Produced by Steve Solomon. HTML version by Al Haines.
Cascadia Gardening Series
Gardening Without Irrigation: or without much, anyway
Steve Solomon
CONTENTS
Chapter
1 Predictably Rainless Summers
2 Water-Wise Gardening Science
3 Helping Plants to Need Less Irrigation
4 Water-Wise Gardening Year-Round
5 How to Grow It with Less Irrigation: A-Z
6 My Own Garden Plan
7 The Backyard
Introduction
Starting a New Gardening Era
First, you should know why a maritime Northwest raised-bed gardener
named Steve Solomon became worried about his dependence on
irrigation.
I'm from Michigan. I moved to Lorane, Oregon, in April 1978 and
homesteaded on 5 acres in what I thought at the time was a cool,
showery green valley of liquid sunshine and rainbows. I intended to
put in a big garden and grow as much of my own food as possible.
Two months later, in June, just as my garden began needing water, my
so-called 15-gallon-per-minute well began to falter, yielding less
and less with each passing week. By August it delivered about 3
gallons per minute. Fortunately, I wasn't faced with a completely
dry well or one that had shrunk to below 1 gallon per minute, as I
soon discovered many of my neighbors were cursed with. Three gallons
per minute won't supply a fan nozzle or even a common impulse
sprinkler, but I could still sustain my big raised-bed garden by
watering all night, five or six nights a week, with a single, 2-1/2
gallon-per-minute sprinkler that I moved from place to place.
I had repeatedly read that gardening in raised beds was the most
productive vegetable growing method, required the least work, and
was the most water-efficient system ever known. So, without adequate
irrigation, I would have concluded that food self-sufficiency on my
homestead was not possible. In late September of that first year, I
could still run that single sprinkler. What a relief not to have
invested every last cent in land that couldn't feed us.
For many succeeding years at Lorane, I raised lots of organically
grown food on densely planted raised beds, but the realities of
being a country gardener continued to remind me of how tenuous my
irrigation supply actually was. We country folks have to be
self-reliant: I am my own sanitation department, I maintain my own
800-foot-long driveway, the septic system puts me in the sewage
business. A long, long response time to my 911 call means I'm my own
self-defense force. And I'm my own water department.
Without regular and heavy watering during high summer, dense stands
of vegetables become stunted in a matter of days. Pump failure has
brought my raised-bed garden close to that several times. Before my
frantic efforts got the water flowing again, I could feel the
stressed-out garden screaming like a hungry baby.
As I came to understand our climate, I began to wonder about
_complete_ food self-sufficiency. How did the early pioneers
irrigate their vegetables? There probably aren't more than a
thousand homestead sites in the entire maritime Northwest with
gravity water. Hand pumping into hand-carried buckets is impractical
and extremely tedious. Wind-powered pumps are expensive and have
severe limits.
The combination of dependably rainless summers, the realities of
self-sufficient living, and my homestead's poor well turned out to
be an opportunity. For I continued wondering about gardens and
water, and discovered a method for growing a lush, productive
vegetable garden on deep soil with little or no irrigation, in a
climate that reliably provides 8 to 12 virtually dry weeks every
summer.
Gardening with Less Irrigation
Being a garden writer, I was on the receiving end of quite a bit of
local lore. I had heard of someone growing unirrigated carrots on
sandy soil in southern Oregon by sowing early and spacing the roots
1 foot apart in rows 4 feet apart. The carrots were reputed to grow
to enormous sizes, and the overall yield in pounds per square foot
occupied by the crop was not as low as one might think. I read that
Native Americans in the Southwest grew remarkable desert gardens
with little or no water. And that Native South Americans in the
highlands of Peru and Bolivia grow food crops in a land with 8 to 12
inches of rainfall. So I had to wonder what our own pioneers did.
In 1987, we moved 50 miles south, to a much better homestead with
more acreage and an abundant well. Ironically, only then did I grow
my first summertime vegetable without irrigation. Being a low-key
survivalist at heart, I was working at growing my own seeds. The
main danger to attaining good germination is in repeatedly
moistening developing seed. So, in early March 1988, I moved six
winter-surviving savoy cabbage plants far beyond the irrigated soil
of my raised-bed vegetable garden. I transplanted them 4 feet apart
because blooming brassicas make huge sprays of flower stalks. I did
not plan to water these plants at all, since cabbage seed forms
during May and dries down during June as the soil naturally dries
out.
