Forest Hills Park Rain Gardens

During the 2014 renovation, DPR installed two rain gardens in the park. One is located along Brandywine Street directly to the south of the tennis courts (Rain Garden #1). The other is east of the tennis courts next to the amphitheater (Rain Garden #2).

Rain Garden #2 underwent a rehabilitation in 2019 and will continue to need regular weeding and watering. Community members interested in learning more about the rain gardens and lending a hand can contact us at

Upon the rehabilitation project’s completion in October 2019, DPR contractor and rain garden specialist Carol Herwig filed this report:

Forest Hills Rain Garden #2 Maintenance Plan

Rain gardens are designed to take rain water, especially in storm situations, and hold it for no longer than 48 hours to keep it from rushing into and overloading the city’s sewer system, and to keep it from washing street pollutants into the sewer and our water system as well. Why 48 hours? It takes that long for mosquitoes to breed.

Rain gardens are mechanically engineered, with excavation between 18 and 24 inches. The soil removed is replaced with a specified mix of topsoil, compost and sand. The Forest Hills rain garden mix is loose but not too sandy.

Forest Hills Park’s No. 2 rain garden sits adjacent to the tennis courts, on Brandywine Street just east of Connecticut Avenue NW. It is one of two on the site; the other is to the west, parallel to Brandywine. A sidewalk runs along the No. 2 garden, going north-south. The rain garden is about 50 feet long and 20 feet wide at its broadest points, is slightly kidney-shaped and is designed to take storm water running north to south from Chesapeake Street along a terrain change.

Forest Hills rain garden #2 before cleanup

The following is intended to be a road map for understanding and maintaining this valuable DC Department of Parks and Recreation resource.

Rain gardens are site specific. This garden serves as a retention site for the runoff from the playground and a grassy picnic area. It is quite shallow, more resembling a bayscaping. Its kidney shape results in part because it is adjacent to a large walnut tree. A catalpa is also nearby.

As can be seen in the before photo above, it was overrun by weeds and weed trees, especially mulberries (the children of an unmaintained parkland area nearby on Brandywine).

Volunteers cleaning up on September 21, 2019

Once this garden was cleared of weeds and walnuts on September 21st, 2019 by a group led by two Girl Scouts working on their silver badges, their parents and neighbors, little of value was left – three red-twig dogwoods and two small stands of Joe Pye weed. Of note, volunteers didn’t just cut down the mulberries; they chopped them out with a pickaxe.

The next step was to replant the garden, with the same crew of volunteers, on October 5, 2019.

The Girl Scout volunteers planting on October 5, 2019

To begin, we spread 10 bags of Leafgro to give the garden some fresh nutrition. We then installed two flats of Joe Pye weed, two flats of mountain mint, one flat of Senecio (groundsel), a flat of goldenrod and a flat of Juncus, a reed-like grass. The garden was then watered by running hoses from the apartment building across Brandywine to the south, an arrangement negotiated by a neighbor and volunteer. This arrangement, it is hoped, will continue through this droughty fall and through next summer.

A drawing of the garden, following completion of planting, has been provided for reference and future maintenance.

Rain garden planting drawing done on site. A more detailed drawing is below.

The maintenance plan:

1.Patrol the garden regularly for mulberry seedlings. This is an aggressive weed tree; controlling it is integral to the long-term success of this rain garden.

Carol Herwig (right) with one of the mulberries.

2. Water regularly. Although rain gardens are sometimes billed as maintenance-free, that is inaccurate. New plantings need to be watered regularly (weekly, with exceptions for rainy periods) for the first two years. In addition, in times of droughts, such as we observed this late summer, a watering schedule of every week or two should be established. Also because this rain garden is shallow, extra vigilance is needed. Watering should be relatively easy: There is a hose spigot on the side of the apartment building, which allows the hose to run across Brandywine. The custodian appreciates the efforts – he said he takes his children to the park frequently. Hand-watering is ideal, but a small watering ring (they cost about $2-$3) attached to the hose could allow volunteers to do maintenance on one end, while watering the other.

Watering the rain garden after the October 5, 2019 planting

3. Weeding, at least on a quarterly basis. The garden should be inspected for winter weeds (we saw a lot of smart weed this fall) and weed trees in mid-to-late March and a weeding event should be scheduled. Additional weeding events should be planned for mid-June, early August and late September.

4. For interested volunteers, Casey Trees offers a Weed Warriors class. Typically, these are held in mid-summer.

5. Protect the edges with a buffer of wood chips. This is being done this fall.

In the Washington area, there are three to four distinct seasons for weeds. Winter weeds such as chickweed and henbit appear first, Then come vines such as porcelainberry, plus creeping grasses such as Bermuda grass and crabgrass, and mugwort. Bindweed, ragweed and nightshade thistles show up in late summer. A guidebook, such as Plant Invaders of Mid-Atlantic Natural Areas from the U.S. Fish and Wildlife is helpful. So is Wild Urban Plants of the Northeast by Peter Del Tredici.

In this garden, invasive plants to watch out for: mulberry, porcelainberry vine and bindweed, and Bermuda or duck grass.

Note: For the nearby No. 1 rain garden, we are working with the STEM program at nearby University of the District of Columbia, for maintenance and related projects. This is in the beginning stages.

The plantings we found:
1. Three red twig dogwoods, they need to be pruned after the first frost.
2. Two stands of tall Joe Pye weed.
3. Thimbleweed, both native and non-native
4. A small black cherry tree, growing in the center.
5. The walnut tree.

The plantings we added. All are drought tolerant and ideal for rain gardens.
1. Two flats of mountain mint, for pollinators, fragrance and density of planting
2. A half-dozen rudbeckias for color (yellow) and naturalizing abilities.
3. A dozen goldenrod for late summer flowers, fall color and pollinators
4. Two flats of Joe Pye weed (a smaller cultivar) for spring and summer flowers and pollinators.
5. A flat of Senecio, with its yellow flowers and drought tolerance.
6. A flat of Juncus, a weed-like grass, for its strong, climbing growth habit and bright green color.

Rudbeckia, AKA black-eyed Susans

The goal of these plantings and the maintenance is to have a densely-planted space that will shade out, crowd out and be generally inhospitable to common weeds. It will flower from spring through fall, welcome butterflies, bees and other pollinators to an urban setting, welcome children and other visitors to the site and be a place of respite.

To come: a picture of the garden in spring 2020.

Carol Herwig
October 13, 2019


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