last updated 22 Aug 2019

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According to the US Environmental Protection Agency (EPA), 50% of water used outdoors is wasted.

EPA Water Sense Guidelines:
(Note: The following guidelines are for the peak watering month.)

How to water (timing, amount, method)
I'm moving from New Jersey, the Garden State, to California. In New Jersey I only had to water during dry spells every couple of years because of frequent rains and the humid climate. It's a different story in California.

Watering depends a host of factors, including things like soil type, sunlight/shade, plant type and regional climate (humidity, wind).
Other factors are:

  • Where is the plant, container or soil?
    Most container plants need watering on a daily basis in hot, dry conditions
  • How well established and what size is the plant, seedling or mature with deep roots.

Two key rules are:

  • Irrigate deeply and infrequently. Plant roots need air as well as water, so let the water soak in so the plants don't drown.
    For lawns and annuals concentrate their roots in the top 6" of soil; for perennials, shrubs and trees, it's the top 12".
    Watering deeply encourages deep roots to make the plant more drought tolerant.
    There are planter boxes which allow you to water from the bottom.
  • Water in the morning. If you do get moisture on the leaves, this gives them time to dry out. It's much more difficult for plant diseases to get a foothold when the foliage is dry.
    Late afternoon is the second best time.
How Much Water Do Vegetables Need? A good general guideline is an inch of water per week, either by rain or watering; in arid climates, it is double that. In hot weather, vegetables need even more water, up to about 1/2 inch per week extra for every 10 degrees that the average temperature is above 60 degrees.
Squash, eggplant, tomatoes, and other crops with large leaves need more than 1 inch a week.

evapotranspiration (ET) is the release of water to the atmosphere either thru evaporation from the soil or leaves where water taken in by the roots and and used for metabolic and physiologic functions is transported to the leaves.

There sensors like the Hunter WSS - Wireless Solar Sync that continually gathers on-site solar and temperature data used in the calculation of evapotranspiration (ET), then determine watering requirements.

Methods - Water Conservation:
Soaker hoses and drip systems save water because there is less evaporation with them.

Trees:  Once every two weeks, two inches of water
Shrubs: Once a week, one inch of water
Perennials: Once a week initially, finger test biweekly
Most say to water weekly for the first year. I put down cardboard for weed control and 3 inches of mulch and after the first 6 weeks only watered every other month and my new plants planted in the beginning of the summer did fine. Most drought tolerant plants do not like wet feet nor the way drip irrigation delivers the water (some trees have root systems that are mostly horizontal, while drip irrigation delivers the water vertically)

A Garden Watering Guide for California Native Plants

Hold off watering if the top few inches of the soil seems moist.

The second fall and winter, observe and water only if the expected rainfall is low. You should not have to water more than once a month.

Most plants are well established by the time they have gone through two summers and two winters with this garden watering guide to establish deep roots. After this period the plants should need no supplemental watering during summer.

The plants will benefit from the dust being washed off their leaves in the dry summer months. So take a hose, walk around your garden and wash off the leaves when they look dusty, about once or twice a month.

___________________ water at least 6 inches deep for lawns and 12 inches deep for shrubs and trees. A ½ inch watering will wet a sandy soil to about 6 inches. 1 inch of water, (a general rule of thumb) will give deep penetration of the soil to a depth of 6 to 8 inches. Water Wisdom Part 2 (LAWN CARE SIMPLIFIED - A Safe and Natural Approach)

____________ Make Watering Easier

Most lawns need 1 to 2 inches of water per week depending on water and soil conditions.

Test the soil 6 inches or more below the surface to make sure it's dry. Turn on your sprinkler, and periodically test the soil 6 inches down until the water has penetrated to that depth. Keep track of how long it took, and use that as the time you need to water.

Watering Tips, When to Water | Gardener's Supply

Lawns and annuals concentrate their roots in the top 6" of soil; for perennials, shrubs and trees, it's the top 12". In heavy soil, it may take hours for water to percolate down 6-12". Use your finger or a shovel to check the progress.

Mulch reduces surface runoff and slows evaporation from the soil.

How To Water Your Lawn

Watering early in the morning will ensure that your lawn dries completely before

If you have automatic sprinklers, check them regularly to be sure you’re getting complete coverage. nightfall. A wet lawn at night, on a regular basis, can lead to fungus and disease problems.

Plant, Shrub & Tree Watering Guidelines | Oakridge Nursery & Landscaping See also:
Automated Irrigation Systems
Watering timers
Evapotranspiration - The Water Cycle, from USGS Water-Science School
How Often Should Tomato Plants Be Watered? | Home Guides | SF Gate
Vegetable Watering table | The Old Farmer's Almanac

Aside: When I googled "How frequently to water" the 3rd hit was "How often do I water marijuana plants? at Grow Weed Easy." Welcome to California.

Watering Timers
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last updated 1 May 2017