Getting Sedgy With Green Mulch
How many times have you been walking in a woodland or meadow and seen animals hard at work spreading wood mulch? Chickadees carefully placing a piece here, squirrels using their tails to smooth a patch over there? It’s a sight to see as nature works to reduce weed competition and add organic matter to the soil.
But you know that’s not REALLY how nature works, because in nature functional and ecological landscapes are about plants, plants, plants -- green vegetation at every level from the ground layer up through taller perennials and grasses to shrubs and trees. Nature uses green mulch – or plants – to fill open spaces. Plant layers build soil, conserve soil moisture, compete against weeds, filter water into the ground, clean the air, and provide all manner of habitat benefits for wildlife. So why do we insist on going against nature and applying wood mulch every spring in our urban landscapes? Wood mulch keeps plants in a state of establishment, preventing them from self sowing, mingling, or providing all the benefits that we hoped for when we dug them in.
Photo courtesy of Mt Cuba Center.
One of the best group of plants to act as a green mulch are sedges, which include a wide variety of species that will fit most any site condition. In my design practice I tend to place sedge 12” apart on a grid pattern after inserting sweeps and masses of various forbs and ephemerals. In 2-3 years the sedge usually fill in to become a lovely carpet of green, eliminating the need for wood mulch and severely curtailing weed pressure.
Here’s a short list of my favorite sedges, mostly because they are site adaptable and work well together, but they are really just a drop in the bucket of what’s available. There are many reasons for the growing popularity of this group of plants!
Carex albicans (white-tinged sedge)
Hands down my #1 go-to sedge. Year after year it impresses me with its resilience not only in dry shade but in moderately-moist sun and in the part shade of taller plants around it. You can almost double matrix with it having warm-season bunchgrasses planted alongside; the sedge greens up earlier in spring and, once summer hits, the bunchgrasses provide a little shade. Try mixing in Bouteloua curtipendula, Schizachyrium scoparium, or Sporobolis heterolepis if planting in a sunny site.
Carex sprengelii (sprengel’s sedge)
Perhaps my second in command. Why? Because dry shade and moist sun work fine, but especially because it pairs well with shorter, finer-leaved species like many on this list. Those pairings provide nice textural contrast, especially if the landscape will be sedge dominated with reduced forbs (think something like a deep shade meadow where leaf variability counts for more).
© Izel Plants, 2017
Carex eburnea (bristleleaf sedge) and Carex pensylvanica (Pennsylvania sedge)
It’s not fair to lump these two species together, but I’m doing so because they both stay low and spread. In the case of C. eburnea, it looks like someone buried a troll doll up to its eyes; this sedge will slowly seed around and is great among stepping stones. Penn sedge spreads by rhizome and can turn into a shade lawn or fill gaps in a sunnier planting with taller plants around it.
Carex blanda (common wood sedge)
A shade to part shade spreader, the thicker leaves look nice against the finer leaves of other species, but it can roam more than many of those finer-leaved species, too. Anticipating its spread may mean you initially plant it in scattered masses or single specimens here and there. Fall foliage tends to carry nice golden hues while, like many sedges, you may see some wintergreen depending on local climate.
Carex radiata (eastern star sedge) Photo courtesy of North Creek Nurseries
Carex rosea (curly wood sedge) and Carex radiata (eastern star sedge)
They look almost the same and have nearly identical ranges, but the difference is rosea may have more adaptability – from dry to moist and is commonly found in more upland sites – whereas radiata prefers more consistent moisture (but not wet). The “easiest” way to tell them apart is by putting a magnifying glass over their blooms.
Carex vulpinoidea (fox sedge)
While this aggressive spreader adores moist sunny sites, I’ve been experimenting with it on dry or lightly-irrigated sites. The thinking is that tougher conditions may slow down its aggressive nature just enough to allow forbs to get established and compete. I like it because, aesthetically at least, it’s a somewhat larger version of prairie dropseed (Sporobolus heterolepis). But unlike the relatively behaved clumper that is dropseed, fox sedge will more easily create the green mulch I long for as it seeds around. We’ll see.
Carex praegracilis (clustered field sedge)
In the eastern Plains and upper Midwest this rhizomatous species might be used more in rain garden and bioswales, whereas in the west it’s a sod-forming, lawn alternative that’s occasionally mowed short. That should clue you in on its potential adaptability and uses. It will flop when it gets tall in wet conditions, but that’s part of its charm, too.
Photo courtsey of Benjamin Vogt / monarchgard.com
As with any garden, but especially one layered with green mulch, it’s critical to match the plants to one another. That means being considerate of their sociability (how they reproduce) and what’s going on underground. Carex root zones are fibrous, which makes them well-suited to slowing erosion, amending soil, and soaking up water. But those dense root zones may also make it a bit harder for some forbs to compete and do well. So my suggestion would be to use forb species that spread by rhizome and those that use bulbs, corms, or have deep tap roots. Basically, the goal is to allow plants to compete and thrive at different levels above and below the soil line. Of course, the best way to learn what grows well together is to find some wild plant communities and catalog the species, as well as exploring resources on your local ecoregion. From a management standpoint, what’s really wonderful about sedge is that most of the time you can leave them in the spring – no cut down or tidying up is usually required.
In the end, using sedge as a green mulch will provide countless ecosystem services as well as providing a pleasing green continuity along the ground plane, which will make the garden look more intentional. Are you ready to get sedgy?
Carex pensylvanica (Pennsylvania sedge) and Athyrium filix-
femina (common ladyfern), Blue Ridge National Park, NC.
Photo © Izel Plants, 2018
Izel Plants Notes:
Carex is one of the most widely distributed genera of plants. Here at Izel Native Plants, we have offered close to 100 species of sedge over the years. With so many to choose from it is difficult to name our favorites, let alone write about all of them in a blog post, and we encourage to browse our website for more, and exciting options:
How do you know you’re dealing with a sedge and not a grass or a rush, which look very similar? You might have already heard of the following rhyme that makes it easy to remember how to tell them apart:
“Sedges have edges, rushes are round. Grasses have nodes all the way to the ground”.
What is being described is the identifying characteristic of the culm (flowering stem) of each group. Because a picture is worth a thousand words, look at the visual clues below. Keep in mind that the cross section of the grass does not illustrate the nodes, but focuses on the hollow culm sheathed by the leaves that connect to them.
Benjamin Vogt owns Monarch Gardens LLC, a design firm based in Nebraska which also offers online classes and consults. Benjamin is the author of A New Garden Ethic: Cultivating Defiant Compassion for an Uncertain Future, as well as Prairie Up: An Introduction to Natural Garden Design (fall 2022).
