In-line Growth

The photo on the left shows in-line drip irrigation tubing placed over the landscape as recommend in my book Drip Irrigation, for Every Landscape & All Climates. The right photo is a bit over one month of growth. Good growth. less water.

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My Garden

A view of my little garden. I let the foxglove "walk around". A different pleasure each year. This section was drip irrigated for three years, then 20 years without irrigation. Not a benefit to a publisher of my book Drip Irrigation for Every Landscape All Climates.

Get Your Wet Spots Figured Out

The drawing in the middle is from my book Drip Irrigation – For Every Landscapes & All Climates, it shows an ideal view of how the wet spots on the surface merge together 2-6 inches below the soil’s surface. The photo on the left shows the spots of irrigation on the surface of potting soil filling a horse trough. Notice how much of the soil appears to be dry. The other photograph shows the soil after I created a hole 4 inches deep – moisture is in the entire block of soil. These emitters are the 1/4-inch inline tubing with emitters every 12 inches. I’ll show, in later blogs, the resulting growth.


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Drip Increases Yields, much of the time

Numero uno is one of the often poorly-understood concepts about drip irrigation.

There are many scientific studies which indicate that drip irrigation can improve growth and yields. For example, in 1981 T. A. Howell et al surveyed 50 research reports on crops grown with drip irrigation, and concluded: “Where trickle [drip] irrigation was compared with either no irrigation or other water-application methods, yields were equal or better in all cases; and the amounts of water applied were equal or less with only two exceptions.” (As summarized by D. A. Bucks and F. S. Nakayama and A. W. Warrick in “Principles, Practices, and Potentialities of Trickle (Drip) Irrigation,” Advances in Irrigation, Vol. 1).

Research in many different climates and states invariably supports the benefits and cost-effectiveness of drip irrigation. Art Gaus, an extension horticulture specialist with the University of Missouri at Columbia, MO, has had a drip system in his personal garden for nine years. One summer, his bush watermelons with plastic mulch and a drip system produced 32 pounds in a four-by-four-foot area, compared with 9–16 pounds in the same area with conventional irrigation. He reckoned a well-timed drip system “could mean a 100% increase in yields; during the droughts of 1980, ’83, and ’84, it meant the difference between having a crop or no crop at all.”

In a study of established pecan trees in Georgia, trees with drip irrigation added had a 51% increase in yields.

Michigan State University has documented a 30% yield increase in vegetable crops with drip irrigation, even in its humid, summer-rain climate.

A study in India in 2002, found that with chilies, water use was down 34–50%, while production was up 33–48%. The researchers attributed this to irrigation that kept the soil moist, not too dry.

A study in New Mexico found amazing differences in yields compared to [respectively] furrow and drip irrigation: 18 pounds versus 30 pounds with cucumbers, 69 to 156 pounds growing Swiss chard, and 64 versus 166 pounds with green beans—to quote a bit of the study. [It is interesting to note that broccoli, Brussels sprouts, and carrots didn’t have any greater yields in the drip irrigation plots. Yet, a study at Oregon State University found a 20% increase in carrots compared to plots with sprinklers.]

To be fair, the benefits of drip irrigation are not confirmed across the board in agricultural studies. There are a number of studies which show it to be less beneficial than sprinklers, especially with perennial and tree crops. One such example is found in a paper entitled “Growth and Yield of Rabbiteye Blueberry as Affected by Orchard Floor Management Practices and Irrigation Geometry,” by K. D. Patten et al. in The Society, September 1989, Journal of the American Society for Horticultural Science, Vol. 114 (5) pg. 724-728. This study found that 360-degree sprinklers created better plant establishment and growth than either one emitter or two emitters per shrub. This is one of many cases where agricultural limitations (such as having to keep the area between tree rows free of tubing and emitters so tractors can mow or disc) greatly restrict both the number of emitters which can be used and their placement. In my drip-irrigation book (Drip Irrigation for Every Landscape and All Climates, 2nd Edition, Metamorphic Press, 2009), I very specifically recommend that emitters be placed equidistant throughout the entire root zone—which would include the area equivalent to that between the rows. The results in the abovementioned study are only to be expected when a dramatically reduced proportion of the root zone is watered by a mere emitter or two.

