Agriculture Reference
In-Depth Information
Providing the Right Amount of Water
Of course, we definitely want to save water. It's absurd how much water goes into our
gardens — especially our lawns. That's why I think about collecting and storing rainwater
before I think about irrigation. Most of us will need to irrigate, especially when we're es-
tablishing new gardens or growing food. We can use captured rainwater for a lot of this.
I recommend irrigating with anything that provides water to the entire landscape: by
hand, with a sprinkler, microspray heads, or even soaker hoses if they overlap enough, al-
though the latter really only have occasional usefulness. I wouldn't worry too much about
evaporation with overhead watering, as research from the University of Nebraska shows
this to be a less than 4% loss. Some gardeners don't like to apply water to the leaves be-
cause the conventional wisdom is that it promotes some disease. It does make sense to
avoid watering at night for this reason, as night time conditions are better for many disease
organisms, but we have also seen the true cause of disease is more a function of a lack of
plant health.
I like to apply water from a sprinkler that gets the leaves wet because that's how it hap-
pens in nature when it rains. I do this in the morning. If I'm using chlorinated city water,
however, I may apply it more to the soil to avoid killing microbes on the leaves. Of course,
the microbes on the soil surface won't be too happy, but we work with what we have, right?
It's difficult to determine exactly how much water to apply. People have developed
mathematical equations and charts and calculators to help with this, and while these tools
are helpful, it's hard to find accurate parameters that you need to feed into these calcula-
tions. For example, how deep do your plant roots go? This is especially difficult to figure
out when we're growing many different kinds of plants. How much water does your sprink-
ler apply per minute? What is the evapotranspiration of your area?
You can find these things out and it's important to do so in a landscape where you're
designing an automated irrigation system that has to work without you being there, but for
home and market gardeners who can pay more attention to our gardens, I prefer to go by
feel. You want to water deeply to encourage the roots to go down, and then allow some
time for the soil to partially dry out, but not entirely. It should be thoroughly wet after you
water it, but not to the point of run off. Even though you should water more deeply and less
often, your mulch layer should generally stay good and moist.
A slope may need to be watered in stages, such as 10 minutes on and 10 minutes off for
an hour, in order to allow time for the water to infiltrate rather than run off. Sandy soils
can't hold as much water, so they need to be watered more often throughout the week with
less water. Silt and clay soils are watered less often with more water, although if they have
low infiltration, they may need to be watered in stages like a sloped garden.
