Knotgrass: A Hardy Wetland Ground Cover for Challenging Sites
If you’ve been struggling to find a plant that can handle consistently wet soil conditions, meet knotgrass (Paspalum distichum) – a tenacious perennial grass that thrives where many other plants fear to tread. While it may not win any beauty contests, this unassuming ground cover has some serious staying power in wet, challenging locations.
What Exactly Is Knotgrass?
Knotgrass is a low-growing, mat-forming perennial grass that spreads by stolons (above-ground runners) to create dense carpets. Despite its humble appearance, this hardy grass has quite a few aliases in the botanical world, including Digitaria paspaloides and Paspalum paspaloides. At maturity, it typically reaches less than a foot tall, making it a true low-growing grass option.
The plant features fine-textured green foliage that remains relatively dense throughout the growing season. Don’t expect showy flowers – knotgrass produces small, inconspicuous green blooms in late summer that won’t add much ornamental value to your garden.
Where Does Knotgrass Call Home?
Knotgrass is native to most of the continental United States, Puerto Rico, and the U.S. Virgin Islands. You can find it growing naturally across a vast range, from Alabama and Arizona to Washington and Virginia, plus many states in between. However, it’s considered non-native in Hawaii and some Pacific regions, where it has naturalized.
The Wet Soil Specialist
Here’s where knotgrass really shines – its relationship with water. This plant has varying wetland classifications depending on the region:
- In some areas (Atlantic and Gulf Coastal Plain, Caribbean, Midwest), it’s classified as an Obligate Wetland plant, meaning it almost always occurs in wetlands
- In other regions (Arid West, Eastern Mountains, Great Plains, Hawaii, Western Mountains), it’s considered Facultative Wetland, usually found in wetlands but occasionally in drier sites
This adaptability makes knotgrass incredibly valuable for wet, problematic areas where other plants struggle to establish.
Should You Plant Knotgrass in Your Garden?
The answer depends entirely on what you’re trying to achieve. Knotgrass isn’t going to win any awards for ornamental beauty, but it excels in specific situations:
Consider knotgrass if you:
- Have consistently wet or periodically flooded areas
- Need erosion control along pond edges or streams
- Want a low-maintenance ground cover for challenging sites
- Are working on wetland restoration projects
- Live in USDA hardiness zones 7-11
Look elsewhere if you:
- Want an ornamental, decorative grass
- Have well-draining, dry soils (it has no drought tolerance)
- Need a plant for shaded areas (it’s shade intolerant)
- Live in areas with fewer than 220 frost-free days
Growing Knotgrass Successfully
If knotgrass sounds like the right fit for your wet spots, here’s what you need to know:
Soil Requirements:
- Prefers fine to medium-textured soils
- Tolerates a wide pH range (4.9 to 8.9)
- Needs consistent moisture – high water use
- Handles salt and calcium carbonate well
Growing Conditions:
- Requires full sun (shade intolerant)
- Needs 30-64 inches of annual precipitation
- Active growing period spans spring through fall
- Rapid growth rate once established
Planting and Care:
- Can be propagated by seed or sprigs
- Seeds are routinely available commercially
- Plant density can range from about 11,000 to 43,000 plants per acre
- Minimal root depth (just 4 inches minimum)
- Medium fire tolerance
The Bottom Line
Knotgrass may not be the star of your garden show, but it’s an incredibly useful plant for specific situations. If you’re dealing with wet, challenging sites where other plants fail, this hardy perennial grass could be exactly what you need. Its rapid growth and spreading habit make it excellent for erosion control and ground coverage in wetland settings.
Just remember – this is a plant with a specific job description. It excels in wet conditions but won’t adapt to drought, and while it’s native to most of the U.S., it’s not going to provide the ornamental appeal of more decorative grasses. But sometimes, the most valuable plants are the ones that simply get the job done where others can’t.
