Documents of Interest:
- Soil + Mulch
- Planning + Planting
- Watering Wisely
- Think Twice Before Using Pestisides
- Natural Lawn Care
In the summer, when the Puget Sound area receives little rain, the demand on our water system almost doubles from winter – mostly because so much water is used on landscapes. The Environmental Protection Agency estimates that 50% or more of irrigation water is wasted due to evaporation, wind, runoff, or overwatering.
Prepare Your Garden for Watering Wisely
Know – and improve – your soil: The type of soil you have (sandy, loamy, or clay) influences how fast it can absorb water, how often plants need to be watered, and how much water you need to apply. To save water and improve the health of plants, you want soil that absorbs water easily, holds water for plants longer, and drains well. Soil that is low in organic matter can be improved by mixing in compost or other organic matter when you plant.
Group plants with similar water needs: Some plants do not need to be watered after the first few years, while others will always need to be watered regularly. Grouping plants makes it easier to give them only the amount of water they need and no more.
Plant native, adapted, and drought-tolerant plants which do not need to be watered once they are established (generally 2 to 3 years).
Plan the amount of grass in your yard: In a conventional yard, grass is often one of the highest water and chemical users. Decide how much grass you really need and consider replacing other lawn areas with native/adapted plants such as groundcovers or shrubs, or mulch.
Add mulch to planting beds to help soil hold water.
Aerate your lawn and remove thatch to improve water infiltration and irrigation efficiency.
How to Water Efficiently
Water deeply and infrequently to wet all of a plant’s roots. Shallow watering encourages shallow roots, which make plants more vulnerable to drought and damage. Allowing the top few inches of soil to dry out between waterings lets plant roots and soil organisms breathe and encourages roots to grow, seeking deeper moisture. To find out whether you have watered deeply enough or need to water at all, check soil moisture by digging in with a spade or a soil probe, or using a soil moisture sensor.
Avoid runoff by checking to make sure you are not applying water faster than soil can accept it. Look for water pooling on the surface of the ground or running down the gutter when you water. If this occurs, “cycle” your sprinklers: turn them off, wait a few hours, then finish watering.
Adjust sprinkler position to apply water only on target areas. Keep sprinklers from watering the pavement.
Use a water timer that screws onto a faucet and can turn water off after a set period of time.
Water plants in early morning or late evening to reduce water loss to evaporation and wind.
Overwatering drowns plants: they cannot get the oxygen they need, roots can rot, and they have more difficulty absorbing nutrients.
When to Water
Adjust watering schedules with the weather and cool seasons. Plants use more water during hot, dry weather. Established plants only need about half as much water in May and September as they do in July. If you use the same watering schedule from May through September, you are probably overwatering in spring and fall. Cloudy, cool, or rainy weather lowers water need even more.
To avoid overwatering:
- Use a rain gauge to check how much rain has fallen, check soil moisture, and look for signs that plants need water.
- Decrease the amount you water by the amount it has rained.
- Use the guide at www.iwms.org/seattle_area.asp to find out how to adjust watering using the local evapotranspiration rate (a measure of how much water plants use).
- Wait until the top 1 to 2 inches of soil is dry before watering.
- Don’t water when it’s raining.
How Much to Water
Annuals and vegetables: Check soil often to ensure it stays moist 1 to 2 inches below the surface (transplants and seedlings need more water). In general, soil is moist if you can roll it into a ball in the palm of your hand.
Perennials: Many native and adapted species do not usually need to be watered after they are established (2 to 3 years). For others, check gardening books or ask nursery experts.
Trees and shrubs: Established trees and shrubs usually do not need to be watered unless it is very dry. Trees obtain water best when it soaks in around the dripline to a depth of 12 inches. During warm weather, a tree needs 10 gallons of water per inch of the tree’s diameter every 1 to 2 weeks (a 2-inch diameter tree needs 20 gallons of water). Using mulch instead of grass under trees reduces competition for water.
There are many ways to water a lawn and garden – some wiser than others. Using different systems for watering different types of plants can help plants get the right amount of water while conserving water.
