Chapter 7_Gardening without irrigation

The Backyard

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:

Water-Wise Efficiency of Vegetable Crops

(in terms of backyard usage of space and moisture)

EFFICIENT ENOUGH

Early spring-sown crops: peas, broccoli, lettuce, radishes, savoy

cabbage, kohlrabi

Overwintered crops: onions, broccoli cauliflower,

cabbage, favas beans

Endive Kale

Garden sorrel

Indeterminate tomatoes

Giant kohlrabi

Parsley--leaf and root

heirloom summer squash (sprawly)

Pole beans

Herbs: marjoram, thyme, dill, cilantro, fennel, oregano

Root crops: carrots, beets, parsnips

MARGINAL

Brussels sprouts (late)

Potatoes

Determinate tomatoes

Rutabagas

Eggplant

Leeks

Savoy cabbage (late)

Peppers, small fruited

INEFFICIENT

Beans, bush snap

Peppers, bell

Broccoli, summer

Radishes

Cauliflower

Scallions, bulb onions

Celery

Sweet corn

Lettuce

Turnips

Have fun planning your own water-wise garden!