Rain Gardens are intended to be an attractive and environmentally sensitive addition to residential, commercial and municipal properties. The main objective is to reduce storm water runoff from impermeable surfaces such as driveways, parking lots and rooftops, thereby reducing erosion and sedimentation of local streams and rivers. A secondary objective or benefit is the removal of pollutants in the water via absorption and metabolism by plants. The typical rain garden detains the storm water in a pond-like or detention basin structure that has been planted with site appropriate plants. The basin allows the water to perk into the ground and enhance deep water recharge while the plants remove many of the pollutants and help mitigate the storm water through transpiration.
Rain gardens look attractive when newly planted, but can and often deteriorate over time with the invasion of unattractive weeds and a resulting decline in vigor from the ornamental plantings as they become ‘choked-out’. The intent at Rutgers Gardens was to design and develop a garden that had all the positive environmental aspects, yet remained attractive throughout the year with minimal maintenance. Another detail that is often overlooked is the location of this feature. As previously noted, it should be located no closer than 10 feet from a building, but this does not preclude placing it in a location that is more befitting and piping water to the feature. Focus upon these two details resulted in a water feature with a 750 gallon cistern that is recharged via the rain water from the roof of a shed located 30′ uphill of the garden. The water is circulated through the water feature via a pump at the bottom of the cistern through a series of bogs, over a waterfall and back into the cistern. The waterfall above the cistern is essential for permitting aeration of the water. Two layers of 2″ thick filter material lie above the cistern to capture any sediment and debris that would otherwise accumulate in the cistern.
During heavy rains, the cistern is not only recharged, but the excess water spills over into the lowest basin which surrounds the cistern, permitting deep water recharge. The lowest basin is planted with Tussock Sedge (Carex stricta), Grays Sedge (Carex grayii), and two forms of water Iris (Iris versicolor and Iris virginica), all plants that can tolerate typical garden soil moisture along with periods of inundation for up to several weeks or even months at a time! This basin also has large stepping stones, which allows visitors to better experience the garden, to see the waterfall and to access the patio and stone bench.
The basins above the cistern and along the water rill serve as a series of bog gardens. The first and smallest basin is planted with Royal Fern (Osmunda regalis), the second has a contained water rill with a planting of Ostrich Fern (Matteuccia struthiopteris) outside the rill, while the third basin has a planting of Purple Pitcher Plants (Sarracenia purpurea), Cardinal Flower (Lobelia cardinalis), and Carex grayii. The plantings of the bog gardens naturally transpire and reduce the water while absorbing nutrients. Flooding the area and creating bogs also reduces the amount of soil that can potentially give rise to weeds. The water which passes into the first basin via the white PVC pipe is not the only location or source at which the recirculating water enters the bogs! From the base of the water rill in the second basin and also just before the waterfall of the third basin are additional points of introduced water. This permits the water flow and waterfalls to increase in intensity with each consecutive basin.
In between the first and second garden is a circular paved area, through which a water rill passes. This brings the water into closer contact with the visitor and, similar to the stone stepping stones, makes the visitor feel more as a participant in the Rain Garden, not just an observer. This paved area is part of a turf pathway that leads visitors back towards the Pollinator Garden and eventually to Helyar Woods.
Thoughts and Review
Based solely on square footage of the roof (528 Ft2) and the size of the last basin (24′ diameter), which can hold an average of one foot of water, this water feature could accept a structure that is 6 times the size of the shed. However, since water is constantly being transpired by the plants and evaporated by the waterfall, a shed that was 8 times the size could probably be supported! The receptacle for the rain chain on the shed was also enlarged from 18″ to 36″ in diameter. During strong winds, the water actually blew off the chain and missed the receptacle! However, these are minor and the garden has proven to be a great hit with the community. During the summer of 2017, additional Sarracenia or Pitcher Plants were added to the bog—an addition requested by all the children that come through on tours and want to see ‘bug-eating’ plants (alias “Audrey” of Little Shop of Horrors).
