Q. I've seen beautiful tufts of Mondo Grass growing among flowers, shrubs and trees in shopping center planters and have admired the pretty purple flowers that bloom amidst the dark green blades. But the little purple flowers on the Mondo grass I have at home are puny; I have to really hunt to find them. And even though I cut my grass short every Spring, the lush green leaves are encroaching on my other plants by summer. I'm also finding more and more OTHER grasses growing among the Mondo, and it's getting harder to keep the unwanted plants at bay. How do I properly grow this beautiful ornamental grass?
- ---Erin in Hopewell, NJ
- ---Liz in Spotsylvania, VA
Let's begin with a discussion of basic, normal sized Mondo grass. The leaves are dark green and look a lot like those of an ornamental grass. Although Mondo grows in clumps, those clumps send out underground runners that slooowly spread laterally to gradually fill in the areas in-between, giving the appearance—after a few years—of something a bit like a lawn. The basic type grows to around eight inches in height, but the leaves tend to bow down, giving it a shorter appearance and leading to a more full, lawn-like look. Mondo grass lawns need no mowing, tolerate pretty deep shade and are very drought resistant.
Mondo grass is also used to fill in areas between pavers and stepping stones. The dwarf varieties—named versions of O. japonicas that range in height from a tidy two to four inches—are especially good at this. Now, you'd think that grass-like plants that size would make a perfect lawn substitute, but dwarf Mondo grasses are notoriously slow to spread, and you'd have to plant them as thick as sod to keep weeds from overwhelming them in a big lawn-like planting.
Although it's most widely used as a groundcover in shady areas, sources tend to call Mondo a 'sun or shade' plant. But as I've explained in the past, 'full sun' means different things depending on where you live, and the garden experts at Southern Living magazine (who know a lot more about hot weather gardening than I do) warn not to plant it in areas that receive a fair amount of hot, direct sun.
The little purple flowers lusted after by our New Jersey listener appear on very short spikes, and are generally lost inside the leaves; so I'm guessing that placement had a lot to do with her shopping center experience. Mondo grass that's planted higher—in a container or dramatically raised bed—will appear to have more visible flowers, as will individual specimens that don't have the leaves of other plants overlapping them. It's much easier to achieve this look in a commercial bed that's probably planted fresh every year than in a home landscape.
The annual mowing she mentions is also probably detracting from its potential appearance, as well as opening it up to weed invasion and maybe even forcing it to spread faster into those unwanted areas. So no more mowing. But the habit of basic Mondo is to slowly spread, and if she wants it to stay exactly where she plants it, she needs to install edging around a desired area of plants, or tear out what she has and replace it with a similar but black-bladed cousin that doesn't move around.
That would be so-called 'black Mondo grass', which despite its common name, is a different species of plant within the Ophiopogon genus. (Its scientific name is O. planiscapus 'Nigrescens'.) The leaves are about as close to true black as you'll see in the plant world, and it grows about as tall as true Mondo grass, but it doesn't spread much at all, behaving a lot more like a true ornamental grass. (So it wouldn't fill in to give you a black lawn; sorry, Addams Family fans.)
And Black Mondo can also be grown a little further North than regular Mondo grass (which is frost hardy, but wouldn't survive a far Northern winter).
Black Mondo may also be the best choice for Liz near D. C., who wants height but not spread. Otherwise, some decent edging should be enough to keep the basic type where you want it. Because,while it does spread, I wouldn't call Mondo grass invasive or aggressive. Ah, but some other members of the Ophiopogon genus, like Aztec grass, are aggressive and highly invasive. Be careful you don't get one of them mislabeled as Mondo.