Living in the Shadow of Others

While walking through my father’s garden recently, I made a few discoveries. Now that most of the leaves on the trees and shrubs have fallen off and many of the perennials have dried up, it’s easy to see what’s underneath. Barely noticeable the rest of the year, ground covers live in the shadows of other plants.

I found some sweet woodruff (Galium odoratum), periwinkle (Vinca minor), spotted deadnettle (Lamium maculatum) and what I believe to be ground-ivy (Glechoma hederacea), a plant native to northeastern North Americaa plant that has escaped cultivation and is often found as a weed (thanks to the readers who helped me identify this). These small ground covers grow in the shade, allowing them to spread and occupy the empty spaces left by other perennials, shrubs and trees. I can no longer ask my father if he did it on purpose, but these plants act as a living mulch.

What Does Mulch Do?

Before we get into the subject of living mulches, let’s look at what an organic gardening mulch, such as ramial wood chips or shredded leaves, is used for. I’m not talking about decorative mulches, such as decorative stone or cedar mulch, which are more of a landscaping element since they don’t decompose or feed the soil.

Benefits of mulch :

• They prevent weeds from germinating.
• They reduce evaporation and by keeping the soil more evenly moist, they prevent drought.
• They regulate the temperature of the ground and reduce thermal shocks.
• They prevent erosion.
• They keep the soil looser.
• They enrich the soil when decomposing.
• They eliminate the need for hoeing and weeding, thus reducing the gardener’s workload.
• They increase the presence of beneficial microorganisms in the soil, as well as other beneficial animals such as earthworms and ground beetles.

A Living Mulch

A ground cover acts in many ways, just like a regular mulch. Because it takes up space in the garden, it prevents weeds from growing. Weeds will have a harder time germinating and spreading because of root competition and light.

A ground cover also keeps the soil moist by preventing the sun from reaching it, which also regulates the temperature in summer. In winter, the dead leaves of ground covers act as insulation against the cold. Rain cannot reach the soil directly because of the foliage, which reduces erosion. As these small perennials decompose, they enrich the soil, which feeds garden fauna such as bacteria and fungi, insects and worms. But the main advantage of living mulch over regular mulch is that once it’s established, you don’t have to replace it after it decomposes. I can’t think of a better mulch for the laidback gardener!

Competition

I can’t guarantee that these living mulches will not compete with other perennials or shrubs in your garden. They’re going to get their nutrients from the same place. Studies on the subject have been conducted in an agricultural context on vegetable crops. Living mulch negatively affects the yield of these crops. There are variations depending on the type of crop and the type of cover crop. More studies need to be done on the subject. Perhaps one day we will discover that certain ground covers work better with certain crops.

That being said, we are talking about an agricultural environment where the productivity of fields is calculated in pounds per acre. This is a far cry from the flower beds in our backyard. However, for the time being, without sufficient information to recommend it, I do not suggest putting perennial ground covers in your vegetable garden. This does not prevent me from strongly encouraging experimentation!

In an ornamental garden, my experience is that there is no need to worry about competition between ground covers and other plants. It may not be optimal, but the addition of a plant mulch should counterbalance the disadvantages of competition between plants. It’s a bit like a forest with its different levels of vegetation.

Vertical Stratification

In ecology, vertical stratification refers to the arrangement of vegetation in layers. The emergent trees are the tallest ones that extend beyond the canopy. Below this canopy is the understory layer, composed mostly of shrubs and herbaceous plants. The forest floor is at the ground level with its mosses, lichens, and the like. Patrick Ryan discusses this in his article Fall is Where You Find It.

Garden Makeover

Last summer I cut down some shrubs in my father’s garden. Under the branches of a huge spruce tree were growing a smokebush (Cotinus coggygria) and a willow shrub. These two trees were stuck together, branches intertwined, in a space far too small for their size, creating a claustrophobic effect in this part of the garden. Also, since the smokebush isn’t quite hardy in Quebec City, the upper branches can freeze during particularly harsh winters, leaving dead branches without leaves. I’ve been working as a garden designer for a few years now, and this was a shock to my sense of aesthetics!

How dare I criticize the Laidback Gardener’s garden? Well, my father admitted to me that over the years he had made many mistakes in the name of experimentation. So when an experiment failed, he would pull up the plant in question and try something else. And that’s what we did together!

I decided to rearrange this part of the garden, starting by removing these shrubs. I had planned to buy some new plants to put in there but, to my surprise, underneath this mess were several ground covers including sweet woodruff and spotted deadnettle. There was even some creeping jenny (Lysimachia nummularia), which normally prefers the sun, but had managed to survive here somehow. Rather than redo this section of the garden, I decided to add some stepping stones and transplant some ground cover to balance it out. Isn’t this a great example of vertical stratification?

Choice of Groundcovers

How would you like to plant living mulch in your existing garden or in new plant beds? The two most important factors in choosing plants are height and light requirements. Shorter, shade-friendly ground covers are preferred. The height depends on what is growing around it, but in general, lower plants are preferred. Don’t forget to choose plants that are adapted to your climate! Here is a non-exhaustive list of ground covers to use as living mulch.

1. European Wild Ginger (Asarum europaeum) USDA 4 to 7
2. Canadian wild ginger (Asarum canadense) USDA 4 to 6
3. Bugleweed (Ajuga reptans) USDA 3 to 10
4. Pennsylvania sedge (Carex pennsylvanica) USDA 3 to 8
5. Kenilworth ivy (Cymbalaria muralis) USDA 5 to 8
6. Barrenwort (Epimedium spp.) USDA 5 to 9
7. Gaillet odorant ou aspérule odorante (Galium odoratum) USDA 4 to 8
8. Spotted deadnettle (Lamium maculatum) USDA 3 to 8
9. Greater Wood Rush (Luzula sylvatica) USDA 4 to 9
10. Japanese pachysandra (Pachysandra terminalis) USDA  5 to 9
11. Partridge berry (Mitchella repens) USDA 3 to 8
12. Periwinkle (Vinca minor) USDA 4 to 8
13. Wild blue phlox (Phlox divaricata) USDA  3 to 8
14. Oak fern (Gymnocarpium dryopteris) USDA 3 to 8
15. Lungwort (Pulmonaria spp.) USDA 3 to 8
16. Creeping dogwood (Cornus canadensis) USDA 2 to 6
17. American wintergree (Gaultheria procumbens) USDA 3 to 8
18. Foamflower (Tiarella spp.) USDA 4 to 9

If you have any other suggestions, feel free to share them in the comments section!

And if you find little creeping weeds in your garden, like the ground-ivy I discovered at my father’s house, remember what the Laidback Gardener one said, “The worst weeds make the best ground covers.”