Watering by hand
Watering by hand can be very efficient when done well, but it can also lead to considerable water waste. Here are four ways to water well:
- Soaker hoses apply water directly into the soil, so they are much more efficient than sprinklers. Soaker hoses belong in garden beds and around trees and shrubs, but not the lawn unless there are steep slopes.
- A portable sprinkler attached to a hose can be a good way to water a small lawn. Choose a sprinkler that applies water evenly and has a spray pattern that matches your lawn’s shape to avoid watering the sidewalk.
- Use a timer to avoid forgetting to turn off the sprinkler. Also use a backflow preventer to keep dirty water from contaminating drinking water.
- Buy a good hose that won’t kink or crack, leading to hassles and leaks. A good hose has thicker walls, sometimes using layers of reinforcing fabric such as nylon or rayon. Good hose couplings and swivels are important for stopping leaks.
Automatic irrigation systems
A well-designed and maintained automatic irrigation system can greatly reduce water waste and help plants thrive. Unfortunately, many systems are poorly designed, programmed, and maintained, resulting in wasted water and plants that receive too much or too little water. To get the most out of your automatic system:
- Get to know your irrigation controller. An automatic controller attached to a well-designed irrigation system can do a better job of watering than most people. A controller should have the ability to water landscape areas differently (for example, grass, a vegetable garden, and native plants would be on different schedules). Learn how your controller works and adjust it according to the seasons and weather. Some newer controllers have a percent adjust function that you can use to make these adjustments based on the local evapotranspiration rate. Weather-based controllers make these adjustments for you. Remember, an “automatic” irrigation controller set improperly can waste water “automatically”.
- Install a rain sensor that turns off your system when it rains.
- Install soil moisture sensors to detect the amount of moisture at the level of the root system. This will give a more exact measure of how much water plants receive and need.
- Cover drip systems with mulch to prevent evaporation and spread the water flow.
Drip irrigation systems
Drip/micro-irrigation is one of the most efficient forms of irrigation. By watering plants slowly and applying water close to the root zone, drip irrigation minimizes water loss to evaporation, runoff, and watering areas that do not need it. Micro-irrigation is good for trees, shrubs, planting beds, and vegetable gardens. Micro-irrigation emitters include drip emitters, micro-sprays, and bubblers.
- Emitters “drip” water at a slow rate.
- Bubblers emit higher flows of water in a circular pattern and are useful for larger plants and for filling basins.
- Microsprays emit a gentle spray of water.
Underground sprinkler systems
Lawns can be efficiently watered with a well-designed, installed, and maintained automatic underground sprinkler system. Adjust the spray pattern on automatic sprinkler heads to apply water only to areas that need it. Also, use sprinklers that apply water slowly so the soil can absorb water without runoff.
Sprinkler heads fall into two categories: spray and rotary. Spray heads produce a fixed spray while rotors move as they shoot out a jet of water. Rotors apply water at a slower rate than spray heads, creating less runoff.
Sprinkler heads can emit water across different arcs. To avoid wasting water, choose arcs that are consistent with the shape of the area to be watered. Spray heads can be purchased with a set of adjustable arcs. Rotors are always adjustable.
Use only the necessary sprinklers to achieve head-to-head coverage: spray from one sprinkler should reach the head of the next sprinkler. For full coverage without wasted water, each area should be covered by three sprinklers, but no more.
Maintain your irrigation system
At the beginning of the watering season, inspect your system for leaks and malfunctioning heads. Consider having a professional test and adjust your system annually. Throughout the season, periodically run your system for a short time when you are home and check for leaks in nozzles, hoses or sprinkler heads; clogs; and misdirected sprinklers and emitters.
Look for broken or clogged emitters, feeble output, and wet or dry spots. If the lowest sprinkler leaks constantly, it’s not shutting off completely. Inspect valves and replace worn or damaged parts. If there are other wet spots or eroding soil, this could be a sign of a broken pipe in the lawn; around valves, you could have a loose connection or old, leaky washers.
Water Conservation Program, Tacoma Water: www.tacomawater.com
Partnership for Water Conservation resource library: www.partners4water.org/
US Environmental Protection Agency’s WaterSense program: www.epa.gov/watersense
The Irrigation Association’s Irrigation Consumer Handbook: www.smartirrigationmonth.org