IRRIGATION
My well has
run dry. When it rains, it pours. Water, water everywhere but not a drop to
drink. A hard rain’s a-gonna fall. If it keeps on rainin’, the levee’s gonna
break. I am flooded with emails. If we water the seed of that idea, perhaps it
will come to fruition. This text is so dry that it needs a dry sense of humor
to keep readers thirsty for more. We’re all water.
We may
talk, write, sing, and think about water, but how much do we know? Everything
(when we sing, perhaps)…and nothing (much of the rest of the time). As long as
we somehow manage to keep physically hydrated (this can occur through force of
habit and unconscious reflex as easily as it does through considered action),
we can survive bodily even if our intellectual understanding of water is desiccated—even
if our mind is a desert.
Most plants
we grow are a little different. For them, water is not a concept or a metaphor.
If we as gardeners treat water for our plants as simply a concept or a
metaphor, we may soon find that our garden is full of more concepts and
metaphors than plants.
In other
words, water is important.
Water is
essential for plants’ metabolic processes of transpiration, nutrient uptake,
photosynthesis, and growth. It is also essential for the metabolic processes of
the soil microorganisms upon which our plants depend. In a desiccated soil, most
life processes grind to a halt, awaiting the return of moisture. When we search
Mars for signs of life, we look for evidence of water. When we search our
gardens for signs of life, we need to do the same.
During much
of the fall, winter, and spring, plenty of water falls from the sky to keep our
gardens well-watered. We usually do not need to begin regular outside
irrigation until June (or, in a dry year, May). And sometime in September or
October, the need for our own outside irrigation usually stops, as the Great
Irrigator takes over once again.
In
greenhouse beds, we need to water year-round. However, during the short, cool,
moist days of winter, evaporation of moisture from the soil inside the
greenhouse is greatly reduced, and plant metabolism and water loss through
transpiration are slowed as well. Water also seeps in from the soil surrounding
the greenhouse, raising the water table under greenhouse beds. Whereas we may
need to irrigate every five to seven days during the summer, we may go a month
or more without needing to add any water to greenhouse beds during the winter.
The only
significant exceptions to the above occur with seedlings and young plants,
which often need frequent water even when the rest of the garden doesn’t. Seedflats
and seedbeds need fairly constant moisture in order to sprout. Just-sprouted
seedlings can require watering once or even multiple times a day (especially if
in trays), depending on the season and the weather. Starts in seedflats, trays,
cells, and pots often need significantly more frequent watering than those in
garden beds, because the small amounts of soil they are planted in dry out more
rapidly than the larger reservoirs of soil in the garden. In fact, on hot,
sunny days, starts in containers inside and outside the greenhouse may require
watering every hour or two, especially at midday and in early afternoon, to prevent
them from drying out. It’s important to guard against the formation of a baked
crusty layer on top of seedling cells—it may prevent the future penetration of
moisture.
After
transplanting into the garden, plants are watered in immediately and then often given a
follow-up watering within the next few days. As plants grow and establish
deeper roots, watering can become less frequent. After the first week or so, except
in very hot weather, we usually revert to a once-every-five-to-seven days
watering protocol. Tapering off the watering to these less-frequent, deep waterings
encourages roots to penetrate deeper into the soil, which helps the plant take
up more nutrients and also guards it against future drought or physical disruption.
Vegetable
plants, once established, generally need about one inch of water per week
during their growing season. We set out buckets (very much like the one which
stars in the Beetless’ MAXWELL'S PLASTIC BUCKET) or other containers to catch
irrigation water and/or rain, so as to monitor whether plants are receiving
this amount. Some plants, like celery (bred from a wetland plant), are known to
be particularly water-thirsty, so for best results they will receive more than
one inch of water per week. On the other hand, tomato plants produce better
results when we irrigate them as little as possible; they will fruit sooner and
more abundantly, and fruits will have better taste and be less prone to split,
if they receive little or no water except when the plants are obviously under
stress from drought. The best tomatoes in the world are reputed to be
dry-farmed tomatoes from a field in California (which tap into an underground
water table but do not receive any additional irrigation).
Some
plants, like squash, cucumbers, beans, peas, and tomatoes, may be prone to
disease or rot if their leaves (or fruit, if sitting on the soil) stay wet for
extended periods. In these cases, watering overnight or in the morning, so that
leaves have a chance to dry off during the day, is preferable to watering in
the afternoon or evening, which will result in more continuous hours of wetness.
(Drip irrigation is another alternative which helps keep leaves of these plants
dry.) Wet soil surfaces also encourage slugs, so during slug season, it’s best
to time waterings (especially in areas featuring favorite slug foods like young
salad greens and low-lying ripening tomatoes) so that bed surfaces dry out
before nightfall. On the other hand, watering a not-yet-sprouted seedbed so
that it will stay moist overnight usually makes sense.