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Lawn Irrigation That's Really "Out of Sight"

Lawns, yawns. They aren’t needed as much as they are found. However, there's no better place to have young kids run around and, play badminton or croquet, or necking while watching the stars. (This subsurface approach to irrigation means you can neck at the same time the lawn is being irrigated!)

The latest revolution in irrigation is happening quietly underground, four to eight inches beneath lush, but water-conserving lawns. Although landscape professionals have long utilized the water-conserving efficiency of drip irrigation for most other types of plantings; combining it with lawns has, until recently, been an unsolvable problem.

Now, however, it's possible to irrigate lawns with emitters buried safely beneath the soil's surface that save even more than the 20-50% watering efficiency of surface emitters.

The idea of subsurface lawn irrigation often raises many concerns. What, for instance, keeps the entombed emitter from becoming plugged by soil? The answer is in-line emitter tubing. The emitters, which are located inside this tubing, contain a lengthy internal pathway which is known as a complex, turbulent or tortuous path. (See the illustration here from Drip Irrigation for Every Landscape & All Climates.) When the system comes on, water pressure purges any soil that may have entered the emitter's orifice. The turbulent pathway is also very self-cleaning when sediment is suspended in the water.

Another common concern is the possibility of the emitters becoming clogged with grass roots. This can be prevented by timed irrigations, which should be both frequent (daily or even hourly) and very brief. Depending upon the soil and climate, for only a matter of minutes, or less—depending on the number of start times. Some brands of in-line tubing also come impregnated with a pre-emergent herbicide which kills root growth at emitter openings. (The roll photographed here has the noticeable greenish tube emitters.) While no organic gardener would use the Treflan™ found in the impregnated emitter, it’s toxicity is very low and the chemical does not migrate far from the emitter.

Designers and clients also may worry about unevenly-watered lawns with telltale green-brown-green striping. Mark Dargay, of EH Griffith Inc., (a distributor of TechLine™ in-line tubing) designed the subsurface irrigation for the Market Square project, 12,000 square feet of turf and trees in downtown Pittsburgh, PA. "I was very leery," Dargay remembers, "I envisioned striping of the lawns." After two summers of healthy non-striped growth, he’s "very pleased."

A word of caution: neophytes in drip irrigation should make their first mistakes above ground with visible or mulched in-line tubing before attempting a subterranean "deployment."

Dennis Hansen, a L.A. and Certified Irrigation Designer in Fairfield, CA, advises designers new to subsurface irrigation to "start with no more than 1000 square feet. Or, hire an irrigation designer with enough experience to have a defensible and insurable status."

The details of how to design an efficient system can be found in my book— Drip Irrigation for Every Landscape & All Climates.

P.S. DON’T attempt if you have gophers. Best in urban areas.


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Drip Paraphernalia

It' time for tuning up & testing drip systems. If, gawd forbid, you have a a system with lots of punched-in emitters you'll need to carry around spare emitters, a punch, goof plugs & more. Use a box with lots of chambers like the sewing paraphernalia shown on the left. Or, boxes used for fishing hooks & gear or small tool boxes with transparent plastic covers. Although the sewing box is illustrated in my book, Drip Irrigation for Every Landscape & All Climates, you can skip most of these tiny, tedious parts by using in-line tubing where there are no emitters to break off, adjust, or repair. The in-line tubing in this patch of beans (on the right) is streamlined, easy to roll out, and you can never damage the internal emitter. With a two- to four-inch mulch layer over the tubing, you can walk or use a wheelbarrow on top of the tubing with no damage. Light folks can even step on the tubing without damage. Be sure to flush all lines before starting to use the system.

