How Much Water?
Homeowners
are always asking questions like “How
long should I water?” or
“How many inches should I water?”.
There is no pat answer for this question, of course, due to all the
variables that can affect your water needs throughout the season(s).
However, if you want a ball park figure for watering, turf pros
generally agree that the amount of water a lawn requires (whether
through rain or through your sprinkler) is ¾
- 1 inch per week.
This amount is for lawns that are actively growing and not dormant or in a
slow growth stage.
Determining
your rate of Water Flow
All
homeowners should have an idea of how much water is coming out when
they turn their sprinkler on. Here is how to figure it out:
Set
out a four or more wide mouth containers (such as pots or tuna cans) on the grass,
spaced evenly within the spray pattern of your sprinkler. Then
turn your sprinklers on and run for twenty minutes (or 1/3 of an hour). Then measure the amount of water in each can with a ruler. Figure out the average amount of water per can after taking all the measurements. Then multiply by 3. This
will tell you, once and for all, how many inches of water you get per
hour of sprinkling -assuming
your water pressure doesn't change. If you are having trouble with this, go to http://www.ipm.ucdavis.edu/TOOLS/TURF/MAINTAIN/output.html
By placing the containers in
various spots, you'll also be able to note whether the spray pattern
of the sprinkler is distributing the water evenly and whether you may
need to make some adjustments or do some overlapping when you move
the sprinklers around.
IF you want to water like a pro, you need to actually take a look
at the soil in the root zone (3-5 inches deep for most home lawns) of
the grass occasionally to see if it is moist, dry or over-saturated.
Step on a spade and push it back and you can see where the dry soil
begins and ends. Get to know your yard, your soil type and where the
dry and wet areas are. You need to be aware of conditions that
will affect the moisture content and make adjustments as needed.
Here
are some factors that will influence your water needs:
Amount of
actual rainfall.
Most people are fooled by rains and think they are getting more water
than they really do get. A rain gage is a good, cheap tool to have.
Temperatures.
This is obvious. Higher temperatures mean faster drying conditions.
It may also speed up grass growth for a while, and that will also
increase water absorption by the grass.
Wind.
If you are in a windy location there is going to be a lot of water
loss due to evaporation.
Tree root
competition.
Trees can take an enormous quantity of water out of the ground and
their roots will go right into the lawn area if that is the only
place where it can find water easily. Lawns on the south side of
trees dry out extremely fast. You need to compensate for the tree's
water needs when you water your lawn.
Soil Compaction. All soils, whether sandy, clay-like or beautiful loams, will absorb water less deeply when they are compacted.

Water sits on top of a compacted Clay soil.
Soil
Quality – Clay versus Sandy Soils.
There is a huge difference between the way sandy soils handle water
and the way clays handle water. Here is what you need to know:
Clay soils
are made up of microscopic size rock particles that bond together
somewhat magnetically. There is little to no airspace between these
particles, and water penetrates through very slowly, completely
saturating the soil with very little “free water” left for
plants. They tend to swell up when wet and shrink back when dry,
often forming cracks in the soil and squeezing or tearing roots.
Denser
clay soils can be very hygroscopic
- meaning water
binds to it so tightly that roots cannot absorb it.
This is why clay soils usually need
more water than you would imagine to keep plants from wilting. If
your clay soil feels wet, but your grass or garden plants are
wilting, you probably have a hygroscopic clay soil that is going to
need more water until the soil is improved.
Sandy
soils, on the other hand, have larger, visible rock particles in
them – perhaps 1000 to 2000 times larger than clay particles. Unless extremely compacted, there
is a lot of airspace between sand particles. Water infiltrates sand
quickly and deeply and there is more “free water” available for
grass and plant roots to grab. If you want an analogy in terms of
size and free airspace, think of sandy soil as a barrel of
basketballs and clay soil as a barrel of marbles.
On
a medium textured sandy
soil,
an inch of water can penetrate down to 12 inches, in just 2-3 hours.
On a medium-clay
soil,
an inch of water may only penetrate about 4 inches deep, and it would
take 6 hours or longer to get that deep. Puddling or runoff is a
real problem on clay soils. In terms of drying out, as you may
suspect, sandy soils dry out much faster than clay soils.
Silt is
a very small soil particle between sand and clay size. It has more of
a sand physical appearance, but tends to compact and tighten up more
like clays when it makes up most of a soil.
Loam soils
are a nice mix of sand, clay, silt and organic matter. If not badly compacted they will absorb, hold
onto and release water in a more ideal fashion. Depending on amounts
of each particle, you can have clay loams, sandy loams or silt loams.
Soil types will be discussed more thoroughly in a later section.
What
does this all mean to you?
We
said earlier, the suggested amount of weekly water for lawns is about
¾ - 1 inch of water. Since an inch of water on a sandy soil
goes perhaps 12 inches deep (and your grass roots are only perhaps
3-6 inches deep), it would be better to water a sandy soil lawn 2 to
3 times a week, putting down ½ -1/3 of an inch respectively.
If
you have a nice loamy soil, or clay loam soil, you can put down an
inch at a time, once a week. But, if you have a more hygroscopic and
water-absorbing clay, you may need more water than what we suggest.
And it might be better to break it up into 2-3 waterings a week, just
like with a sandy soil. If you find that the water is puddling or
running off at all, you should break up your watering into a few
stages on the same day. giving it some time to penetrate deeper
between each watering. You can also use our Aerify liquid soil
conditioner or our Aerify PLUS products to
improve water penetration. Spraying the lawn with dish soap before watering
can also help. Increasing soil organic matter, so more humus
is formed, will also result in better soil water management.
Improving soil quality is vital when you have a clay or sandy soil. Finding better soil improvement methods and products has been part of our company's mission for over 30 years. You can read more about our soil improvement products at www.natureslawn.com
As
we have said many times before this, you need to look at the
lawn and soil in front of you. See things for yourself and
don't just follow the “rules”. If you have determined your rate
of water flow (above), you know how many inches of water your lawn
gets per hour. You should then test your water penetration by letting
the soil dry out and then seeing how far water penetrates with ½
to 1 hour of sprinkling. Then you'll have a clearer picture of your
soil density and drainage, and will know how long you actually need
to water to saturate the root zone. Finally, watch for wilting so
you'll know when to water for sure.
To
read an interesting article by David M. Kopec, on how the physical
properties of your soil affect your water needs, go to:
http://turf.arizona.edu/tips1095.html
Stuart Franklin is President of Nature’s
Lawn & Garden, Inc.
(http://www.natureslawn.com)
a lawn fertilizing company and on line Web Store , located in the
Buffalo, NY area. He is also the author of Building
A Healthy Lawn: A Safe and Natural Approach (Storey Publications 1988), available through Amazon.com
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