We have
used several different types of watering implements and systems. Approaches to
watering can be divided into two major categories: overhead and drip. Overhead
irrigation most closely mimics natural rainfall, and has many advantages.
Instead of creating zones of wetness and dryness (as drip irrigation usually
does), overhead irrigation moistens the soil evenly. One of John Jeavons’ most
important pieces of advice, “Don’t grow plants—grow soi,” could be applied
equally well to irrigation: “Don’t water plants—water soil organisms.” In some
cases, watering individual plants may be the best choice—but if water supplies
are adequate, a healthier soil ecosystem and garden ecosystem will result from giving
all of the soil, not just narrow strips of it, access to life-supporting water.
Overhead
irrigation keeps our diverse, multigenerational, nonlinear plantings
(incorporating the volunteers that pop up all over our gardens) thriving. It
allows us to plant in curved, rather than straight beds. It rinses dust off of
leaves. It releases mood-enhancing negative ions into the air, and can cool
gardeners on hot days. It nourishes the soil. It also uses durable irrigation
equipment, including impact sprinklers (celebrated in the Beetless’ RAINBIRD),
oscillating sprinklers, “poke” sprinklers, watering wands, and
lifetime-guaranteed reinforced hoses.
On the
other hand, even when done correctly, overhead irrigation consumes more water
than drip irrigation per given area. Drip irrigation prevents loss of water to
the air, keeps water off leaves (increasing dust buildup, but decreasing the
dangers of disease spread and slug attack), and concentrates water where crops
are planted (thus discouraging the growth of not only volunteers and potential
interplanted crops, but also “weeds”). On a large scale, accompanying less
diverse planting layouts, it can thus lead to greater efficiencies by reducing
not only water use and potential disease and pest problems, but the need to
weed. Drip irrigation also requires less water pressure than overhead
irrigation, so it may be more amenable to lower-tech, pumpless water systems
involving cisterns, tanks, and/or springs. This is especially relevant if (as
at Lost Valley) the landscape does not have
adequate elevation change to create higher pressure without pumping water into
a raised tower.
Among their
technological drawbacks, drip irrigation lines may require more maintenance,
have shorter life-spans, and produce more plastic waste than non-drip systems.
They also require higher initial money investment. We have used drip irrigation
on occasion in the Lost Valley vegetable gardens, but have usually
ended up supplementing it with overhead irrigation anyway. Satisfactory drip
irrigation systems are certainly possible to establish, but for a host of
reasons, many of them enumerated above, we have usually chosen to stay with
overhead irrigation at Lost Valley.
We overhead
irrigate at night whenever possible, to minimize loss of water to the air
through evaporation. Both the sun and the wind, if present, tend to be more
intense during the day; water emitted in nighttime irrigations soaks into the
soil much more thoroughly. Nighttime watering also guards against the danger
that magnified sunlight defracted by water droplets will burn plant leaves.
When set to spray in a wide circle, our impact sprinklers lay down about an
inch of water in 12-14 hours; oscillating sprinklers, covering a smaller area,
can do the same in 3-5 hours; poke sprinklers in less than an hour.
Greenhouse-bed watering with oscillating sprinklers can’t be done overnight
without producing flooding, so we time it when possible for the morning or
evening. Because greenhouse plastic reduces sun intensity and evaporation somewhat,
we occasionally water greenhouses even when the sun is shining into them—sometimes
because of other scheduling considerations, and sometimes simply to cool them
down.
A few words
of caution: On sunny days, water sitting in hoses may become hot. Therefore, before
watering starts at the greenhouse or spot-watering other plants, we always run
water out of the hose until it’s a plant-friendly temperature. In order to
prolong hose life (which is shortened under continuous pressure), we also take
care to turn off water at the tap, and to release pressure from the hose by
leaving the watering implement valve open, at the end of any watering process.
(Even if the tap is closed, a closed end on the hose can cause an increase in
pressure when the water trapped inside warms up in the sun.)
Water
should never be applied to the surface of the soil in such quantities or at
such speeds that it cannot be absorbed. YOU'RE GONNA LOSE THAT SOIL warns of
the dangers of soil erosion when water is not applied gently, while THE LONG ERODED PATH indirectly suggests a possible outcome of such human-created
flooding. The “Beetless Bootleg” APPENDIX lists two additional watering
songs—DON’T LET ME DROWN and WHILE MY DRIP TAPE GENTLY SEEPS—but lyrics,
unfortunately, have been lost.
Fortunately,
no matter what particular methods or equipment a gardener uses, she or he will
inevitably reach the same conclusion with which we began this section:
Water is
important. It gives us the capacity not only for life, but to be grateful for
life…and grateful for irrigation, without which, every summer, most of us vegetable
gardeners in the Pacific Northwest would be up a dry creekbed without a paddle.
(forward to Pt. 9) (back to Gardening Guide index)