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Drip Tubing for Trees

Tree roots grow one and one-half to two and even three times the width of the foliage above. More amazingly, this ratio is maintained throughout the life of the tree, regardless of the rootstock, species and soil.

These two trees don't understand this basic rule of thumb. The one with two circles has the right idea that trees should be watered in circles. But at least the inner circle with the beige/brown tubing is too close to the trunk. This is at least a waste of tubing. With drought tolerant trees and many other water sensitive roots can receive enough water to cause root rot. Put the emitters further out, near the dripline of the canopy. (Based on the book Drip Irrigation- For Every Landscape and All Climates.)


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Get to Know Your Wet Spots

To test your soil and to understand how emitters work, buy a single emitter, use an emitter punch (which cuts a tiny circular hole) to pierce a hole near the bottom of an empty plastic one-gallon milk jug, and insert the emitter's barb. Fill the jug with water and place it on a dry spot in the garden. After the milk jug is empty (which may take 24 hours or more because it's not under pressure), dig a small trench next to the emitter to see the shape of the wet spot in your soil. This is the most graphic way to understand how the water from each emitter you install will move in your soil. (The shape of the wet spot will change, usually both wider and deeper, when the emitter is used under pressure.) The shape of the moist area is affected differently by each type of garden soil and ranges from long and carrot-like to squat and beet-shaped. Emitters with a higher rating, such as 2 or 4 gph, will cause the wet spot to be wider than 1/2 or 1 gph emitters.

A moist-but-not-too-wet spot that is the key to drip irrigation's superiority over all other forms of irrigation. With proper timing, a drip irrigation system provides moisture to the soil without overly saturating the pore spaces in the soil. The labyrinth of minute pore spaces helps the soil breathe. When a more aerobic condition in the soil is maintained by drip irrigation, the roots don't drown, the soil's beneficial bacteria can continue to release valuable nutrients, and harmful anaerobic fungi don't easily proliferate—thus, better growth and greater yields

The lower chart (From Drip Irrigation for Every Landscape and All Climates) and shows how the water can move in a theoretical soil. The darker the wet spot, the more it is anaerobic.


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Yikes, Don't do this at home!

There's a reason it's called "spaghetti" tubing. Here we see some breeding to make more of a mess in the garden. Avoid the mess with in-line emitter tubing. I favor it over all "spaghetti" for most landscape uses in my book Drip Irrigation, For Every Landscape & All Climates.

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Let me know what you think.Visit my web site to learn about my new book on drip irrigation and other gardening books. Thanks, Robert

Calculating your daily water needs

For referral to the previous post, here's a repeat of an earlier blog. Pick an ET rate (as given from your local Coop. Extension), follow the column down to the square footage of your planting area, and you'll be given the amount of water for each day. Click on the image and load into a page where you can enlarge the image. If this is too complicated, just buy my Drip Irrigation book from my website, www.robertkourik.com :)

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Wet Spots in Your Garden

The wet spot on the surface of the soil is misleading. The wet spots are at certain intervals, but don't represent what is going on. The photo on the left shows the misleading wet spots. The drawing on the right (from my book Drip Irrigation of Every Landscape and All Climates) shows that the wet spots beneath each emitter merge to form one continous zone of moisture. The soil for the entire length of the in-line tubing is moist some four to six inches beneath the surface, depending on the soil type. Sandier soils require tubing with the emitters pre-installed 12 inches apart. While heavier, clayey soils only need emitters every 24 inches.

