Determining the best irrigation schedule
for a mixture of landscape plants is difficult enough but when salinity is
involved, either in the soil or in the irrigation water, it complicates
matters. Let’s cover some irrigation do’s and don’ts and see how salinity might
affect the way we irrigate.
for a mixture of landscape plants is difficult enough but when salinity is
involved, either in the soil or in the irrigation water, it complicates
matters. Let’s cover some irrigation do’s and don’ts and see how salinity might
affect the way we irrigate.
Avoid Daily Irrigations
Except for shallow rooted plants like
lawns, annual flowers and vegetables in raised beds, daily irrigations should
be avoided any time of the year. Many turfgrasses and annuals have root systems
that extend into the soil 12 inches or less. During the heat of the summer and
under desert conditions some of these plants may require daily irrigations.
lawns, annual flowers and vegetables in raised beds, daily irrigations should
be avoided any time of the year. Many turfgrasses and annuals have root systems
that extend into the soil 12 inches or less. During the heat of the summer and
under desert conditions some of these plants may require daily irrigations.
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| The deeper you should water. Lawns, annual flowers and annual vegetables have the shallowest roots and need to be watered the most often. |
The concept of irrigating nondesert
landscape plants is focused on wetting the root system to its entire depth,
allowing the soil to drain and re-wetting the soil again when half of this
water has been used by the plant or evaporated.
landscape plants is focused on wetting the root system to its entire depth,
allowing the soil to drain and re-wetting the soil again when half of this
water has been used by the plant or evaporated.
The Amount of Water Applied Varies with the Size of the Plant
So we can see that the volume of water
applied in a single application is directly related to the depth of the root
systems of plants. When designing a landscape irrigation system we try, to the
best of our abilities, to put plants with similar rooting depths on the same
valve or station.
applied in a single application is directly related to the depth of the root
systems of plants. When designing a landscape irrigation system we try, to the
best of our abilities, to put plants with similar rooting depths on the same
valve or station.
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| Create irrigation zones in your landscape that reflect the needs of the plants in it. This is because the only way to water less or more often is to turn the valve to that irrigation line on or off. This is done with the valves. So each valve should represent different irrigation depths in your landscape; trees and large shrubs, smaller and medium size shrubs and small plants. Other valves could include annual plants and lawn and desert adapted plants which don’t need to be watered as often. You could even create another zone just for cacti. (This diagram originally appeared in Sunset magazine many years ago demonstrating Hydra zoning or mini oasis landscaping) |
More often than not we are handed an
irrigation system with a mixture of plants that have a variety of rooting
depths. When deciding an irrigation schedule for a single valve or station we
generally have two options; set the number of minutes based on the average rooting depth of all the plants
or let the plants with deepest root systems dictate the number of minutes of
station runtime.
irrigation system with a mixture of plants that have a variety of rooting
depths. When deciding an irrigation schedule for a single valve or station we
generally have two options; set the number of minutes based on the average rooting depth of all the plants
or let the plants with deepest root systems dictate the number of minutes of
station runtime.
Do We Conserve Water or Minimize Plant Problems?
This decision depends on whether to
conserve water or minimize landscape problems. When we decide to under irrigate
some plants so the majority receive the correct amount of water, we may see
some plant damage. If the under irrigation is not severe, we may see the
slowing of plant growth, a decline in density due to leaf drop, leaf tip or
burning of leaf margins. When plants are severely under irrigated then we begin
to see branch die back and in some cases death.
conserve water or minimize landscape problems. When we decide to under irrigate
some plants so the majority receive the correct amount of water, we may see
some plant damage. If the under irrigation is not severe, we may see the
slowing of plant growth, a decline in density due to leaf drop, leaf tip or
burning of leaf margins. When plants are severely under irrigated then we begin
to see branch die back and in some cases death.
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| This is a mixture of a mulberry tree with cactus growing underneath it. Water the mulberry tree and the cactus gets over irrigated. Water only for the cactus, as this was done, and the mulberry doesn’t get enough water. |
Under irrigating, or applying less water
than dictated by a plants rooting depth, can also impact safety issues. What
happens if we under-irrigate large trees such as pines which have shallow roots
to take up water but require deeper roots to anchor it in the soil?
than dictated by a plants rooting depth, can also impact safety issues. What
happens if we under-irrigate large trees such as pines which have shallow roots
to take up water but require deeper roots to anchor it in the soil?
