Streamside gardening: your garden, our shared watershed

A watershed, also known as a drainage basin, is the region of land whose rain and snowmelt drain into a specific body of water. We’ve altered our watersheds and changed how they function through a variety of land-use changes and activities, including deforestation, agriculture, urban development and suburban sprawl. The land surrounding a river or stream directly affects the stream’s flow rate and temperature, as well as the neighboring communities of plants, animals and people. On land surrounding a stream, how you garden can maintain or restore some of the functions of a healthy streamside to benefit plants, wildlife and humans.

Tips for protecting our watershed

Minimize the use of fertilizers and pesticides

Synthetic fertilizers and pesticides are designed to promote or stop biological growth, both of which alter natural ecology and are contaminants to stream health. Think before you apply, as anything you apply to your garden will eventually end up in the stream. Try using organic and slow-release fertilizers that last longer and don’t run off as easily as synthetic fertilizers. For pest control, follow the principles of integrated pest management and always start with the least toxic control measure available.

Minimize soil erosion

Often, homes along streams have lawns leading directly to the edge of the water. The shallow roots of turfgrass are not adequate to protect the bank from erosion. Every time it rains, stream banks not anchored with sufficient plant roots erode, leading to property loss. Instead of growing lawn all the way to the stream, plant native ground covers, shrubs and trees to prevent erosion. Furthermore, minimize tillage and other forms of soil disturbance to discourage the growth of annual weeds, keep the roots of native plants intact, and further reduce surface runoff and soil erosion.

Build a rain garden

Impervious surfaces, such as roofs, driveways, sidewalks and patios, prevent rain from infiltrating into the soil. If your property has many impervious surfaces and is close to a waterway, you may want to consider building a rain garden to collect and treat stormwater runoff. Rain gardens can improve the health of our watersheds by reducing flooding, filtering pollutants, recharging groundwater aquifers, and providing beneficial wildlife habitat. More information about constructing a rain garden and sample plans can be found in The Oregon Rain Garden Guide.

Protect wildlife

A wildlife-friendly streamside garden teems with birds, butterflies, frogs and other critters. It provides a protected passageway for fish and a home for animals that depend on the narrow edge of conditions between your garden and the stream channel. Your trees may be the nesting sites for water-loving birds such as herons and songbirds. Allow branches to overhang and shade the stream, making the stream more livable for aquatic organisms. If possible, allow large fallen branches to lodge within the stream. Leaf litter is one type of food for stream inhabitants, and leaving woody debris may lead to the formation of pools, required for some species of fish. Tree roots, stems, debris and limbs can slow water flow, allowing sediments to settle out and resulting in clearer water.

Manage invasive plants

Invasive plants rarely provide the same functions as native plants for providing streamside habitat. The replacement of a native streamside plant community by only one species of weed is not beneficial to wildlife and makes for a boring garden. Invasive plants may have some tempting garden qualities such as pretty flowers or an inexpensive price, but they can quickly escape your garden and invade the rest of your property, as well as areas downstream. Invasive species listed as noxious weeds by the Oregon Department of Agriculture (ODA) are generally not available for purchase in Oregon, but you can always double check before making any plant purchases by consulting the ODA’s Noxious Weed Profiles.

If you have invasive species on your land already, it’s your responsibility to manage them. For streamside gardens, keep an eye out for these invasive species and take the necessary steps to remove them:

• Japanese knotweed (Polygonum cuspidatum)
• Purple loosestrife (Lythrum salicaria)
• Yellow flag iris (Iris pseudacorus)
• English ivy (Hedera helix)
• Reed canary grass (Phalaris arundinacea)
• Himalayan blackberry (Rubus armeniacus)

Most likely, removing weeds along your streamside garden will require using several different management techniques over multiple seasons.

Pull or dig out new invasive plants as soon as you notice them so that they don’t gain a foothold. Some species, such as reed canary grass, perform poorly in shade and can be outcompeted by planting trees, which brings additional benefits to the stream. You may also want to reach out to your local soil and water conservation district, cooperative weed management area, watershed association, or county extension office for best practices related to invasive weed management.