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Proper Drip Irrigation Layout

In Drip Irrigation, For Every Landscape and All Climates, I recommend laying out parallel lines, or “laterals,” of tubing throughout the entire bed. I always stock the 1/2-gph, 12-inch-interval version because I install drip systems for different clients with different types of soil. The 1/2-gph tubing with the 12-inch spacing along the hose’s length is the only one that will water sandy soil. You can have your local irrigation supplier order tubing with 6-inch spacing in the drip hose. Yet, clay-loam soils can also be irrigated by turning on the system for a shorter period of time because the water easily spreads laterally. The parallel lines of tubing might be as close together as 6 or 12 inches in sandy soils and as far apart as 24 inches in heavy clay-loams. If you have a fairly heavy soil and want to save money, buy the tubing with 18-inch or 24-inch intervals between emitters, and you’ll save 25% or 40% respectively. Also, a higher flow rate, such as 1 gph, will help the water to spread wider than with the slower 1/2-gph emitter tubing. At worst, you’ll just have to run the system a little longer to get the wet spots to meet underground along the length of the tubing.

The photo on the left was taken at a winery here in Sonoma County. The one on the right I found at a museum in Paris, France. It's really catching on even though there is no French version of my book, as far as I know!

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Special Drip Irrigation Book Sale - the 2nd Edition

This Holiday Season, Give the Gift that Keeps On Giving

...one drop at a time.

Drip Irrigation for Every Landscape and All Climates

“Fun book, great info. Buy it and save the world’s water supply.”

— Jim McCausland, at Sunset Magazine’s blogsite “Dirt”

Special offer: Only $20 [lists for $24.95] No tax. Autograph included.

Includes Free Priority Mail!

Buy From the Source So Writers Can Keep on Writing®

Go to www.robertkourik.com to order via PayPal.

Or, send a check made out to Metamorphic Press to: Metamorphic Press, PO Box 412, Occidental, CA 95465

Information about the book:

As a celebration of its 25th anniversary, the highly respected newsletter Avant

Gardener published a list headed “The 25 Best Gardening Books of the Past

25 Years.” Up there on that list, at number seven, was the first edition of Drip

Irrigation for Every Landscape and All Climates. Great then, even better now.

Yes, Drip Irrigation for Every Landscape and All Climates, by Robert Kourik,

is now available in an updated second edition. It will give you the knowhow

to optimize your water use, survive a protracted drought, or work with the

unpredictable intermittent rains of certain climates. Its light-hearted approach,

step-by-step instructions and clearly drawn diagrams will allow you to construct

and streamline your own drip-irrigation system without the clutter of superfluous

widgets and gizmos.

Drip Irrigation for Every Landscape and All Climates also describes, in clear

and scientific terms, how drip-irrigation systems can be designed or reconfigured

to use less water while increasing yields of fruits and vegetables and improving

the growth of all plants. New in this edition are descriptions of how to use two

very important water sources—grey water and cisterns—as well as how to utilize

satellite control or a home-based weather station to irrigate your garden with

precision.

In short, this fully revised edition of the original ground-breaking book is designed to 1) help gardeners manage

precious water supplies with ease and efficiency, and 2) create sustainable water-efficient gardens and landscapes with the latest technologies of drip irrigation.

Page Count —192 (74 more pages than the 1993 edition)

Number of illustrations—89 B&W (21 new B&W illustrations)

Includes: A Bibliography, Glossary, Web sites to explore (new to this addition), and an expanded and detailed Index.

My Virgin Kiwi Fruits

I usually cut my kiwi vines back very hard to allow for their cascade of foliage to keep my house cooler during the summer and the Indian summers. This year I was rushing to finish the revised edition of Drip Irrigation, for Every Landscape & All Climates, so the vines didn't get pruned. I've had flowers before, but this year one of the two vines brought forth dozens of flowers. Now I have dozens of fruit even though the male vine did not bloom. This is called "parthenogenesis". Fruit produced without any male fertilization. Explain that to me! Will wonders never cease. If it's like the last time this happened ten years ago, the fruits won't ripen until March! (Here the vines are cascading down two stories and out 15 feet.)

Let me know what you think.

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Lessons From "Our" Droughts

As winter approaches, gardeners in the west now have three things on their minds—water, water, and water. Or, rather, the lack of it. The pale, arid shadow of a dusty drought now extends over much of the American west and southwest.

