Rain gardens are specially designed depressions in the landscape that capture and filter stormwater runoff from impervious surfaces such as roofs, driveways, and sidewalks. The main goal of a rain garden is to reduce runoff, improve water quality, prevent erosion, and recharge groundwater. While taller perennials, shrubs, and ornamental grasses often get attention in rain garden design, groundcovers play an equally critical role. These low-growing plants can stabilize soil, enhance aesthetics, support wildlife, and even improve the long-term health of the garden.
But are groundcovers truly suitable for rain gardens? The answer is a resounding yes, provided you select species that tolerate the unique moisture conditions of these landscapes. Let’s explore why groundcovers are valuable, how to choose them, and some practical tips for integrating them into your rain garden.
Why Groundcovers Are Valuable in Rain Gardens
Groundcovers provide several ecological, functional, and aesthetic benefits in rain gardens. Their low-growing, spreading habit makes them particularly useful in areas where soil stabilization and erosion control are essential.
1. Erosion Control
Rain gardens experience fluctuating water levels. After heavy rainfall, water flows into the garden, potentially washing away soil. Groundcovers help anchor soil with their fibrous roots, reducing erosion and sediment displacement. Plants such as Creeping Jenny (Lysimachia nummularia) or Pennsylvania sedge (Carex pensylvanica) spread rapidly and create dense mats that hold soil in place even on slopes or in areas with concentrated runoff.
2. Moisture Adaptation
A rain garden typically has three moisture zones: wet at the bottom, moderately moist in the middle, and relatively dry at the edges. Groundcovers can be chosen to thrive in each of these zones:
- Wet zone: Species that tolerate periodic standing water and saturated soil.
- Middle zone: Plants that prefer consistent moisture without prolonged flooding.
- Dry edge: Drought-tolerant groundcovers that stabilize soil on the outer edges.
This adaptability makes groundcovers ideal for filling gaps between taller plants while maintaining the garden’s functional integrity.
3. Weed Suppression
Dense groundcover layers reduce sunlight reaching the soil surface, making it more difficult for weeds to establish. This is especially valuable in rain gardens, which can be disturbed by runoff and nutrient deposition. By crowding out weeds, groundcovers reduce maintenance needs and help other plants thrive.
4. Soil and Water Quality Benefits
Many groundcovers have fibrous roots that improve soil structure, enhance infiltration, and reduce compaction. Their root systems help filter pollutants such as sediments, nutrients, and hydrocarbons from runoff, improving water quality before it reaches groundwater or streams. Additionally, some species can absorb excess nutrients, preventing algal blooms in downstream water bodies.
5. Aesthetic Appeal
Groundcovers add texture, color, and contrast to the rain garden. They soften edges, provide seasonal interest, and create a lush, finished look. Low-growing foliage can complement taller perennials and ornamental grasses, adding layers and depth to the garden. Some groundcovers, like Wild ginger (Asarum canadense), even produce attractive flowers in spring.
Choosing the Right Groundcovers for Rain Gardens
Selecting groundcovers for a rain garden requires attention to moisture tolerance, sun exposure, growth habit, and maintenance requirements. Here are the key considerations:
1. Moisture Tolerance
- Bottom Zone (Wettest): Groundcovers here must withstand temporary flooding. Examples:
- Marsh marigold (Caltha palustris) – Thrives in saturated soil.
- Creeping Jenny (Lysimachia nummularia) – Spreads in moist conditions and tolerates occasional standing water.
- Middle Zone (Moderate Moisture): Prefers consistent moisture but not flooding. Examples:
- Wild ginger (Asarum canadense) – Shady and moisture-tolerant.
- Pennsylvania sedge (Carex pensylvanica) – Forms dense, low-growing mats.
- Edge Zone (Driest): Adapted to periods of drought. Examples:
- Creeping thyme (Thymus serpyllum) – Drought-tolerant and aromatic.
- Sedum species – Low-maintenance and sun-loving.
2. Sun Exposure
Rain gardens can vary from full sun to partial or full shade depending on the site. Always choose groundcovers that match the sunlight conditions:
- Full sun: Creeping thyme, sedums, creeping Jenny.
- Partial shade: Wild ginger, sweet woodruff.
- Full shade: Foamflower (Tiarella cordifolia), bunchberry (Cornus canadensis).
3. Growth Habit
Select groundcovers that spread to cover bare soil without overwhelming neighboring plants. Avoid aggressive species that may become invasive, such as some ivy varieties. Ideally, the groundcover should complement taller plants and fill gaps naturally.
4. Maintenance Needs
Low-maintenance species are preferable in rain gardens. Many groundcovers require minimal watering once established, resist pests and disease, and need little pruning or trimming. This makes them ideal for sustainable landscapes and long-term performance.
Benefits of Integrating Groundcovers in Rain Gardens
1. Erosion Control on Slopes
Rain gardens with slopes or side berms can experience significant soil erosion. Low-growing, dense groundcovers like creeping Jenny or sedges anchor soil and reduce runoff velocity.
2. Wildlife Support
Some groundcovers attract pollinators by producing flowers that provide nectar and pollen. Additionally, they create habitat for insects, small mammals, and even birds. This adds ecological value beyond water management.
3. Improved Infiltration and Filtration
The fibrous roots of groundcovers break up soil and increase infiltration, helping water soak into the ground faster. This reduces standing water and improves the garden’s efficiency. Simultaneously, roots filter sediments and pollutants, supporting water quality.
4. Visual Cohesion
Groundcovers create a carpet-like effect that unifies the garden, especially when combined with taller perennials, shrubs, and grasses. Seasonal color changes or flowering groundcovers can enhance aesthetics without overwhelming other plants.
Planting Tips for Groundcovers in Rain Gardens
- Prepare the Soil: Loosen compacted soil and add organic matter to improve drainage and fertility.
- Space Properly: Even low-growing plants need room to spread. Plant too closely, and competition may stunt growth.
- Consider Zoning: Plant moisture-loving species in wet areas and drought-tolerant species along edges.
- Mulch Sparingly: Mulch can help retain moisture but may inhibit spreading. A thin layer is usually sufficient.
- Monitor Establishment: Newly planted groundcovers may need supplemental watering until roots establish.
Common Groundcover Mistakes to Avoid
- Using Invasive Species: Plants like English ivy or some periwinkles can escape the garden and disrupt native ecosystems.
- Ignoring Moisture Preferences: Placing drought-tolerant groundcovers in wet zones can result in plant loss.
- Overcrowding: Planting too densely may prevent airflow, encourage disease, or hinder growth.
- Neglecting Maintenance: While low-maintenance, groundcovers still need occasional trimming and monitoring for pests.
Groundcovers are highly beneficial in rain gardens. They stabilize soil, improve water infiltration, suppress weeds, enhance aesthetics, and support wildlife. By carefully selecting species based on moisture zones, sunlight, growth habit, and maintenance requirements, groundcovers can complement taller perennials and grasses to create a cohesive, functional, and beautiful rain garden.
Choosing the right groundcovers transforms a rain garden from a simple water management feature into a sustainable, ecologically rich landscape. When integrated thoughtfully, they help the garden thrive, reduce maintenance, and provide long-term environmental benefits for both people and wildlife.
In short, groundcovers are not just good—they are often essential for the long-term success of rain gardens.
Leave a Reply