Your Yard and Water Quality: Simple Things Gardeners Can Do To Prevent Water Contamination

We generally view gardening as a wholesome activity that enhances our environment. But pesticides, fertilizers, and erosion from gardens and landscapes can contaminate lakes, streams, rivers, the ocean, and groundwater. Since the quality of our water resources affects our quality of life, we must learn how our gardening practices can contribute to water contamination and what we can do to reduce the threat to water quality.

We have long been aware of contamination from point sources such as factories and municipal sewage systems. Recently, we have become more aware of the threat of nonpoint-source contamination. Many relatively small, widespread sources create contamination. Each source by itself may seem insignificant; however, when the sources are added together they can pose a serious threat.

Hundreds of thousands of homes in Washington State have gardens. Each garden may contribute a relatively small amount of runoff containing soil, chemicals, and fertilizers that flows into our lakes, rivers, and bays (surface water). Nitrates (formed from fertilizers and manures) or certain pesticides that leach through the soil can contaminate groundwater. Added up, the small contributions form a sizable problem. Only when individuals take responsibility and make wise choices can we control nonpoint contamination.

Good gardens thrive with good water quality practices. The same simple, practical techniques that improve soil, beautify the landscape, reduce maintenance, and enhance plant health can also protect the quality of our water.

As a gardener, use these keys to protecting water quality:

An environmentally-sound garden begins with proper planning and design. Properly selected plants and landscape features can reduce runoff and minimize pesticide and fertilizer use in your garden. For example, pavement and gravel allow much greater runoff than a landscape of trees or grass (Table 1). Maintenance of a perfect lawn often involves more reliance on chemicals than other types of landscapes.

Soil is the essential foundation of a garden. Proper soil and fertility management will produce a healthier landscape and reduce the potential for water contamination from erosion, fertilizers, and pesticides.

Drainage refers to the ability of soil to transmit water through the surface and subsoil. Most landscape plants, fruit trees, and berry bushes require good soil drainage to a depth of at least 2 feet. Drainage also affects the potential for water contamination. A coarse-textured mineral soil, such as sand, will drain rapidly, but it also allows dissolved chemicals to leach into the groundwater. Clay particles that bind these chemicals slow their movement through the soil, reducing the likelihood of groundwater contamination. But a dense clay soil drains slowly, increasing surface runoff.

Fertility refers to the presence of minerals necessary for plant life. Unfortunately, the fertility of garden soils is often less than ideal for plant growth. Gardeners usually compensate by adding fertilizers, either from synthetic or natural sources. Overapplication of any fertilizer or manure can result in water carrying excess nutrients into lakes and streams or leaching them into groundwater.

Overfertilization also wastes money, damages plants, and can encourage weeds.

Conditioning can greatly enhance the productivity of soil. Incorporating organic matter, such as compost, ground bark, or sawdust increases the soil's ability to store moisture and nutrients. In addition, adding organic matter can buffer the effects of pesticides in the soil and prevent the rapid leaching of many chemicals into groundwater.

Beating rain and moving water can carry away soil particles, organic matter, plant nutrients, and soil contaminants. This water-soil-chemical mix can cloud natural waters, stimulate unnatural and ecologically disastrous algal blooms, and contaminate fish. Therefore, it is essential to minimize erosion and runoff.

Overwatering can wash away soil, pesticides, and nutrients, which eventually find their way into surface water or groundwater. Overwatering occurs when water is applied faster than the ground can absorb it, or when you let the water run too long. By watering efficiently, you will reduce your water bill while protecting water quality.

Hand watering, either with a hose or a watering can, is generally appropriate for containers or small beds only. Hand watering lawns and planting beds usually does no more than wet the soil surface. Sprinklers can generate considerable runoff if they apply water too fast or throw water onto paved surfaces. Soaker hoses reduce runoff and evaporative losses because they apply water slowly. Trickle or drip irrigation is also efficient, reducing water use by 50% to 80% compared with overhead irrigation.

Do not water according to the calendar, since a plant's water requirement will vary depending on weather, soil, plant species, and age or size of the plant. Never allow seedlings to dry out. Newly established plants will need frequent watering until their root systems become well established. Established trees and shrubs usually do well if you soak them once or twice a month during the summer. Many drought-resistant plants require little or no watering (at least in western Washington) once they are established.

A lawn west of the Cascades will use about an inch of water per week during hot, dry weather. Apply no more than 1/2 inch of water per hour, but adjust this amount according to soil type. Use small cans to measure the amount of water your sprinklers apply. Turn off the water at the first sign of soil saturation or runoff.

Watch for signs that indicate your lawn needs watering: gray-green color, turf does not spring back after being walked on, and blades of grass roll lengthwise. Lawns generally need irrigation at least once a week in summer to stay green. They can be allowed to go dormant.

The goals of environmentally sound irrigation are to maximize water infiltration and minimize runoff. Reduce the potential for runoff by reducing the need for supplemental irrigation.

A pest-free garden is expensive, impractical, and environmentally undesirable. Attempts to maintain a pest-free garden often result in heavy use of pesticides, which in turn increase the potential for water contamination. Try to keep pest populations below the level at which they cause unacceptable damage. Allowing low levels of pests to survive will help maintain a population of their natural enemies.

The first step to effective pest management is to inspect your plants often so you can catch problems when control measures are most effective, before problems become serious. If you detect and deal with insect and disease problems early, you can reduce or eliminate the need for pesticides.

The object is to make your garden a healthy place for your plants and an inhospitable place for pests.

 For more information, the following publications are available from WSU Cooperative Extension.

EB1721 Defining Water Quality

EB1034 Fertilizing Landscape Trees and Shrubs

EB0422 Home Gardens

EB0482 Home Lawns

EB1722 How Fertilizers and Plant Nutrients Affect Groundwater Quality

EB1123 How Much Fertilizer Should I Use?: Conversion Guide for Home Gardeners

WY/IRP4 Landscaping Kit

EB1579 Landscape Plants for the Inland Northwest

EB0648 Organic Gardening

EB1468 Read Pesticide Labels

EB1633 Role of Soil in Groundwater Protection

EB1386 Safe Disposal of Home Use Pesticides

EB0684 Saving Water: Lawns and Other Turf

EB1640 Growing Small Fruits for the Home Garden

EB1102 Soil Management in Yards and Gardens

EM4834 Water Conservation in Gardens and Landscapes

EB1090 Watering Home Gardens and Landscape Plants

EB1622 Washington Groundwater: A Vital Resource

EB1632 Why the Concern about Agricultural Contamination in Groundwater?

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