Nature’s Rain Garden
Rain Gardens are not new to the world. In nature, Rain Gardens are found in the forms of Vernal Ponds, Swamps or Bogs, and to a lesser degree, flood plans. All of these areas consist of vegetated areas that accommodate excess storm water and then allow it to either slowly perk into the ground or return to streams via sheet flow. Vegetation in these areas has become acclimated to prolonged periods of inundation, followed by equally prolonged periods of drought. Just the type of plant that is needed for the built Rain Garden!
When you install your plants, remember that they most likely have become adapted to growing under nursery conditions. As a result, they will initially not yield a favorable response to soils that remained water logged for weeks on end. Install the plantings during the months that are typically not forecasted to receive large rainstorms. In NJ, late May through August would be ideal. If you the timetable is such that you need to install the plants during the wetter months, you can either wait to hook up the Garden to the water source at a later date or you can try to plant the crowns of the plants slightly high, to improve drainage and aeration of the root ball. Planting in late October through winter is not suggested.
Below is a listing of plants which are appropriate for use in Rain Gardens. In some instances, selections are noted for those wishing to include plants that have been selected for improved flowers, form or fruit.
Plants Adjacent to the Rain Garden at Rutgers Gardens
Shrubs and Trees
- Betula nigra – River Birch (also appropriate for use in Rain Gardens)
- Calycanthus floridus ‘Athens’ – Athens Carolina Allspice
- Chionanthus virginicus – Fringe Tree (also appropriate for use in Rain Gardens)
- Itea virginica – Virginia Sweetspire (also appropriate for use in Rain Gardens)
- Magnolia virginiana – Sweetbay Magnolia (also appropriate for use in Rain Gardens)
- Nyssa sylvatica – Black Tupelo (also appropriate for use in Rain Gardens)
- Xanthorhiza simplicissima – Yellowroot
- Chelone lyonii ‘Hot Lips’ – Hot Lips Turtlehead (also appropriate for use in Rain Gardens)
- Chrysogonum virginianum – Goldstar
- Eupatorium coelestinum – Hardy Ageratum (also appropriate for use in Rain Gardens)
- Heuchera villosa ‘Autumn Bride’ – Alum Root
- Adiantum pedatum – Maidenhair Fern
- Carex amphibola – Eastern Narrowleaf Sedge
- Carex pennsylvanica – Pennsylvania Sedge
Plants Appropriate for Planting in Rain Gardens
Shrubs and Trees
- Aronia arbutifolia – Red Chokeberry (‘Brilliantissima’ is an improved form that is on the market)
- Cephalanthus occidentalis – Buttonbush (‘Sputnik’ is a form with larger flowers that appear over a longer bloom period)
- Clethra alnifolia – Summersweet (there are numerous compact and pink flowered forms available)
- Fothergilla gardenia – Dwarf Fothergill
- Ilex verticillata – Winterberry Holy (numerous selections for red, yellow or golden fruit are on the market)
- Salix alba ‘Britzensis’ – Flame Willow
- Vaccinium corymbosum – Blueberry (numerous selections are on the market for improved fruit. Make certain you plant two selections for best fruit set)
- Viburnum dentatum – Arrowwood Viburnum (Chicago Lustre® is an improved form)
- Viburnum nudum – Smooth Witherod (Brandywine™ and Winterthur are two improved forms)
- Asclepias incarnata – Swamp Milkweed
- Chelone glabra – Turtlehead
- Eupatorium dubium – Joe Pye Weed
- Helianthus angustifolius – Swamp Sunflower (numerous selections abound for more compact habits)
- Iris versicolor – Blue Flag Iris
- Iris virginiana –Virginia Iris
- Lobelia cardinalis – Cardinal Flower
- Lobelia siphilitica – Blue Lobelia
- Sarracenia purpurea – Pitcher Plant (needs soil which does not become excessively dry)
- Spiranthes cerna – Ladies Trusses Orchid
- Veronicastrum virginicum – Culver Root (‘Lavender Towers’ has pale lavender flowers)
- Matteuccia struthiopteris – Ostrich Fern
- Osmunda cinnamomea – Cinnamon Fern
- Osmunda regalis – Royal Fern
- Carex grayii – Grays Sedge
- Carex muskingumensis – Palm Sedge (‘Oehme’ is a variegated form)
- Carex stricta – Tussock Sedge
- Panicum virgatum – Switch Grass