That is just what happened. Except that one plant did something a
little unusual, though not unheard of. Instead of completely going
into bloom and then dying after setting a massive load of seed, this
plant also threw a vegetative bud that grew a whole new cabbage
among the seed stalks.
With increasing excitement I watched this head grow steadily larger
through the hottest and driest summer I had ever experienced.
Realizing I was witnessing revelation, I gave the plant absolutely
no water, though I did hoe out the weeds around it after I cut the
seed stalks. I harvested the unexpected lesson at the end of
September. The cabbage weighed in at 6 or 7 pounds and was sweet and
tender.
Up to that time, all my gardening had been on thoroughly and
uniformly watered raised beds. Now I saw that elbow room might be
the key to gardening with little or no irrigating, so I began
looking for more information about dry gardening and soil/water
physics. In spring 1989, I tilled four widely separated, unirrigated
experimental rows in which I tested an assortment of vegetable
species spaced far apart in the row. Out of curiosity I decided to
use absolutely no water at all, not even to sprinkle the seeds to
get them germinating.
I sowed a bit of kale, savoy cabbage, Purple Sprouting broccoli,
carrots, beets, parsnips, parsley, endive, dry beans, potatoes,
French sorrel, and a couple of field cornstalks. I also tested one
compact bush (determinate) and one sprawling (indeterminate) tomato
plant. Many of these vegetables grew surprisingly well. I ate
unwatered tomatoes July through September; kale, cabbages, parsley,
and root crops fed us during the winter. The Purple Sprouting
broccoli bloomed abundantly the next March.
In terms of quality, all the harvest was acceptable. The root
vegetables were far larger but only a little bit tougher and quite a
bit sweeter than usual. The potatoes yielded less than I'd been used
to and had thicker than usual skin, but also had a better flavor and
kept well through the winter.
The following year I grew two parallel gardens. One, my "insurance
garden," was thoroughly irrigated, guaranteeing we would have plenty
to eat. Another experimental garden of equal size was entirely
unirrigated. There I tested larger plots of species that I hoped
could grow through a rainless summer.
By July, growth on some species had slowed to a crawl and they
looked a little gnarly. Wondering if a hidden cause of what appeared
to be moisture stress might actually be nutrient deficiencies, I
tried spraying liquid fertilizer directly on these gnarly leaves, a
practice called foliar feeding. It helped greatly because, I
reasoned, most fertility is located in the topsoil, and when it gets
dry the plants draw on subsoil moisture, so surface nutrients,
though still present in the dry soil, become unobtainable. That
being so, I reasoned that some of these species might do even better
if they had just a little fertilized water. So I improvised a simple
drip system and metered out 4 or 5 gallons of liquid fertilizer to
some of the plants in late July and four gallons more in August. To
some species, extra fertilized water (what I call "fertigation")
hardly made any difference at all. But unirrigated winter squash
vines, which were small and scraggly and yielded about 15 pounds of
food, grew more lushly when given a few 5-gallon,
fertilizer-fortified assists and yielded 50 pounds. Thirty-five
pounds of squash for 25 extra gallons of water and a bit of extra
nutrition is a pretty good exchange in my book.
The next year I integrated all this new information into just one
garden. Water-loving species like lettuce and celery were grown
through the summer on a large, thoroughly irrigated raised bed. The
rest of the garden was given no irrigation at all or minimally
metered-out fertigations. Some unirrigated crops were foliar fed
weekly.
Everything worked in 1991! And I found still other species that I
could grow surprisingly well on surprisingly small amounts of
water[--]or none at all. So, the next year, 1992, I set up a
sprinkler system to water the intensive raised bed and used the
overspray to support species that grew better with some moisture
supplementation; I continued using my improvised drip system to help
still others, while keeping a large section of the garden entirely
unwatered. And at the end of that summer I wrote this book.
What follows is not mere theory, not something I read about or saw
others do. These techniques are tested and workable. The
next-to-last chapter of this book contains a complete plan of my
1992 garden with explanations and discussion of the reasoning behind
it.
In _Water-Wise Vegetables_ I assume that my readers already are
growing food (probably on raised beds), already know how to adjust
their gardening to this region's climate, and know how to garden
with irrigation. If you don't have this background I suggest you
read my other garden book, _Growing Vegetables West of the
Cascades,_ (Sasquatch Books, 1989).