Current irrigation technology is based
upon time management and varying how water is applied to plants. This
technology varies the amount of water applied to plants by changing the number
of minutes valves are open, increasing or decreasing the points of water
emission or changing the rate of water applied at the point of emission. This
translates to increasing or decreasing the number of drip emitters, bubblers,
nozzles or spray heads or substituting old points of emission for new ones that
have different rates of application.
upon time management and varying how water is applied to plants. This
technology varies the amount of water applied to plants by changing the number
of minutes valves are open, increasing or decreasing the points of water
emission or changing the rate of water applied at the point of emission. This
translates to increasing or decreasing the number of drip emitters, bubblers,
nozzles or spray heads or substituting old points of emission for new ones that
have different rates of application.
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| This is a highly sophisticated Hunter ACC irrigation clock. These types of irrigation clocks are expensive but give you a tremendous amount of flexibility. They wouldn’t be good for small landscapes but an excellent choice for large landscapes that have a lot of irrigation variability. |
Making these changes to an irrigation
system that was designed by a professional and focused on the uniform application
of water, more than likely will make the system less uniform and less efficient.
This will likely result in substantially higher water usage. These types
of alterations to professionally designed systems must be done with care.
system that was designed by a professional and focused on the uniform application
of water, more than likely will make the system less uniform and less efficient.
This will likely result in substantially higher water usage. These types
of alterations to professionally designed systems must be done with care.
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| These six station inexpensive irrigation controllers are fine for most small landscapes that don’t require a lot of flexibility. |
When to Make Changes in the Irrigation System?
There are some obvious cases where changes
must be made. For example, changes must be made when some plants are receiving
excessive amounts of water or not enough water while others on the same valve
appear to be watered adequately.
must be made. For example, changes must be made when some plants are receiving
excessive amounts of water or not enough water while others on the same valve
appear to be watered adequately.
As plants get bigger, they need more
water. When plants get bigger, their tops get bigger as well as their root
system. Increasing plant size requires the application of higher volumes of water.
Increased plant size dictates that the area irrigated under the plant also
needs to be increased. Logic tells us we need to increase the amount of water
by applying it to a larger area.
water. When plants get bigger, their tops get bigger as well as their root
system. Increasing plant size requires the application of higher volumes of water.
Increased plant size dictates that the area irrigated under the plant also
needs to be increased. Logic tells us we need to increase the amount of water
by applying it to a larger area.
Just because a few plants on an irrigation
valve have grown larger seldom requires increasing the number of minutes of
runtime. Other plants on the same circuit that received adequate amounts of
water would then be over-irrigated for the sake of a few.
valve have grown larger seldom requires increasing the number of minutes of
runtime. Other plants on the same circuit that received adequate amounts of
water would then be over-irrigated for the sake of a few.
Is Increasing the Number of Minutes the Right Decision?
Of course increasing the number of minutes
is the easiest solution to the problem but is it the right one? The quick fix
of bumping up the number of minutes creates no new revenue for the landscape
maintenance company and is likely a poor solution to an irrigation problem. Is
it possible that a discussion of the problem with the owner or supervisor might
result in a better solution to the problem for everyone involved? Might this
discussion generate revenue, or even a better looking landscape, and also result
in water conservation?
is the easiest solution to the problem but is it the right one? The quick fix
of bumping up the number of minutes creates no new revenue for the landscape
maintenance company and is likely a poor solution to an irrigation problem. Is
it possible that a discussion of the problem with the owner or supervisor might
result in a better solution to the problem for everyone involved? Might this
discussion generate revenue, or even a better looking landscape, and also result
in water conservation?
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| This is a very pretty valve box and it doesn’t look like 99% of the irrigation valve installations out there. But not jamming too many valves in a box and giving them enough space so that they can be replaced when needed sure helps on an irrigation job. |
The second decision in scheduling
irrigations is determining when to apply water. This is a very different
question than determining how much water to apply. Unlike the first question,
the answer to the second question is implemented solely by determining when to
turn the valve on or off.
irrigations is determining when to apply water. This is a very different
question than determining how much water to apply. Unlike the first question,
the answer to the second question is implemented solely by determining when to
turn the valve on or off.
No Technology Replaces a Good Irrigation Manager
Research has demonstrated that no
irrigation controller, no matter how “smart” it is, can substitute for a
knowledgeable irrigation manager. The principal reason is that knowledgeable
irrigation managers focus on their irrigation schedules ahead of the irrigation curve, not behind it. Most “smart”
irrigation controllers are irrigating behind the irrigation curve or relying on
historical information to predict the future.
irrigation controller, no matter how “smart” it is, can substitute for a
knowledgeable irrigation manager. The principal reason is that knowledgeable
irrigation managers focus on their irrigation schedules ahead of the irrigation curve, not behind it. Most “smart”
irrigation controllers are irrigating behind the irrigation curve or relying on
historical information to predict the future.