Plant native trees and plants

When you garden along streams, remember that the groundwater table is shallow enough to interact with the roots of your plants; this is particularly true nearest the stream itself. Parts of your garden may also periodically flood. Select native plants for different areas of your streamside garden based on the availability of soil moisture during the dry summer months and the potential for flooding at other times of the year:

• Stream channels and banks are often flooded at least part of the time every winter and support largely hydrophytic (water-loving) vegetation. Soils are often rocky and difficult to plant. Plant flood-tolerant species.
• Upper banks and floodplains may be a very narrow zone in a channelized or confined stream or a wide zone in an unconfined stream. Shrub and weed competition may be intense. Soils are often sandy and/or rocky and droughty. Both flood- and drought-tolerant species may be suitable.
• Upper terrace and uplands adjacent to stream bank support primarily upland vegetation, although some water-loving plants may be found. Plant drought-tolerant species.

Here are some native plant suggestions for streamside gardens in the Pacific Northwest. Photos and more information about each of these species can be found on Oregon Flora or in “Gardening with Oregon Native Plants West of the Cascades.”

• Trees for the water's edge
  • White alder (Alnus rhombifolia)
  • Red alder (Alnus rubra)
  • Oregon ash (Fraxinus latifolia)
  • Western crabapple (Malus fusca)
  • Western red cedar (Thuja plicata)
• Trees for drier areas
  • Vine maple (Acer circinatum)
  • Big-leaf maple (Acer macrophyllum)
  • Sitka spruce (Picea sitchensis)
  • Ponderosa pine (Pinus ponderosa var. benthamiana)
  • Bitter cherry (Prunus emarginata)
  • Oregon white oak (Quercus garryana)
  • Cascara (Rhamnus purshiana)
• Deciduous shrubs for the water's edge
  • Red-osier dogwood (Cornus sericea)
  • Twinberry/bearberry honeysuckle (Lonicera involucrata)
  • Pacific Ninebark (Physocarpus capitatus)
  • Pacific willow (Salix lasiandra)
  • Douglas’ spirea (Spiraea douglasii)
• Shrubs for drier areas
  • Tall/Shining Oregon grape (Berberis aquifolium)
  • Cascade Oregon grape (Berberis nervosa)
  • Osoberry (Oemleria cerasiformis)
  • Wild/Lewis’ mock orange (Philadelphus lewisii)
  • Red flowering currant (Ribes sanguineum)
  • Nootka rose (Rosa nutkana)
  • Blue elderberry (Sambucus mexicana)
  • Red Elderberry (Sambucus racemosa)
  • Snowberry (Symphoricarpos albus)
• Flowering herbaceous plants for the water's edge
  • Camas (Camassia leichtlinii)
  • Deschampsia (Deschampsia cespitosa)
  • Monkey flower (Erythranthe spp.)
  • Skunk cabbage (Lysichiton americanus)
  • Wapato (Sagittaria latifolia)
  • Cattail (Typha latifolia)
• Flowering herbaceous plants for drier areas
  • Common yarrow (Achillea millefolium)
  • Western red/Sitka columbine (Aquilegia formosa)
  • Goatsbeard (Aruncus dioicus)
  • Douglas’ aster (Symphyotrichum subspicatum)
  • Oregon bleeding heart (Dicentra formosa)
  • Oregon iris (Iris tenax)
  • Blue-eyed grass (Sisyrinchium bellum)
  • Goldenrod (Solidago sp.)
  • Stream/pioneer violet (Viola glabella)
• Ferns
  • Lady fern (Athyrium filix-femina)
  • Deer fern (Blechnum spicant)
  • Sword fern (Polystichum munitum)
• Groundcovers
  • Bearberry/kinnikinnick (Arctostaphylos uva-ursi)
  • Beach/coastal strawberry (Fragaria chiloensis)
  • Woodland strawberry (Fragaria vesca)
  • Wild strawberry (Fragaria virginiana)
  • Oregon wood-sorrel (Oxalis oregana)
  • Northern inside-out flower (Vancouveria hexandra)

References and additional resources

• GardenSmart Oregon | Oregon Sea Grant | Oregon State University
• Guide for Using Willamette Valley Native Plants Along Your Stream from the Linn Soil and Water Conservation District
• How’s my Waterway? from the EPA
• OregonFlora Home
• Oregon Noxious Weed Profiles from the Oregon Department of Agriculture
• Solve Pest Problems (oregonstate.edu)
• Related content from OSU Extension
• Gardening with Oregon Native Plants West of the Cascades | OSU Extension Service (oregonstate.edu)
• The Oregon Rain Garden Guide | Oregon Sea Grant | Oregon State University
• Rain Gardens: Low-impact development fact sheet | OSU Extension Service (oregonstate.edu)