In a 1997 essay entitled “The Sinking City” by Joel Simon (Published in a great collection called The Mexico Reader, Joseph and Henderson, editors, Duke University Press), Mr. Simon paints a sobering picture of Mexico City’s water situation. The city sits on a dry lake bed, and the majority of the water used by the rapidly growing city is pumped from the aquifer below the city. This has resulted in the slow but steady sinking of the city as the water is pulled out and the city settles downward. Some areas of the city have fallen 25 feet in the last century.

The sinking of Mexico City has itself become a water problem, According to Simon, the sinking has ruptured so many pipes that 30 percent of Mexico City’s water is lost in the ground. This is no small figure. City water commissioner (at the time)Senor Alfonso Martinez Baca estimated the figure at 36,000 liters (about 9520 gallons) per second! That’s over 411 million gallons a day, lost to broken pipes. In irrigation terms, that’s 1261 acre-feet per day!

Here on the farm, we are keenly sensitive to such numbers. Blanco County and all of Central Texas is still locked in an historic drought, and the Blanco River near our farm has stopped running completely. Everywhere we go, the question we get is “How are those wells holding up?” What we are really being asked is “How much water are we using?”. Water issues have come to the forefront in our county as we face heavy development pressure out of San Antonio. Just a month or so ago, a large development filed for and received a well permit for a huge golf course and subdivision. An angry mob of the citizenry is rattling gates and raising the torches against this development, and any other perceived water use threats. Even though our water use is a fraction of what the golf course will use, we are keeping a low profile these days!

We are quick to point out, however, that all of our irrigation is done with drip irrigation, and that nothing is wasted. People are very open to listening to our explanations, and usually come away with the understanding that we are conscientious water users, and that we make every effort to conserve. We also point out that by farming, we have essentially protected our 130 acres from the type of development they are concerned about.

We have always used drip irrigation. That is a fact of life when farming in Texas. Over the years, we have figured out how to simplify our irrigation systems, and we have learned a lot of shortcuts and cost-saving tips. And since most of our crew is from Mexico, we have also learned how to explain it all in Spanish, and how to watch out for the pitfalls that Mexico City has to deal with! We’ll try to explain our irrigation system to you here.

Drip tape
We use T-tape irrigation in all our beds. T-tape is a brand of bi-wall irrigation tape, and there are many other brands, but the name T-tape has become the generic name for all bi-wall irrigation, just as “Kleenex” has become the word for all facial tissue. So when we use the term T-tape, we mean any bi-wall irrigation tape.

Bi-wall irrigation tape is actually one small tube with drip emitters fused to a larger tube that carries the water. The basic concept is this: if you punched a drip hole every 12 inches in a single wall tube, the holes nearest the source (the header) would drip out the largest amount of water, and as you went farther down the line, less water would be emitted, until at the end, possibly, no water would be coming out. Bi-wall tape equalizes this water distribution by fusing a second, smaller tube on the larger tube. The water from the big tube fills up the smaller tube, which then equalizes the distribution down the entire line for uniform application of water from one end to the other. 200 feet is about the limit of uniform application for most brands of bi-wall. Longer runs start to lose uniformity after that.

T-tape comes in a variety of thicknesses and drip emitter spacing. We use a 12-inch spacing between emitters. You can get them at closer or wider spacing, depending on your needs. Keep in mind that a closer spacing will require more water volume, but perhaps less time running. We generally run our systems for 24 hours, and a block of beds gets irrigated about every 5 days. This is in the heat of the summer.

The thickness of the tape is measured in millimeters. A “6 mil” tape means that the thickness of the plastic is .6 millimeters. Likewise for 8 mil and others. 8 mil seems to be the most commonly used thickness. Drip tape was originally made to be a “disposable” irrigation technique, but most sustainable farmers we know instinctively try to limit their use of plastics, and most of us try to reuse the tape for as many seasons as we can. You might think that using a heavier tape would be better for longevity, but we have actually gone in the opposite direction. We now use a 6 mil tape. We can generally get 2 or more seasons from a line of drip tape, and the main reason we have to replace tape is because animals have chewed through it. A rabbit will chew through 8 mil and 10 mil tape just as easily as our 6 mil, so heavier tape was no advantage. Also, 6 mil tape is less expensive per foot. We get 10,000 feet on a roll of 6 mil, whereas a roll of 8 mil holds 7500 feet. The cost per roll is about the same. The 6 mil holds up just as long for us as the 8 mil.

