Mulching garden beds has been a consistent ‘must-do’ for many gardeners. Mulching reduces moisture evaporation, suppresses weeds, adds nutrients to the soil, reduces erosion and in many cases improves moisture absorption. Wood and bark chips are the most common materials employed. Recently I have seen and read more about the negative effects of wood chip mulches. In particular when these mulches are over applied and allowed to compact, they can actually retard rain water absorption. Thickly applied mulch can retard the growth and expansion perennials. In his book The Know Maintenance Perennial Garden, Roy Diblik discusses how unnatural wood chip mulch is. In areas that get adequate rainfall to support a tight matrix of plants, a living, or green, mulch is the ideal.
For many sustainable and naturalistic gardens the goal is to create this ‘green mulch’ or ‘living mulch’ by filling the space between garden features or larger plants with more plants. ‘Green mulch’ is living plant material that performs all the functions of wood mulch such as weed suppression and soil moisture and temperature moderation. In addition properly selected green mulches offer additional benefits like supporting wildlife and insects with food and cover, lower maintenance (since they do not to be replenished or broken up on a regular basis). This green mulch may be a single species or a variety of plants that form an interlocking matrix. This matrix is most like what you would encounter in a meadow or woodland setting.
An example of a classically mulched bed. Each plant is distinctly identifiable and there are no random plants to confuse the composition. |
One means of creating a green mulch is to install plants closer together so that they quickly grow together to create a continuous green carpet of foliage. This is one of the themes of the book New Naturalism, by Kelly Norris, published in 2021. The trick here is to create plant communities that a good match to your site conditions and that the plants play well together.
Golden ragwort is excellent native ground cover. It spreads rapidly in moist, partly sunny locations. It also seems to suppress invasive weeds like Japanese stilt grass and garlic mustard. |
Using spring ephemerals for this purpose is a very natural means of creating a matrix. These perennials naturally flourish early in the year when tree and shrub canopies are open, then slowly go dormant as the canopy closes up. They return again the following spring. In the Mid-Atlantic you may find Dutchman’s breeches and squirrel corn (Dicentra sp.), mayapple (Podophyllum peltatum) and Virginia bluebells (Mertensia virginiana) as common examples of these. A limitation with using ephemerals is that they do totally disappear after setting seed. They are ideal in an established perennial or shrub bed where you just need something in early spring while the larger plants are leafing out.
Ephemerals, like cutleaf toothwort, Cardamine concatenata (in bloom), and Dutchman's breeches, Dicentra cucullaria, fill out in early spring. but disappear as the tree canopy fills in. |
Using short-lived species that survive primarily by
reseeding is another means to establishing a sustainable living mulch. By nature these are opportunistic gap
fillers. As the longer lived perennial
and shrub layers get established these reseeders tend to be squeezed out as
their preferred, open habitat disappears.
Yellow fumewort (Corydalis flavula), American pennyroyal (Hedeoma
pulegiodes), common yellow woodsorrel (Oxalis
stricta), and self-heal ( Prunella
vulgaris) are some of the shorter species that can be used in this
way. Taller, showier species that can be
used as temporary gap fillers include wild columbine (Aquilegia
canadensis), Partridge pea (Chamaecrista fasciculata), fleabanes (Erigeron annuus and E. philadelphicus), and black-eyed Susans (Rudbeckia hirta).
So if you are willing to give up the repetitive chore of mulching your garden beds, consider having your plants do that job for you and establish a living mulch.