by Jan Bower, UC Master Gardener
In 2013, a dedicated group of volunteers designed and installed a dry stream bed in the Waterwise Garden of Central Park Gardens. Dry stream beds have become popular as part of the environmental effort to transform lawns into drought-tolerant landscape. A dry stream bed mimics a natural watercourse and provides an artful landscape design feature. Stones and boulders are placed in and along a meandering channel or gully to look as if the force of water put them there. Along the edges are planted ferns, ornamental grasses, sedges, and small shrubs that give the stream a natural look and a cooling effect as they blow in a breeze. Although stepping stones, waterfalls, and even bridges can be incorporated into the design, the dry stream bed in Central Park Gardens is quite simple, with a couple of meandering curves running diagonally through the Waterwise Garden. The dry steam bed serves as a valuable educational tool for UC Master Gardeners to use when they give on-site community workshops on xeriscaping and Mediterranean gardening.
Why would you build a dry stream bed?
If you have an area of your landscape that is soggy, dry, hot, too shady, too sunny, or the soil is unfavorable, a dry stream bed may solve your problem. It can reduce topsoil erosion in areas where there is a lot of runoff from heavy rains, correct a seasonal drainage problem, or funnel excess water flow to a stormwater outlet or pond. With water becoming a scarce commodity and water rates increasing, reduced water use is being encouraged. A dry stream bed is an ideal replacement for a thirsty lawn or plants because it uses rocks, which add a natural looking element to your landscape. During the rainy season, the channel will fill with water, and you will have a real stream in your yard – but alas, no fish! Besides the practical aspect, dry creek beds can be attractive. In fact, some gardeners with absolutely no landscape problems build dry creek beds just because they like their decorative look.
Where would you build a dry stream bed?
Before creating a dry stream bed, look at some natural creek beds and observe the positions of the rocks and the overall scale of the beds. Notice how natural streams widen on the bends, and how boulders remain in the middle of the stream, while smaller rocks wash to the sides. If you have a slope or a drainage pipe, this is the place to begin your dry stream bed. A dry stream bed looks best if it follows an existing slope or a change in elevation, even if it’s not a natural feature of the landscape. It should also follow a meandering or curving path rather than a straight line. If there is a large landmark that you want to use as a focal point, build the mouth of the dry stream bed there, or have the headwaters appear to come from behind a large boulder or group of plants. Also keep in mind that natural creek beds are usually wider than they are deep. A ratio of 2:1 should look about right. For example, if you want a dry stream bed to be about four feet wide, make it about one foot deep in the center.
How would you build a dry stream bed?
First, determine how much area you want to use for your dry stream bed. For some, just a few feet will be ideal; others may want to cover an entire area. Define the shape of the dry stream bed by laying it out with a hose or a rope and mark the edges with landscaper’s paint. Remove any grass, weeds, roots, or other vegetation, and dig the channel along your mark as deep as you like, maintaining about a 2:1 ratio as described above. A rototiller can help dig the trench. Move the excavated soil to other parts of the landscape or mound it up along the sides of the channel to create planting banks. Tamp down the excavated soil with a tamping tool. Some landscapers like to line the channel with landscape fabric to prevent weeds from popping up; others prefer not to do this because the fabric can become exposed over time, particularly with a heavy rain. If you use landscape fabric, tack it down with fabric pins or garden staples and cover it with a layer of sand, gravel, or river rock. If the stream bed will carry water, the bed needs to be reinforced with stiff wire netting, and the rocks installed into the netting with at at least 2 inches of mortar to hold them in place. Fibreglass can also be used to hold rocks in a stream bed, but this is an expensive and more complicated process, and should probably be done by a professional. The advantage of using fibreglass is that the stream bed will last longer – probably a lifetime!
Choose rocks, stones, and gravel in a variety of shapes and different sizes, combining smooth river rocks with small water-washed boulders to make it look natural. Usually the rocks are in tones of grey and tan and mix well, but some colorful pebbles can also be added for decoration. Rocks should be in scale with the size of your yard and stream bed. For example, a small stream bed should not be overwhelmed with huge boulders. Place rounded small and medium-sized river rocks along the center of the channel to create the effect of rapids or ripples, but avoid organizing the rocks in any pattern. Add some larger rocks or boulders along both edges and in the middle of the stream to create an appearance of their being too heavy for the current to move. Put large boulders at the bends in the stream and to disguise the headwaters. For a more natural appearance, put some rocks on top of each other or partially bury them. Move the stones around to get the look you want and to showcase the rock’s best side. Fill any spaces with more river rocks. Spread fine gravel at the lower end of the dry stream bed to create the appearance of naturally-deposited sediment.
After you build a dry stream bed, you can dress it up a bit. For instance, plants, such as lomandras and dianellas, will soften the edges, while small palms, dwarf clumping bamboo, and birch trees, leaning over the stream bed, create a very pretty picture. The use of native California plants adds to the natural appearance of the dry stream bed and reduces maintenance. To further enhance the bed, add a piece of driftwood, a gnome, or a moss-covered log. If you want to grow moss on any of the rocks, spray them with buttermilk and place them in a moist, shady area. Aquatic plants work well if you have dug a sinkhole or hollow somewhere in the creek bed channel, and it fills with water.
What You Will Need:
Fabric pins or garden staples
River rocks and boulders
Wheelbarrow for mixing the mortar