Tips From The Water Witch

Irrigation FAQ

  • What is the most effective irrigation system?
    • A set of human eyes and a garden hose in predawn hours or a monitored automated irrigated system.
  • How Long Do I Water ?
    • Depends on what you are growing.To The Point Of Lushness, Not Excessive Growth. For a lawn, Enough Water To Produce About A ¼ Of Inch Growth A Week On A Blade Of Grass. Plant Exposure and Time of year will come into play as well as how cool the nights are. When growing edibles, over watering may produce more quantity, but poorer quality. Soil retention quality and fertilization will impact run times.
  • When Do I Water?
    • More Often When It Is Hot, Less When It Is Not. Early morning watering is best, several hours before sunrise. There is less wind which allows for more water to be applied to landscape area and absorption to occur before water is evaporated with the warmth of the sun. Applying with multiple start times on Irrigation timer will increase penetration and absorption and decrease runoff. Avoid evening watering.
  • What is the main failure of most irrigation system ?
    • Poor human oversight and lack of ongoing management
  • Are weather stations efficient in saving water ?
    • Unmonitored they are a more efficient way of wasting water consistently and faster. For a well monitored system on site weather stations can provide the tools to adjust additional water needed in high evaporation situations, and respond quickly to local patterns to avoid over watering.
    • Schedule Your Own
  • Is it a good idea to rip out my lawn and plant low water use or drought tolerant plants?
    • A well maintained monitored trained established lawn can have 6 to 8 inches to several feet of established root zone and will require less water than new planting. Over seeding with a drought tolerant lawn seed (fesques) blend in late fall and early spring lawn will help maintain long term health.Annually aerating will help an established lawn thrive.
  • What is the simplest way to keep lawns healthy ?
    • Weekly mowing with Water management to control growth to a ¼ inch a week and leave grass cuttings, allows the natural process of green waste to break down and contribute to soil health. Checking sprinkler performance for coverage and that sprinkler heads are flush with grade and perpendicular will help keep system efficient.
  • What does dirt have to do with Irrigation?
    • It does not matter how much you water or efficient you irrigate if you do not take into account the water retention properties of the soil or growing medium. Consistent top dressing with amendment and mulch is aesthetically pleasing but ultimately provides more organic matter to retain water.


What is Evaporation Transpiration ET ?

ET or evaporation transpiration rate is the amount of water loss experienced by plants. The ET Rate is the amount of water needed to be replaced. Each plant or crop is assigned a percent (K Factor) of that rate based on plant needs.


ETMinThe daily evaporation is measure in Inches, sprinkler run times are in minutes determine by their precipitation rate(PR). The chart shows the run times for various sprinkler outputs when the ET Rate is 1 inch for the week. Based on the K Factor you would have to irrigate a lawn ( 60% of ET ) 24 minutes for fixed heads, 72 minutes weekly for rotor sprinklers. Assuming the precipitation rate for fixed heads is (1.50PR) and rotors (.50PR)


Fixed Head SprinklerFixed heads have a large range of precipitation rates up to about 1.5 or 1.7PR. The distance sprinklers throw will impact volume. As a general rule do not exceed 6 minutes on run time to avoid soil saturation and run off, on fixed head sprinklers

A rotor or impact puts out approximately.05 inches precipitation (.50PR) in a hour, Rotor Sprinkler Head it usually has a fine stream and rotates.


ET Charts For 47' North Zone 14-16  San Francisco Bay Area

The information on this page is a guideline for drought prone landscapes, similar to the San Francisco North Bay Area, which traditionally has long stretches of drought, compounded by several years of heavy rains and flooding, then repeats the pattern every decade or so.

Managing the upper canopy of the landscapes dictates the growing pattern and the best investment property owners can make in their landscape is having a licensed arborist come out every two years for trees over 15 to 18 feet.

Keeping trees healthy and shaped helps shrubs and ground cover thrive, controlling and minimizing the canopy will keep the root growth in check and help minimize stress in drought.

Rotor Run Time Based on Evapo Transpiration


Plant selection is sometimes dictated by choice, other times chance of survival. The ideal tree for beauty, function and enjoyment is sometimes planted with the intent of it being trained to fit the location.

The legginess of tree canopies can be from surviving drought, or competing for sun as landscapes mature. End of summer or Fall Equinox pruning is a way of communicating with tree roots to let them know what size specimen they are supporting. Scaling back canopies is a way of removing air condition and shade from the roots, signaling to the plant there is less to support.

Plant life focuses on root growth during the winter months, providing top dressing (amendment, and top soil if needed), aeration from blending and mulch for water retention and helps improve the habitat

Weekly Bay Area Et Watering Updates

Gas powered garden tools emit 5% of the nation's air pollution.

The average homeowner spends 40 hours/year, the equivalent to one-week vacation, mowing the lawn.

30% to 60% of urban freshwater is used for watering lawns (depending on locale).

A 1,000 square foot lawn requires 10,000 gallons of water per summer to maintain a "Green" look. (US. News and World Report, 10/28/96)

80,090,000 pounds of synthetic pesticides are used on US. Lawns each year.

When pesticides are regularly applied, 60-90% of earthworms are killed. Earthworms are invaluable for soil health. (PA Department of Agriculture)

Over 100 million tons of fertilizers are applied to residential lawns and gardens annually. (Audubon)

Redesigning the American Lawn by Herber Bormann. Diana Salmon, Garden Geballe, Yale University Press, 1993.

A drought tolerant established,organically maintained lawn can defy these facts

Effectively Managing Irrigation to produce a ¼ inch of growth a per week, allows the clipping to be used as future feeding for the lawn and eliminate green waste.