Filters and pressure regulators
When you are setting up a T-tape system for the first time, you will find that your irrigation supplier has all sorts of bells and whistles to go along with the system. We have learned that a lot of these can be done without. First is a filter. We are lucky enough to live in an area where our well pumps cleanly, without a lot of sediment, so we don’t use a filter. But if your well has any kind of sediment, or if you are using surface water, you will need a filter. Look for one that is “self-cleaning,” meaning that it has a valve on the end so that you can simply open and flush the filter periodically without actually opening the filter itself to clean the screen. For surface water, you’ll be dealing with a lot of algae and organic matter, and you’ll want to look into a sand filter. These things are shaped like a barrel, and hold about 100 pounds of fine sand. The water is forced through the sand, and the sand traps all the particles. They need to be back flushed a lot to clean them out. We found that the most economical place to get a sand filter was at the local swimming pool supply. They’ll have them, and the grade of sand you need.

The next thing you’ll look at is a pressure regulator. Drip tape is made to operate at low pressure, maximum 10 PSI for up to 10-mil tape or 15 PSI for 15-mil tape. We haven’t used one in years. Now, through trial and error(plenty of error!), we have figured out how many systems we need to run, or how much to open the valve, to get the desired pressure.

Most wells operate at a cut-on/cutoff pressure setting of either 30/50 or 40/60 psi. That means that when the operating pressure in your lines falls below 30 psi (or 40), the well pump will cut on. This is way more that drip tape can handle, and it will explode from the pressure. But out in the field, the more systems that are running, the lower the operating pressure at each system. We have our well set on a 40/60 pump switch, and we have found that by running 4 or 5 systems at a time, each with six 200-foot beds per system, we end up with a satisfactory pressure and volume of water in each system. We learned that too many open systems lowered the volume so that not enough water got to the ends of the line, and fewer systems open would be too much pressure. Of course the other way to lower the pressure is to simply close the valve a bit. On systems with fewer beds, we just crack the valve open a bit. You’ll know it is right when the full drip tape is firm to the touch but not hard. There should be some give.

Supply lines
Very little of our supply pipe in the field is buried. Only one main 2-inch line is underground. In our opinion, buried pipe means lots of digging, because the risers are always getting broken off and lines are always getting plowed up. We come up out of the ground from the 2-inch line with several 1-inch lines of black poly tubing. The 1-inch poly line runs along the ends of the beds and there is a ball valve with a garden hose connector about every 75-100 feet. Beds on either side of a driveway share one of these 1-inch poly supply lines. Each valve has a garden hose or 1/2-inch poly line that is moved around and connected to different systems as needed. Each valve serves about 4 or 5 irrigation systems, and we will run 4 or 5 valves at a time per well. The advantage to this system is that when needed, all the irrigation lines can be rolled up out of the way for cultivating or cleaning up. Also, if we accidentally cut a 1 inch supply line with a tiller or other tool, as will happen, there is no digging. A quick splice with a connector and hose clamps takes care of it.

Beds per system
Now lets talk about each individual system. We set up a standard bed system at our farm, with each bed being 200 feet long. We have 6 beds in each irrigation system, and the beds are all 4 feet wide. Our standard planting is 4 rows per 4-foot bed, and we use two lines of drip tape per bed. So usually we have twelve 200-foot long lines of tape per system. Sometimes we plant six lines of plants per bed, and then we use 3 lines of tape per bed. At the head of each system, we have a header line of 1/2- inch black poly tubing. We know this as the “cabecera” in Spanish. 1/2-inch black poly tubing is the most common irrigation tubing size, and you can buy all types of connectors that are called compression connectors. They have no threads or clamps. You simply force the cut end of the 1/2 inch poly into the compression fitting on the connector. Force is the operative word here! You have to work at getting it in, but once the tubing is in, they hold like a finger in a chinese handcuff. It is next to impossible to get the tube back out!

At one end of our header, we use a compression connector with a female garden hose end. Along the header, at each bed, we install 2 or 3 “twist-lock” connectors that connect the drip tape to the poly header. These are known as “chipones” around here. They have a barbed prong that pops into the header.

You will need to buy an inexpensive hole punch for the size of the prong. You make the hole, and then push the connector into the header. Then you slip the tape over the other end, twist the outer ring, and the tape is secure. We always give the tape a firm tug at this point to be sure it won’t come loose during the night. (It will always come loose at night, so that in the morning you have a flooded area that the crew will, inevitably, get the truck stuck in!)

We run the lines of tape off the spool and down the row by sticking a piece of pipe through the spool. You can set two spools on a frame and pull 2 rows at a time, or if you are by yourself, set one spool on a longer pipe and set that inside a wheelbarrow. Point the handles toward the bed and slowly pull out the tape. We tie a knot in the far end of the tape when we reach the end. Irrigation suppliers will sell you expensive little connectors to plug those ends, and we’ve seen other growers make little envelopes with pieces of T-tape into which they fold and insert the end of the line. Good grief! Just tie a knot!

