Every spring, nurseries and garden centers buzz with gardeners looking for that perfect mulch to spread in their yards. Gardeners want mulch with beneficial properties and curb appeal. Bag after bag is loaded into pickups, trunks and even backseats.
But did you know there also are living mulches? I’m talking about the soil-huggers, the low-growers of the plant world—the unheralded herbal groundcovers. Low-maintenance herbal groundcovers are mulches that eliminate weeding, prevent soil erosion, insulate in winter and retain water in summer. In this case, beauty, delightful fragrance and edible landscaping are just icing on the gardening cake. Nothing brings mulching benefits as nicely as agreeable herbs.
Herbs are masters at adapting to a variety of soils and reproduce all by themselves. As living mulches, they’re rivaled by none. There isn’t one good reason to consider herbs as groundcovers—there are five great ones.
1. Wise Watering
Living groundcovers can conserve water in your garden, which can save you money wherever you live. If you live in a drought-stricken area like California, it can be especially important. Under-planting with herbal groundcovers holds moisture in the soil by slowing water evaporation and allowing the water to remain available to the plant roots below. The groundcovers also protect the soil from drying in the sun’s rays. Most groundcovers do well without any supplemental watering.
Mediterranean herbs do well with less water. Some herbs need more than others, but generally they hold moisture in the soil, allowing for less-frequent watering than most plants. Whether your groundcovers need supplemental water will certainly depend upon your climate. If needed, most herbal groundcovers do well with once-a-week deep watering (instead of light watering a few times a week).
Do a little homework to be sure that you’re planting herbs that have close to the same water requirements, so that the water trapped in the soil can benefit all your herbs equally. It would be a shame to over-water a Mediterranean herb simply because it was close to a more water-hungry plant. Alternately, you can choose one type of herbal groundcover for one garden area and a different type for another.
2. Incorporate Insulation
As handy as herbal groundcovers are in the summer as water retainers, they’re equally impressive as insulators in the winter. The roots of the living mulch grow together, forming a blanket of protection that shields roots and bulbs from fluctuating air temperatures. Personally, when I drop my hundred bucks in the spring on exciting new plant finds, I’d like for them to last more than one season. My hardy under-plantings have been like small green superheroes, sans the capes.
There’s no need to worry about herbal groundcovers inhibiting bulb or perennial growth. Most bulbs have no trouble growing right through the groundcover in the spring.
3. Eliminate Erosion
We gardeners strive to give our precious gardens healthy, nutrient-rich soil by using organic gardening practices, minimal tilling and composting. Don’t forget to consider soil erosion, too. Rain, wind and sun all contribute to soil runoff (or erosion). Not only is fluffy soil sloshed away, but plant roots are left exposed and vulnerable to the elements.
How do you know if erosion is a problem for your soil? Consider the rainfall, wind activity and heat intensity of your region. When we think of erosion, water is usually the first thing we point a finger at, and it certainly is one of the biggest culprits. I don’t mean the life-sustaining shower of the watering can, but rather, big water. If your area sees a lot of rain, and especially if you have any slope to your property, water is the biggest soil pirate around.
Another example is wind. If you live in an area that endures strong wind activity, the winds don’t have to be overly intense to literally pick up the soil and redistribute it everywhere but where you’d like it to be. In the Midwest, for example, the subsoils may freeze, but the topsoil remains easy pickings for the wind to blow right out of your garden.
Between their fibrous root system and their leaves, groundcovers help bind the soil and prevent erosion. Ideally, gardeners should strive to have every bare piece of soil in their yard and garden covered. Herbal groundcovers like periwinkle (Vinca major or V. minor) and bugleweed (Ajuga reptans) make excellent soil binders. Living mulches also improve soil structure because they provide a healthy habitat for soil organisms.
4. Win the Weed War
Groundcovers are state-of-the-art weed control. This is welcome news for my knees and back, as I am no longer a young gardener. The first way groundcovers prevent weeds is by simply not sharing food with them. As the groundcovers creep along and reach out to each other, the weeds have to compete with the herbs for water and nutrients. Usually, the weeds are no match for them. Groundcovers block the sun, and the weed seeds simply can’t germinate without the light source. Herbs have been known to outright smother weeds, as well. I haven’t worked with a more effective barrier.
Every once in a while, a slender weed escapee pokes up in the middle of my groundcover. For a minute, I feel a bit sorry for the lonely little guy. But not that sorry. He slides out of the soil easily and I’m done weeding for months.
5. Botanical Bounty
Herbal groundcovers not only add extra beauty to a garden or yard, but they also add the texture that makes our gardens interesting and original. Of the many reasons I grow herbs in my beds, the first is that they invite all the senses out to play, from how they feel to the touch to their individual colors and surprising scents.
Fair warning: Some herbs’ bounty can become overwhelming.Choose groundcovers that fit your garden. Some herbs may fit the bill as groundcovers, but also are invasive to the point of taking over your garden. Herbs like sweet woodruff (Galium odoratum) really take control of a situation to the point of extremes. With sweet woodruff it isn’t all bad news, however. It would be perfect if you have a specific area that really needs a living mulch and you don’t have other soft-wooded plants you’re interested in growing there—maybe in a tree grove, perhaps. Or if you have a vacant area that you need covered in a hurry, planting sweet woodruff could be appropriate.
Another invasive herb is the mint species: Peppermint (Mentha ×piperita) and spearmint (M. spicata) are quite aggressive. These plants make your house a home—forever. In fact, they’re so invasive that I grow them strictly in pots. Creeping pennyroyal (M. pulegium), also a mint, has gotten some attention as of late. Although it makes a terrific ant repellant, it’s a huge invader and can be toxic if ingested. It’s considered potentially hazardous to people and pets; err on the safe side and leave it out.
The fact that reliable herbs make accommodating groundcovers is not surprising. Gardeners have long sung the praises of the exhaustive attributes of herbs. Groundcovers are just another virtue of the most versatile plants in the world.
Chris McLaughlin’s book on composting, The Complete Idiot’s Guide to Composting (Alpha/Penguin, 2010), will be published in April.