My column last month focused on how sustainable landscaping promotes biodiversity. Following are several other important components of sustainable landscaping.
In this era of water shortages, a sustainable landscape is a water-wise landscape. Here on the North Coast we have been spared the worst of the concerns about drought, but the ever-rising cost of water is itself an incentive for paying attention to water usage. The majority of plants in a water-wise landscape are drought-tolerant, a mix of natives and plants from other Mediterranean areas. The plants should be well-mulched and spaced so that when they reach maturity they cover and shade most of the ground, thus reducing water evaporation.
Adding organic matter to the soil is a powerful technique for conserving water. Organic matter excels at holding moisture; in fact, one foot of rich, moist soil holds as much water as a three-inch-deep pond covering the same area. Swales — shallow trenches laid out along landscape contours — can be sculpted to catch and retain water long enough for it to seep into the ground. This recharges soil moisture while at the same time reducing erosion.
Rain gardens — shallow, saucer-shaped depressions up to 12 inches deep that are planted with appropriate plants — use the same principle. Rainwater collects in the depression and gradually percolates into the soil, while the plants trap and filter pollutants. Good information on siting and designing rain gardens for our area can be found at ucanr.edu/mg rain gardens.
Other water-saving strategies: use efficient irrigation methods, collect and store rainwater, use permeable pavement and recycle greywater. Consider replacing a traditional lawn with one of the newer lawn mixes that require less water. Or eliminate the lawn. California offers a program that pays $2 per square foot to homeowners replacing a lawn with drought-tolerant plantings; see www.water.ca.gov/turf/index.cfm. Several local homeowners have successfully participated in the program.
Minimize inputs of fertilizers and pesticides
Fertilizers can burn and kill vegetation if applied too heavily and may encourage rapid, succulent growth that attracts garden pests — such as aphids and deer — and is vulnerable to powdery mildew. High nitrogen fertilizers also encourage opportunistic annual weeds. Studies show that plants are only able to absorb roughly 50 percent of the nitrogen fertilizer applied to farm land. The remaining 50 percent of the nitrogen escapes into the air — where it is the largest human-caused source of nitrous oxide (a major greenhouse gas 300 times more potent than carbon dioxide) — or into waterways —where it contributes to algal blooms in streams and "dead zones" in oceans. While I have not seen comparable statistics for fertilizer applied to lawns and gardens, whatever nitrogen is not absorbed likewise contributes to air and water pollution.
If we want to minimize our use of synthetic fertilizers, what are our options? We can amend the soil with compost and other forms of organic matter. We can choose plants that are well-adapted to local conditions and we can grow plants that fix nitrogen in the soil. Legumes such as fava beans are often used in rotation with food crops to fix this essential nutrient in the soil. Surprisingly, several of our native woody non-legumes also provide this service: red alder, ceanothus and pacific wax myrtle.
We can also use garden practices that support the soil food web, which is composed of earthworms and soil microorganisms — bacteria, fungi, protozoa, nematodes. Together these are responsible for many essential soil processes such as aerating, recycling nutrients and increasing nutrient availability to plants. As much as 80 percent of the nitrogen a plant needs can come from waste produced by bacteria- and fungi-eating protozoa. The soil food web can be physically disrupted by rototilling and chemically injured by high-potency fertilizers; use these practices mindfully.
Earthworms are especially important to soil health. The earthworms in one acre of good soil can move 18 tons of soil a year. In doing so, they increase the porosity and water-holding capacity of soils, break up hard soils and help bind soil particles together to create an improved texture. In addition, earthworm castings are 50 percent higher in organic material than surrounding soil and contain elevated levels of available potash, phosphate, nitrogen, usable magnesium and calcium. And, in one year, earthworms can deposit 10 to 15 tons of castings per acre.
Pesticides of all sorts, even organic pesticides, are toxic to many of the creatures we want to encourage in the garden and are potentially hazardous to humans and pets as well. A healthier alternative is a method called Integrated Pest Management (IPM). The website at www.ipm.ucdavis.edu/ is a useful guide on using IPM to deal with common home, garden, turf and landscape pests.
Use garden plants and practices that attract beneficial insects such as ladybugs, hover flies and spiders. Yes, spiders! They are responsible for up to 80 percent of biological control in gardens. The goal is a garden with a balance of "good" and "bad" insects, not an insect-free garden. Remember that the more complex the web of life in the garden, the better the garden can cope with disease and pest threats.
Go non-toxic, buy local and use recycled materials
Choose less toxic snail baits such as Sluggo and similar products. Use recycled concrete to build pathways, patios and retaining walls. Use composite lumber made from recycled plastic for decking and edging (make sure it is made from recycled rather than virgin plastic). Use downed branches and garden trimmings to make woven fences around raised beds and compost piles. Craft "junque art" from recycled items — a creative way to express yourself and personalize your garden.
To wrap it up, in our own gardens we have the opportunity to make a positive contribution to many pressing environmental problems. We can make a difference. Sustainable gardening practices are good for our gardens as well as for the larger environment. These practices create healthier landscapes and sustain us, enriching our lives by forging a strong connection to our bioregion and allowing us to witness and participate in natural cycles.
Donna Wildearth is the owner of Garden Visions Landscape Design in Eureka. Visit her website at www.gardenvisions.biz.