)
Stonecrops (shorter ones) (Sedum species)
Thyme (Thymus species)
Prostrate speedwell (Veronica cvs. such as ‘Tidal Pool’)
Creeping phlox (Phlox subulate)

For shade/part shade: natives that clump or spread moderately
Wild ginger (Asarum canadense)
Oak sedge (Carex pensylvanica)
Sweet scented bedstraw (Galium triflorum)
Oak fern (Gymnocarpium dryopteris)
Star-flowered Solomon’s seal (Maianthemum stellatum syn. Smilacina stellata)
Purple oat grass (Schizachne purpurascens)
Downy yellow violet (Viola pubescens)

For shade/part shade: natives that spread vigorously
Virginia creeper (Parthenocissus quinquefolia)
Western Canada violet (Viola canadensis)

For shade/part shade: non-natives that clump or spread moderately
Dwarf Chinese astilbe (Astilbe chinensis ‘Pumila’)
Bergenia (Bergenia cordifolia)
Red barrenwort (Epimedium x rubrum)
Cranesbill (Geranium macrorrhizum and others)
Deadnettle (Lamium maculatum)
Fleeceflower (Persicaria affinis ‘Dimity’)
Lungwort (Pulmonaria species)
Barren strawberry (Waldsteinia ternate)

Until ground covers fill in or new plants are established, the soil can also be covered with a thick layer of organic mulch such as arborist’s chips. Landscape fabric and rock mulch should not be used, as they are detrimental to plant and soil health.

FEATURED PHOTO (courtesy of L.Dietrick):
Image of “goldenlocks” elder underplanted with wild ginger, alumroot, and fleeceflower