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| Weather stations like this one help irrigation managers to determine how much water was lost from the landscape. They can run a couple of thousand dollars but for large irrigated areas, they save money in the long run. However, research has demonstrated nothing replaces a good irrigation manager. A good irrigation manager will take this information and fine-tune it and save even more water. |
Knowing when to turn an irrigation valve
on is half art and half science. The “science” part of it can be handled by
many good irrigation controllers. The “art” part of it is staying aware of your
irrigation system, how it’s operating, monitoring the landscape and paying
close attention to current as well as projected future weather conditions,
particularly during the summer months.
on is half art and half science. The “science” part of it can be handled by
many good irrigation controllers. The “art” part of it is staying aware of your
irrigation system, how it’s operating, monitoring the landscape and paying
close attention to current as well as projected future weather conditions,
particularly during the summer months.
You can’t do a good job irrigating sitting
behind a desk. Knowledgeable irrigation managers seldom if ever take vacations
during the heat of the summer. That is their busiest time. This is the time
they are most aware of their landscape environment, weather environment and
irrigation “system” environment.
behind a desk. Knowledgeable irrigation managers seldom if ever take vacations
during the heat of the summer. That is their busiest time. This is the time
they are most aware of their landscape environment, weather environment and
irrigation “system” environment.
Monitor Three Weather Conditions
Three primary weather factors good
irrigation managers are constantly monitoring, whether they realize it or not, current
or potential changes in the temperature, wind and sunlight intensity.
irrigation managers are constantly monitoring, whether they realize it or not, current
or potential changes in the temperature, wind and sunlight intensity.
In most environments, and in particular
desert environments, our everyday irrigation predictions are based on normal,
seasonal temperatures, normal wind speed and a clear sky. The single factor
most likely create mayhem in a landscape during the summer months is wind. The
second is above normal spikes in temperature. The absolute worst scenario is a
spike in daytime temperature accompanied with strong winds and a clear sky. A
good irrigation manager stays ahead of the curve by applying water in
anticipation of mayhem, not during mayhem.
desert environments, our everyday irrigation predictions are based on normal,
seasonal temperatures, normal wind speed and a clear sky. The single factor
most likely create mayhem in a landscape during the summer months is wind. The
second is above normal spikes in temperature. The absolute worst scenario is a
spike in daytime temperature accompanied with strong winds and a clear sky. A
good irrigation manager stays ahead of the curve by applying water in
anticipation of mayhem, not during mayhem.
Salts Complicate Things
As if this was not difficult enough, salts
and salinity add a dimension to the irrigation dilemma which test the abilities
of the best irrigation managers. Salts are salts. Without getting too
technical, any time a substance is added to water and dissolves you have the
potential for increasing salinity. Any time you add something to the irrigation
water or the soil you may affect salinity.
and salinity add a dimension to the irrigation dilemma which test the abilities
of the best irrigation managers. Salts are salts. Without getting too
technical, any time a substance is added to water and dissolves you have the
potential for increasing salinity. Any time you add something to the irrigation
water or the soil you may affect salinity.
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| Saltz, particularly those that contain sulfates, are corrosive to cement and steel. |
Two types of plant damage result from
excess salts or salinity in the soil or irrigation water; the type of salt may be
directly toxic to the plant (such is the case with plain old table salt which
contains two very toxic chemicals to plants; sodium and chlorine or chlorides)
and competition with the plant for water.
excess salts or salinity in the soil or irrigation water; the type of salt may be
directly toxic to the plant (such is the case with plain old table salt which
contains two very toxic chemicals to plants; sodium and chlorine or chlorides)
and competition with the plant for water.
Any type of salt, table salt or even
fertilizers, will dissolve in water adding to a general increase in salinity. Slow
release fertilizers are less of a problem in this regard than fast or quick
release fertilizers. When salts of any kind are added to the soil, these salts
compete with the plant for soil moisture.
fertilizers, will dissolve in water adding to a general increase in salinity. Slow
release fertilizers are less of a problem in this regard than fast or quick
release fertilizers. When salts of any kind are added to the soil, these salts
compete with the plant for soil moisture.
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| Salts can leave behind deposits on drip emitters. |
In other words the salinity of the soil
“pulls” or holds on to water, making water less available to the plant. This
means that when salinity is a problem, we need to irrigate more frequently to
reduce plant stress. This is particularly true in summer months.
“pulls” or holds on to water, making water less available to the plant. This
means that when salinity is a problem, we need to irrigate more frequently to
reduce plant stress. This is particularly true in summer months.
Two basic concepts
when irrigating to avoid salinity problems are dilution and flushing.
Keep the salts diluted and add enough water to flush these salts below the rootzone.
This requires that the soil drains adequately.