by Glenn Davis, UCCE Master
Gardener, El Dorado County
February, 2003
Most watering programs make the assumption that you are
watering on level ground; foothill watering, on the other hand, presents the
gardener with some unique challenges. We are not level, and if our watering
methods don’t take that into consideration, our gardens become the victim of
roller coaster watering, drowning or drying up. Foothill gardeners, like any
other gardener, have to consider how much water the plant needs; they also have
to contend with terrain, run-off, and erosion.
Good irrigation provides the moisture plants need to go
through their growing processes; however all of the water a plant needs does not come from the watering methods
of the gardener. A lot of the moisture used by plants is absorbed from the moisture
found in the atmosphere. Soils also play a role, clay soils have very small
particles that tend to bind the moisture to themselves and as a result create
an airless root environment. Sandy soils allow water to quickly move through
the soil; the results are rapid water depletion and too much air space. The
happy medium is the soil in the middle, with lots of organic matter that holds
the water yet provides the air space necessary for root development. In fact,
good irrigation starts with good soil: improve the soil and you can save water and have a healthy garden.
Urban horticulturists
claim more plants are killed by over-watering than by disease or insects. So
how do you know when your plant needs water? Water is lost by most plants on
the underside of the leaves; if the leaves turn down and start to droop the
plant needs water. If your leaves droop in the cool early morning hours then
you should add some water; leaf droop during mid-day heat is normal. Try and
keep in mind that too much water is just as dangerous as too little water; this
is especially true if your garden soil is our good old red clay.
Vegetable gardens do best with frequent light watering, while
mature orchards require deep watering less frequently. Leaf crops require more
water than root crops. Young crops need a moist root zone and mature plants may
need water only once a month or so. Water needs per plant are dictated by many
factors; the plant’s canopy, the soil absorption rate, amount of water in the
atmosphere, the type of plant, and the depth of the root system are just a few
of the factors involved. As an example, a fruit tree with a canopy six feet in
diameter will use about four and one-half gallons of water a day. To provide
the tree with adequate water in good soil you would water the tree every six days
with 30 gallons of water. If the soil is sandy the tree would require the same
amount of water every 4 days and if the soil is clay the same amount every 7
days. A vegetable garden with the same six-foot canopy would use five and
one-half gallons of water per day and in good soil would require 25 gallons of
water every four days. Keep in mind this is just an example; there are a lot of
factors that could alter these figures.
One of the real joys of gardening is standing in the sun and
sprinkling the garden with water. Sprinkling provides the plant with a quick
water fix, but it also encourages shallow root development and since the water
is airborne, a lot is lost to evaporation before it reaches the soil. Water
applied rapidly without containment frequently runs off the soil once the
surface has been saturated.
If you have reached the stage where hand watering and dragging
hoses has become a loathsome chore, you might consider installing a timed drip
system. Drip irrigation systems apply the water directly to the area where it
is needed. The water is applied slowly and percolates into the soil slowly
almost completely eliminating run-off, soil erosion and evaporation. It is
possible to cut your water usage by as much as 50 per-cent if the system is installed
and operated correctly. It does require a little research, and some initial
expense, but it will save water and time. Low pressure drip systems work off of
a small plastic pipe that can be installed underground or laid on top of the
soil; the latter is preferred to prevent cutting or puncturing it underground. Small
graduated emitters are punched into the soft plastic tubing where they are
needed. The system can be hooked to an anti-siphon valve and controlled by a
timer similar to a lawn sprinkler set-up.
A lot a factors influence water management in the foothills. For
more information on this subject or any garden question, contact the El Dorado
County Master Gardeners, 621-5512, Monday through Friday, 9:00 am to noon.