It is not my role to determine the difference in essential and non-essential water uses.  But many residents have landscape investments affecting property value, and those investments can be adversely affected by poor management.  It is within my role to help you learn to manage water wisely for the best health of plants.  While many people seek formulas for gallons or minutes of water, there are no rules that apply universally.  Many factors affect how often plants need to be watered:  soil texture, soil structure, extent and health of roots, amount of foliage, shape of foliage, texture of foliage surface, humidity, wind, temperature, exposure to sun, time of day, proximity to heat retaining structures such as fences or driveways, time of year, and many others.  And most of these are subject to change frequently.  If you think of the soil as a reservoir, the plant as a straw, and the air as a sponge, it may help you understand what is happening.

Some generalities may help:  larger plants need more water than smaller plants; established plants usually have roots in optimal locations for retrieving water; new plantings may need daily attention by gardeners; established perennial plants tend to fare better than new annual plants; and there are exceptions to most of these generalities. 

In general, it is best to water long and infrequently rather than briefly and often.  With new plantings, however, frequent is sometimes necessary also.  If you drag hoses, you can appreciate doing it weekly instead of daily.  Do a good job of watering today, so that you don’t have to do it again tomorrow.  Or do a good job in one place today, and in another place tomorrow. 

When should you apply water?  The best guideline is to observe the plants and water only on an as needed basis.  If you have an automatic irrigation system, put it on manual.  Put an intelligent human in charge of turning it on and off.  Watch plants for signs of water stress – leaf curl, wilting, change in color.  Lawn grasses will take on a blue to gray cast as the blades curl to reduce water loss; that is a good indicator.  Other plants have similar mechanisms that are more or less obvious.  Wilting is not necessarily an emergency issue; it's the plant's way of reducing water loss.  It's your clue to look further since saturated soil can also cause wilting.  One of my colleagues suggests that each of us has a water sensor often called an index finger; use it. 

When you apply water, whether you drag hoses or have a system controller, you have a certain amount of control.  Automatic systems usually allow you to determine long they run.  You can usually include several run times in each zone on the same day – cycled irrigation.  Some systems allow you to also run it for a percentage of the time that is already set.  When water is needed, a good target is to apply 1/2 inch of water.  (That's about 600 gallons over 1,000 square feet.)  In most of our soils, that will assure water reaching 6 to 8 inches deep. 

Sometimes water will not infiltrate as rapidly as we can apply it.  That will mean that you have to run it until water starts to run off or puddle.  Then you will need to wait for about an hour and start that area again.  Continue until you have applied about 1/2 inch.  This use of multiple run times is called cycled irrigation.  Whether it takes 2, 3, or several run times, it’s still one irrigation in multiple cycles.  These cycles should happen within the same day.

You may need to place rain gauges to determine when 1/2 inch has been applied.  Or you can measure it in a can with flat bottom and straight sides such as a tuna can.  Note that the amount will change depending on how far you are from the sprinkler.  For drip systems, you will probably need to probe the soil with a shovel or spade to evaluate how deep your water is penetrating.  If you note how long it takes various stations on your controller to reach the 1/2 inch goal (or 6-8 inches under drip), then you can subsequently use the same amount of time.

Once you have completely watered a lawn, section of vegetable garden, or shrub, you should turn the water off and not run it again until plants need it.  As I suggested above, there are many, many variables determining when that will be.  It may be 5 days or two weeks.  Most established shrubs should not need irrigation on a regular basis.  In fact at my home these plants are not getting any water supplied.  All water is applied by dragging hoses.  We work with plants to get them established, and then they are on their own until we notice a problem.  Under that strategy, plants are forced to forage more extensively with their roots for water.  We haven't trained them to expect a surface application on a regular basis; consequently they don't invest a lot of energy in shallow roots.

For plantings that are new or not well established, we have implemented a poor man’s version of drip irrigation.  3-gallon plant pots are lined with plastic grocery bags and placed beside those plants.  When the plants need to be watered, we fill the bags with water.  Since the bags are not designed to hold water, they slowly leak around the plant.  That allows the water to soak deep around the roots rather than running across the surface.  Plants more than 2 years old are not yet showing signs of stress.

One further word about lawns:  The lawn may look bad if it’s not watered, but it’s not likely to die.  Our lawn at home has never been irrigated beyond rainfall.  Fescue pastures never get irrigated and look pretty brown right now.  But they will green up as soon as they get water.  If your lawn has become accustomed to regular applications of water, you can wean it off.  Start by doubling the time between irrigations.  Most lawns can be kept alive with a good watering about every 3 weeks.  They may not look good, but we may find there are more important uses for our water before summer is over.   

If you’re growing vegetables, water can make a difference in whether you will have a harvest.  Water to the depth of the roots, use ooze hoses to avoid runoff, use mulch to reduce loss.  There’s both art and science to water management.  But it can be managed.  And management is best done by an informed human being.  That’s where you come in.