PHOTO: Tom Potterfield/Flickr
Rain gardens, also called infiltration basins, are shallow, level-bottomed depressions in the soil where plants grow that are appropriate for harvesting water on flat or gently sloping land. Popularly used to capture and slow storm water from surfaces that may be polluted, such as roadways and rooftops, they encourage infiltration. As the water infiltrates the ground, it is slowed, filtered and cleaned, causing storm water runoff to be reduced. Rain gardens can also be used to passively collect rainwater as it moves across a landscape.
It’s common to plant rain gardens with deep-rooted, perennial, native wildflowers, whose roots encourage the filtration process. But this is just the tip of the iceberg for rain garden uses. Trees and other perennial plants, including several edibles, can be irrigated using rain gardens. In drylands, the rain garden basins can be utilized as water-harvesting tree wells, which can reduce water needs by up to 50 percent. In areas with sufficient or excessive rainfall, the berm around the perimeter of the basin can be planted with perennials that will encourage rainwater absorption without getting wet feet.
Deep, thirsty roots and a tolerance for wet feet make the following edible perennials good candidates for a productive rain garden. However, while all of these edibles can tolerate root saturation temporarily, they will not enjoy long-term root soaking. For this reason, it’s important to locate and construct your rain garden properly so that it drains within 12 hours after filling up. (If it doesn’t, your “rain garden” is really more of a pocket pond, a vernal pool that fills up during the wet season.)
1. Asparagus (Asparagus officinalis)
Asparagus will grow in USDA hardiness zones 3 to 8. Wild asparagus is often found growing in ditches where water might seasonally collect. After making this discovery, I’ve grown cultivated asparagus in several places where water collects, and it has thrived. In my temperate zone-6 climate, asparagus has grown best in the basin rather than on the berm.
The roots of a mature asparagus patch can extend up to 6 feet deep and can be extremely helpful in slowing and absorbing rainwater.
2. Rhubarb (Rheum x cultorum)
Rhubarb grows in hardiness zones 3 to 8. It doesn’t do well inside the basin, but it will thrive on the berm or on a downhill slope below the berm, where it has access to moisture without getting wet feet. The thick and fibrous roots will typically grow 8 feet deep and will stabilize the berm, slow down water flow and reduce erosion.
3. Strawberry (Fragaria x ananassa)
Strawberries are a common addition to the home garden and grow in hardiness zones 3 to 10. Strawberries are similar to rhubarb in that their fibrous roots are excellent at stabilizing soil and reducing erosion. Their 2-foot-deep roots do best when planted on the berm.
4. Spicebush (Lindera benzoin)
Spicebush is a native, deciduous shrub that grows in zones 4 to 9. Naturally growing in moist, woodland areas, this deer-resistant plant will thrive in the moist environment of the rain garden basin. It likes partial shade, and the shrub will attract spicebush swallowtail butterflies. The berries are used as an alternative to allspice and pair well with apples.
5. Red Raspberry (Rubus idaeus var. strigosus)
While cultivated red raspberries (zones 3 to 9) will work satisfactorily in the rain garden, wild American red raspberries (zones 2 to 6) will work even better. Enjoying wet feet, they will do well either on the berm or in the basin.
6. Elderberry (Sambucus canadensis)
Elderberry grows in zones 3 to 10 and will produce flowers and berries that both humans and wildlife will enjoy. It does well in the basin of the rain garden, where this large, 12-foot-tall shrub will quickly absorb excess rainwater.
7. Highbush Cranberry (Viburnum trilobum)
Highbush cranberry is a native shrub that grows in zones 2 to 7. While the red berries are the size and shape of common cranberries, the two plants aren’t from the same family. Highbush cranberries are often used in jams and jellies and aren’t well-liked by birds, which means an easy harvest for you. This large, 12-foot-tall shrub, like elderberry, will enjoy the moisture of the rain garden basin and will quickly absorb excess rainwater.
Consuming Edibles From A Rain Garden
As mentioned above, rain gardens are sometimes used in areas where storm-water runoff may be polluted. While you are wise to be concerned, contaminants tend to accumulate in the leaves and roots of plants rather than the fruits. Because of this, all of the berry crops listed above would be still be safe to eat in contaminated sites. In fact, more and more orchards are being established in polluted urban soils precisely because the contaminants do not accumulate in the fruits.
For sanitation purposes, avoid contact with surface water that exists in the rain garden directly after rain. Refrain from harvesting any items that might come into direct contact with the surface water. For this reason, strawberries grown on a rain garden berm, where the plants do not come into contact with the surface water, are also safe to eat. Berries from woody plant species, such as spicebush, raspberry, elderberry and highbush cranberry, are completely safe to harvest and eat because they grow higher off the ground and therefore the berries do not have contact with the soil surface. Because asparagus and rhubarb crops include harvesting the stems of the plants where contaminants may accumulate, I recommend that these only be grown in rain gardens collecting safe water.
For more information on constructing an appropriate rain garden for your situation, see Rainwater Harvesting for Drylands and Beyond, Volume 2: Water Harvesting Earthworks (Rainsource Press, 2007). You’ll find instructions for various rain garden uses and calculations of capacity and volume.
Find more ways to save water around the farm:
- Water Your Garden Using a Rain Barrel
- 4 Ways to Nourish Your Soil During Drought
- What Is a Swale?
- 6 Reasons Backyard Compost is the Best Soil Enhancer
- Prevent Disease and Dried-Out Soil with Plasticulture