Mertens’ Rush

Mertens’ Rush: The Unsung Hero of Wetland Gardens

If you’ve been searching for a native plant that thrives in those perpetually soggy spots in your garden, meet Mertens’ rush (Juncus mertensianus). This understated perennial might not win any beauty contests, but it’s exactly the kind of hardworking plant that makes naturalistic and restoration gardens truly shine.

What Is Mertens’ Rush?

Mertens’ rush is a grass-like perennial that belongs to the rush family (Juncaceae). Despite its common name, it’s not actually a true grass – it’s what botanists call a graminoid, which includes rushes, sedges, and other grass-like plants. This rhizomatous perennial grows to about 0.9 feet tall and spreads moderately through underground stems, creating naturalistic colonies over time.

The plant produces fine-textured green foliage with small, inconspicuous purple flowers in late spring, followed by brown seeds in summer. While it won’t stop traffic with flashy blooms, its subtle beauty lies in the graceful, upright texture it brings to wet areas where many other plants struggle.

Where Mertens’ Rush Calls Home

This tough little rush is impressively widespread across western North America. You’ll find it naturally growing from Alaska down through Canada (Alberta, British Columbia, Saskatchewan, Yukon, and Northwest Territories) and throughout much of the western United States, including Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, South Dakota, Utah, Washington, and Wyoming.

The fact that it thrives from the frigid north to the southwestern deserts (in appropriate wet microhabitats) tells you just how adaptable this plant can be – as long as you give it the moisture it craves.

Why Your Garden Might Love Mertens’ Rush

Here’s where this humble rush really shines: it’s an obligate wetland plant, meaning it almost always occurs in wetlands. If you have areas in your landscape that stay consistently moist or even occasionally flood, Mertens’ rush could be your new best friend.

Perfect for:

• Rain gardens and bioswales
• Pond and stream margins
• Naturalistic wetland plantings
• Native plant restoration projects
• Areas with poor drainage that challenge other plants

The plant’s moderate growth rate and rhizomatous spreading habit make it excellent for erosion control in wet areas, while its fine texture provides lovely contrast when planted alongside broader-leaved wetland plants.

Growing Conditions: Keep It Wet!

Mertens’ rush is refreshingly straightforward about its needs: it wants water, and lots of it. This plant has high moisture requirements and low drought tolerance, so don’t even think about planting it in that dry, sunny spot where your lavender thrives.

Ideal conditions include:

• Soil: Adapts to coarse and medium-textured soils (avoid heavy clay)
• pH: 6.0 to 8.0 (slightly acidic to slightly alkaline)
• Sun exposure: Full sun to partial shade
• Water: Consistent moisture to seasonal flooding
• Temperature: Hardy to -33°F (roughly USDA zones 3-8)

One of the rush’s superpowers is its high tolerance for anaerobic (low-oxygen) conditions, which makes it perfect for those waterlogged soils where other plants literally can’t breathe.

Planting and Care Tips

The good news? Once established in the right conditions, Mertens’ rush is relatively low-maintenance. Here’s how to set it up for success:

Getting Started:

• Plant in spring after the last frost
• Space plants about 18-24 inches apart (you can plant 2,700-4,800 per acre for larger installations)
• Can be propagated by seed, bare root, or sprigs
• Seeds are tiny – there are about 45.4 million per pound!

Ongoing Care:

• Maintain consistent soil moisture – never let it dry out completely
• Minimal fertilization needed (medium fertility requirement)
• No pruning necessary, though you can cut back old foliage in late winter
• Be patient – seedling vigor is low, so establishment takes time

Wildlife and Ecological Benefits

While Mertens’ rush flowers are wind-pollinated rather than insect-pollinated, the plant still provides valuable habitat structure for wildlife. Its dense growth provides cover for small animals, and the seeds may be eaten by various birds. In wetland ecosystems, it plays an important role in stabilizing soil and filtering water.

Is Mertens’ Rush Right for Your Garden?

This native rush is ideal for gardeners who:

• Have consistently wet or seasonally flooded areas
• Want to create naturalistic, low-maintenance plantings
• Are working on habitat restoration or rain garden projects
• Appreciate subtle, fine-textured plants over flashy flowers
• Live within its native range and want to support local ecosystems

However, skip Mertens’ rush if you:

• Only have dry or well-drained planting areas
• Prefer formal garden designs with controlled plant spread
• Want immediate visual impact from colorful flowers
• Can’t provide consistent moisture

The Bottom Line

Mertens’ rush may not be the star of your garden show, but it’s exactly the kind of reliable, native supporting actor that makes naturalistic landscapes work beautifully. If you’ve got wet spots that challenge other plants, or you’re working on a restoration project, this adaptable rush deserves serious consideration. Just remember: keep it wet, give it time to establish, and it’ll reward you with years of low-maintenance, ecologically valuable growth.

Sometimes the best garden plants are the ones that simply do their job well – and Mertens’ rush does exactly that.