The drought, which has settled into much of the west over the past three years, doesn't make much noise. You can't hear the sound of the mud drying in the bottoms of empty reservoirs. You don't hear any noise from the leaves as they turn brown and fall off the trees in mid-summer. And you can't hear anything coming from the countless wells which have run dry.

The first drought for me, after moving to California, was the so-called Big Drought of 1975-1977. Our current drought, which has lingered for three long, parched years, has had its impact on wild lands, suburbs, and cities. Now, I get to improve my skills with gray water systems, drip irrigation, and xeriscape (drought resistant) planting techniques.

My first experiments with gray water systems—collecting water from sinks, showers, and laundries to irrigate fruit trees and ornamental landscaping—were during the 1970's drought. The systems I installed in the basements and crawl-spaces of clients throughout Marin county in those days were, in retrospect, a rag-tag, baling-wire collection of bizarre-looking gizmos. Now I’ve learned a lot more. See the photo on the left of a system designed with current “technology”.

In my experience, gray water is not a crisis-intervention scheme, but one of the many "tools" which allows my garden to flourish. The overwhelming feedback, and my personal experience, has been: "My plants are growing better with gray water than with any other water source."

I knew nothing about drip irrigation until the drought of the 70's. Again, the "Big" drought introduced me to a new gardening tool which has become commonplace in the 1990's. The technological advances in drip irrigation since I first started messin' with drip irrigation in 1975 have practically exceeded that of the revolution in the computer industry.

After experimenting with countless drip irrigation widgets and gadgets I've settled on my favorite emitter technology—in-line emitters. (As described in my updated edition of Drip Irrigation, For Every Landscape and All Climates. 2009) Unlike the more common punched-in emitter, which you buy separately and insert into a hole you've punched into solid drip irrigation tubing, in-line emitters come pre-fabricated inside the one-half inch drip irrigation hosing. On the right, see the interior of several emitters that become encased in ½-inch tubing. There is also a clear piece of tubing to reveal the emitter. All the real tubing is black or brown. Old-fashioned, punched-in emitters get brittle in the heat and sunlight and easily snap off during routine garden maintenance—which leads to tedious hours of repair. In-line emitters have nothing exposed to break off, are securely housed inside a sturdy one-half inch plastic tubing that'll take to abuse of weeding, gardening, and mulching, and are far less time-consuming since the emitters are preinstalled. With in-line emitters, I avoid the so-called "spaghetti" tubing which seems to somehow mysteriously move and knot itself and ends up resembling its namesake, a heap of tangled noodles.

The drought of the 1990's taught me how to plant so as to practically eliminate the need for drip irrigation. I've come to discover many ornamental Mediterranean plants are actually more drought-resistant than a lot of California native plants. There are small 18-year-old test plantings around my house which were planted at the beginning of our fall rainy season, and never irrigated again.

The first drought for me was the so-called Big Drought of 1975-1977. (By the way, how can a reduced amount of rain, be "bigger"? How can you have more of less?) Anyway, there have been plenty of "bigger" and longer droughts over the past 400 years. Tree ring analysis in the central portion of Santa Barbara county, the Santa Ynez Valley, indicates two periods of 60 years of drought (below "average" rainfall) since the 1500s

So, watch out, don’t count on a break in the drought.

Let me know what you think.

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Winterize Your Drip

It got down to 36F here last night. So, it's almost that time of the year when light frosts begin to glaze the flowers. Soon many parts the country will be having hard freezes.

I've outlined how to get your drip system as described my book Drip Irrigation for Every Landscape & All Climates. Here's an excerpt.

