Water-Wise Gardener





I am an unusually fortunate gardener. After seven years of
struggling on one of the poorest growing sites in this region we now
live on 16 acres of mostly excellent, deep soil, on the floor of a
beautiful, coastal Oregon valley. My house and gardens are perched
safely above the 100-year flood line, there's a big, reliable well,
and if I ever want more than 20 gallons per minute in midsummer,
there's the virtually unlimited Umpqua River to draw from. Much like
a master skeet shooter who uses a .410 to make the sport more
interesting, I have chosen to dry garden.
Few are this lucky. These days the majority of North Americans live
an urban struggle. Their houses are as often perched on steep,
thinly soiled hills or gooey, difficult clay as on a tiny fragment
of what was once prime farmland. And never does the municipal
gardener have one vital liberty I do: to choose which one-sixth of
an acre in his 14-acre "back yard" he'll garden on this year.
I was a suburban backyard gardener for five years before deciding to
homestead. I've frequently recalled this experience while learning
to dry garden. What follows in this chapter are some strategies to
guide the urban in becoming more water-wise.
Water Conservation Is the Most Important First Step
After it rains or after sprinkler irrigation, water evaporates from
the surface until a desiccated earth mulch develops. Frequent light
watering increases this type of loss. Where lettuce, radishes, and
other shallow-rooting vegetables are growing, perhaps it is best to
accept this loss or spread a thin mulch to reduce it. But most
vegetables can feed deeper, so if wetting the surface can be
avoided, a lot of water can be saved. Even sprinkling longer and
less frequently helps accomplish that. Half the reason that drip
systems are more efficient is that the surface isn't dampened and
virtually all water goes deep into the earth. The other half is that
they avoiding evaporation that occurs while water sprays through the
air between the nozzle and the soil. Sprinkling at night or early in
the morning, when there is little or no wind, prevents almost all of
this type of loss.
To use drip irrigation it is not necessary to invest in pipes,
emitters, filters, pressure regulators, and so forth. I've already
explained how recycled plastic buckets or other large containers can
be improvised into very effective drip emitters. Besides, drip tube
systems are not trouble free: having the beds covered with fragile
pipes makes hoeing dicey, while every emitter must be periodically
checked against blockage.
When using any type of drip system it is especially important to
relate the amount of water applied to the depth of the soil to the
crops, root development. There's no sense adding more water than the
earth can hold. Calculating the optimum amount of water to apply
from a drip system requires applying substantial, practical
intelligence to evaluating the following factors: soil water-holding
capacity and accessible depth; how deep the root systems have
developed; how broadly the water spreads out below each emitter
(dispersion); rate of loss due to transpiration. All but one of
these factors--dispersion--are adequately discussed elsewhere in
_Gardening Without Irrigation._
A drip emitter on sandy soil moistens the earth nearly straight down
with little lateral dispersion; 1 foot below the surface the wet
area might only be 1 foot in diameter. Conversely, when you drip
moisture into a clay soil, though the surface may seem dry, 18
inches away from the emitter and just 3 inches down the earth may
become saturated with water, while a few inches deeper, significant
dispersion may reach out nearly 24 inches. On sandy soil, emitters
on 12-inch centers are hardly close enough together, while on clay,
30-or even 36-inch centers are sufficient.
Another important bit of data to enter into your arithmetic: 1 cubic
foot of water equals about 5 gallons. A 12-inch-diameter circle
equals 0.75 square feet (A = Pi x Radius squared), so 1 cubic foot
of water (5 gallons) dispersed from a single emitter will add
roughly 16 inches of moisture to sandy soil, greatly overwatering a
medium that can hold only an inch or so of available water per foot.
On heavy clay, a single emitter may wet a 4-foot-diameter circle, on
loams, anywhere in between, 5 gallons will cover a 4-foot-diameter
circle about 1 inch deep. So on deep, clay soil, 10 or even 15
gallons per application may be in order. What is the texture of your
soil, its water-holding capacity, and the dispersion of a drip into
it? Probably, it is somewhere in between sand and clay.
I can't specify what is optimum in any particular situation. Each
gardener must consider his own unique factors and make his own
estimation. All I can do is stress again that the essence of
water-wise gardening is water conservation.
Optimizing Space: Planning the Water-Wise Backyard Garden
Intensive gardening is a strategy holding that yield per square foot
is the supreme goal; it succeeds by optimizing as many growth
factors as possible. So a raised bed is loosened very deeply without
concern for the amount of labor, while fertility and moisture are
supplied virtually without limit. Intensive gardening makes sense
when land is very costly and the worth of the food grown is judged
against organic produce at retail--and when water and nutrients are
inexpensive and/or available in unlimited amounts.
When water use is reduced, yield inevitably drops proportionately.
The backyard water-wise gardener, then, must logically ask which
vegetable species will give him enough food or more economic value
with limited space and water. Taking maritime Northwest rainfall
patterns into consideration, here's my best estimation:





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