Steve Solomon
Chapter 1
Predictably Rainless Summers
In the eastern United States, summertime rainfall can support
gardens without irrigation but is just irregular enough to be
worrisome. West of the Cascades we go into the summer growing season
certain we must water regularly.
My own many-times-revised book _Growing Vegetables West of the
Cascades_ correctly emphasized that moisture-stressed vegetables
suffer greatly. Because I had not yet noticed how plant spacing
affects soil moisture loss, in that book I stated a half-truth as
law: Soil moisture loss averages 1-1/2 inches per week during
summer.
This figure is generally true for raised-bed gardens west of the
Cascades, so I recommended adding 1 1/2 inches of water each week
and even more during really hot weather.
Summertime Rainfall West of the Cascades (in inches)*
Location April May June July Aug. Sept. Oct.
Eureka, CA 3.0 2.1 0.7 0.1 0.3 0.7 3.2
Medford, OR 1.0 1.4 0.98 0.3 0.3 0.6 2.1
Eugene, OR 2.3 2.1 1.3 0.3 0.6 1.3 4.0
Portland, OR 2.2 2.1 1.6 0.5 0.8 1.6 3.6
Astoria, OR 4.6 2.7 2.5 1.0 1.5 2.8 6.8
Olympia, WA 3.1 1.9 1.6 0.7 1.2 2.1 5.3
Seattle, WA 2.4 1.7 1.6 0.8 1.0 2.1 4.0
Bellingham, WA 2.3 1.8 1.9 1.0 1.1 2.0 3.7
Vancouver, BC 3.3 2.8 2.5 1.2 1.7 3.6 5.8
Victoria, BC 1.2 1.0 0.9 0.4 0.6 1.5 2.8
*Source: Van der Leeden et al., _The Water Encyclopedia,_ 2nd ed.,
(Chelsea, Mich.: Lewis Publishers, 1990).
Defined scientifically, drought is not lack of rain. It is a dry
soil condition in which plant growth slows or stops and plant
survival may be threatened. The earth loses water when wind blows,
when sun shines, when air temperature is high, and when humidity is
low. Of all these factors, air temperature most affects soil
moisture loss.
Daily Maximum Temperature (F)*
July/August Average
Eureka, CA 61
Medford, OR 89
Eugene, OR 82
Astoria, OR 68
Olympia, WA 78
Seattle, WA 75
Bellingham, WA 74
Vancouver, BC 73
Victoria, BC 68
*Source: The Water Encyclopedia.
The kind of vegetation growing on a particular plot and its density
have even more to do with soil moisture loss than temperature or
humidity or wind speed. And, surprising as it might seem, bare soil
may not lose much moisture at all. I now know it is next to
impossible to anticipate moisture loss from soil without first
specifying the vegetation there. Evaporation from a large body of
water, however, is mainly determined by weather, so reservoir
evaporation measurements serve as a rough gauge of anticipated soil
moisture loss.
Evaporation from Reservoirs (inches per month)*
Location April May June July Aug. Sept. Oct.
Seattle, WA 2.1 2.7 3.4 3.9 3.4 2.6 1.6
Baker, OR 2.5 3.4 4.4 6.9 7.3 4.9 2.9
Sacramento, CA 3.6 5.0 7.1 8.9 8.6 7.1 4.8
*Source: _The Water Encyclopedia_
From May through September during a normal year, a reservoir near
Seattle loses about 16 inches of water by evaporation. The next
chart shows how much water farmers expect to use to support
conventional agriculture in various parts of the West. Comparing
this data for Seattle with the estimates based on reservoir
evaporation shows pretty good agreement. I include data for Umatilla
and Yakima to show that much larger quantities of irrigation water
are needed in really hot, arid places like Baker or Sacramento.
Estimated Irrigation Requirements:
During Entire Growing Season (in inches)*
Location Duration Amount
Umatilla/Yakama Valley April-October 30
Willamette Valley May-September 16
Puget Sound May-September 14
Upper Rogue/Upper Umpqua Valley March-September 18
Lower Rogue/Lower Coquille Valley May-September 11
NW California April-October 17
*Source: _The Water Encyclopedia_
In our region, gardens lose far more water than they get from
rainfall during the summer growing season. At first glance, it seems
impossible to garden without irrigation west of the Cascades. But
there is water already present in the soil when the gardening season
begins. By creatively using and conserving this moisture, some
maritime Northwest gardeners can go through an entire summer without
irrigating very much, and with some crops, irrigating not at all.