A proper drip irrigation system is too valuable to leave neglected like an abandoned garden hose at each winter’s nippy return. Shut off your system’s water supply at a point inside the house where the water supply is protected from freezing. Loosen all unions at each main assembly to drain all water out of the pipes, filters, pressure regulators, and check valves. Make sure you don’t loose the O-ring which seals each union. Be sure to open the flush ball valve on the Y-filter so the filter chamber doesn’t crack. Better yet, bring the filter or the entire main assembly indoors. Also bring inside any battery-powered controllers which you have attached to faucets.

The drip irrigation hose can stay in place in the landscape, but as much water as possible should be drained out. The photo on the left shows draining a system with a figure eight closer device. Open the end-closures on all lines, let all water drain out, and close. Start at the highest elevation and work downhill. I prefer to use threaded end caps because the Figure-8 end closures (The photo on the left. Not my finger nails.) will quickly wear out the kinked end of the hose. I prefer the threaded end cap for its strength. (The photo on the right.) It’s essential that the water is drained from every low point of the system.

A deep mulch will help protect in cold winter climates. You don’t want anyone stepping on cold plastic tubing, but since many drip systems are primarily located in perennial plantings, the risk of trampling the tubing is low. Some compulsive people do lift out the entire assembly of header and lateral lines, roll up the tubing and store it in the garage for the winter. Porous pipe and in-line emitter tubing make this a lot easier than hose with emitters punched in or hose with, God forbid, spaghetti tubing with emitters.

If possible, lay out your drip irrigation lines so they can all be drained from the low ends. Otherwise, install your drip lines so they naturally drain to various low spots, install an access box at the lowest spot in each line of the system for the winter. Install a manual drain-down valve a simple ball valve. Each fall, the metal drip irrigation ball valve should be opened to fully drain the line.

Lonnie Zamora, a former rooftop-gardener and irrigation designer in New York City, used drip irrigation for over four years on most of his jobs, even in the flower boxes for a penthouse on the 27th floor of a Manhattan apartment building. To winterize his client’s drip irrigation systems each fall, he would:

l Drain the pressure regulator.

l Close the faucet at the home’s wall.

l Attach a 110VAC air compressor with the necessary fittings to the female hose thread at the beginning of the drip system.

l Set the timer to run each line or zone for five to seven minutes.

l Run the air compressor pumps at 25 psi or less to blow out all the lines.

l Manually drain all lines on multilevel, terraced gardens.

l Open the Y-filter’s ball valve to drain the filter cartridge chamber.

Finito!

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Wet Spots & Flavor

It's summer time and the time for a refresher. (From my book Drip Irrigation for Every Landscape and All Climates)

In this illustration, in-line emitter tubing moistens the soil the entire length of the line but slightly below the surface, where the bulbous-shaped wet spots come together to form one nearly continuous moist zone. The emitters come pre-installed in tubing with 12-, 18-, 24-, 36-, and 48-inch spacings [they can be custom ordered at just about any interval—for an extra fee], but the type most commonly sold to gardeners is the 12-inch interval. The emitters inside the hose are rated to dispense either one-half- or one-gph [actually 0.6 and 0.92 gph]. The cost ranges from$22 to $30 for a 100-foot roll depending on the emitter [its emitters flow rate and whether or not it’s pressure compensating.]

If you've grouped your veggies by similar water zones it's time to think about reducing the amount of water a bit to enrich the flavor. Tomatoes are a great example. Over watered 'maters have nothing over store bought. But if tapered off of water once fruiting, the reduced water in the flesh concentrates the flavor. In some climates, you can gradually reduce the water all together by August for the best flavor as the roots are well established after growing throughout the continuous zone of moisture at the beginning of the season. Experiment!


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Frequent Irrigation Can Use Less Water

Most drip systems are up and running by now. Yet, do you know where to start to get the proper amount of water on your flowers and/or vegetables? I'm working on a revised edition of my 1995 classic (so I'm told) Drip Irrigation, For Every Landscape and All climates. Here's an excerpt:

Daily irrigation doesn’t mean using countless gallons of extra water. In fact, with infrequent irrigation, it takes a certain amount of water just to rehydrate the soil before the plant can even make use of the moisture. Oddly enough, infrequent waterings can use more water than the same planting would receive with frequent, even daily, irrigation.

Years ago, for example, I planted a drought-resistant landscape, with plants such as lavender, santolina, rockroses, and rosemary, for a neighbor. The day after planting, the timer was set to irrigate each zone for 15 minutes. After the risk of transplant shock was over, the irrigation lines were turned on each day for only eight minutes. The plants flourished, even though each one-half-gph emitter was distributing the paltry amount of seven tablespoons of water-per-emitter each day. Contrast this with a nearby garden with a similar soil and lavender plants arbitrarily watered only twice a month for four hours. This amounts to two gallons per emitter for the two-week period, or just more than 18 tablespoons of water per day—more than twice the water used in the flourishing landscape.

No matter how you use drip irrigation, frequently or every once in a while, it will always be more efficient than any sprinkler you’re currently using. All sprinklers, except the most modern of micro- or mini-sprinklers, apply water faster than many silty and clayey soils can absorb it. This leads to anaerobic puddling and runoff, especially on steep slopes. Every sprinkler is vulnerable to wind- and sun-induced losses, with as much as 25% of the water wasted. In general, sprinklers are rated at an overall efficiency of 75% to 80%, compared with drip irrigation’s 90%. [Furrow irrigation can have an efficiency rating as low as 50%.]

How Long to Water

There are two general approaches to watering, the empirical and the more analytical, which uses the evapotranspiration rate as a guideline. Each works, but the ET-rate-based approach can be far more accurate and water conserving.

The most immediate, or empirical, way to understand your soil’s response to drip irrigation, and to determine how long to leave the system on, involves digging. Even after doing your experiment with the milk jug, you should test for the drip system’s underground pattern of moisture. Turn on the drip system for an hour, then turn off the hose and dig a number of small holes in the flower bed to see how deep and to what width the water has soaked in. Then turn the system on for another hour, to equal a test total of two hours, and check to see how much farther the water moves. Do this for several more intervals of time and observe vague changes in the wet spot. This test will reveal the shortest length of irrigation time to produce the widest wet spot, based on which test hole revealed the widest spread of the wet spot during the elapsed time. Without doing this test, you’ll just be guessing in the dark.


ET-Based Irrigation

Another approach involves using the ET figures for your local climate. Your local Cooperative Extension office should be able to tell you either the current week’s ET rate or the month’s average rate; both are expressed in inches per day or month. If they don’t know, fire them. (Click on the chart to get a bigger version.)

WARNING: Math Ahead.

The chart above shows the daily water use for ten different ET rates. Remember, the amount of water needed to replace the ET losses depends upon the amount of soil covered [like a shadow] by the planting’s foliage. If the plants are young, the ET rate is less, corresponding to the smaller area of coverage. With a mature flower border, the coverage is complete and all you need to determine is the total square footage of the border. For example, a five- by 20-foot border [100 square feet] uses 18.7 gallons of water per day during a hot day when the ET rate is equivalent to nine inches of water per month. If you still prefer to water once a week, multiply the daily ET rate by seven to determine the total amount for the weekly watering.

To determine the length of each day’s watering, take the total amount of water the flower border requires and divide by the total flow of the drip irrigation system. Consider a theoratical five- by 20-foot border with a daily ET rate of 18.7 gallons. Since the total length of in-line emitter tubing in the bed is 84 feet [this figure is reached by adding together one header four feet long and four 20-foot laterals], the sum flow of the system is 52 gph [84 one-half-gph emitters times their actual flow of 0.62 gph]. Thus, dividing the daily water need of 18.7 gallons by 52 gph yields 0.36 hour, or 22 minutes per day 0.36 of an hour times 60 minutes. If you want to water once per week, then multiply 22 minutes per day times seven days to get a weekly watering time of 154 minutes, or nearly three hours.

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