To close the end of the header, we just fold it over. Again, you could buy a fancy little figure-eight doodad that you slip over the end and then fold the pipe and stick it through again, but you’ll just lose these eventually. We just fold it over and tie it with an old piece of T-tape. You’ll have lots of that around!

Repairing the system
Maintenance is more that half of the work with an irrigation system. There is always something cutting or biting into the lines. Frank believes that PVC pipe sticking out of the ground has a magnetic attraction (otherwise unknown to science) to rear bumpers of trucks and tractor equipment. Put up a PVC irrigation riser and someone will back over it–guaranteed! For this reason, all of our risers are connected to the main 2-inch line with threaded connectors at the joint. In theory, the pipe will break off, and you will be able to unscrew the stub and screw in a new connector and pipe. However, the physics of PVC are such that the strongest (and hardest to get to) joints break before the weak pieces of pipe, so you still end up digging the whole thing up.

With our six-bed systems, things are always getting cut or chewed up. When we change out crops in a bed, we usually only change one or two beds at a time, so we pull out the tape, but leave the header in place. Then we till the beds, and of course the tiller catches the headers and chews it up. Luckily you can buy compression connectors that will splice 1/2-inch poly line! We use a lot. Another tip. When you need to close off the chipones (T-tape connectors) on just one or two beds on a system, don’t buy those expensive chipones with a little ball valve in them. Just tie a knot in a 1-foot piece of T-tape and stub out the connector.

Inevitably, someone will cut through the tape when harvesting (especially in statice), and in drought years like we are having, animals will chew through the tape to get water, so we are always repairing the lines of T-tape. This is where we start to feel like Senor Baca in Mexico City. There are a lot of rabbits out there, and boy are they thirsty! To repair a hole in the T-tape, you can buy a fancy repair splice – essentially a chipone with two ends. But we learned a trick from Larry Butler at Boggy Creek Farm in Austin. He showed us that a 3-inch piece of 1/2’-inch CPVC (the hot water kind) fits perfectly inside a piece of T-tape. We call them “tubitos “–little tubes, in English. Slide the tape over the pipe, and then take a short piece of concrete tie-rod wire (You can get a roll at any hardware store) and go around the tubito twice with the wire, and then twist it tight with a pair of pliers. Do the same with the other end, and you have a splice for just a few cents. We pull the tubitos out of the old tape and reuse them. Frank likes to tie a bit of flagging tape at the tubitos so you don’t cut your hand on the wire when you are pulling the tape out.

Without constant maintenance, any irrigation system would soon deteriorate into a leaking mess. In order to prevent a Mexico City-like situation, every truck on our farm carries a repair bucket with all the tools, supplies and connectors that we need. If repairs are done as they are needed, you will avoid a lot of trouble down the line. Frank used to work for a big greenhouse company, and the owner would always say, “Take care of the little things, and the big things take care of themselves”. How true. So our repair buckets all have a supply of tubitos and wire, lots of connectors and chipones, hose washers, small electrical pliers, screwdrivers, and a knife, among various other things. We have everyone fix the systems when they see a problem. We pull out the lines of drip tape sometimes 3 or 4 times a year to prepare beds, and old lines are inspected every time they go back in. We have had to stay up on the crew to insist that they pressurize and repair every installation, even if we won’t be operating it right away. Old T-tape lines get up to two repairs, but after that we pull out the tubitos and put in a new line.

Say it in Spanish
We have our system pretty well worked out now, but sometimes there have been some real cultural challenges trying to implement our irrigation system with our Mexican crew. Turns out the Mexico City analogy was not too far from the mark! One thing that used to drive Frank crazy was that the crew would find a leak, and using a piece of cellophane or clear plastic bag, they would tie a perfect little bandage over the leak. Big holes, little holes, it didn’t matter. Of course, in a pressurized system, all this did was hide the leak–it didn’t staunch the flow. So sooner or later Frank would be driving up the beds on the tractor and suddenly the front tires would sink to the axle where a swamp had been quietly forming. We would correct the guys, but every spring they seemed to go back to the “bread bag” repair system. Cripes. Then one time we were traveling in Mexico’s Copper Canyon, and there, on the 2-inch poly line that led to the town at the bottom of the canyon, were numerous bread bags tied all over the line! Water was spurting out all over. It was a miracle any water made it to the town at all. Frank felt so much better! Apparently, the bread bags were standard operating procedure. We have since seen this in other places, too. We now have an experienced crew, and they all know how to repair the system properly, but anytime a new fellow joins the crew, we know what to look for. Senor Baca in Mexico City has our deepest respect! ï ¹

Frank and Pamela Arnosky are the owners of Texas Specialty Cut Flowers in Blanco, Texas. For more information on their farm, visit www.texascolor.com or email them at arnosky@moment.net. They write about cut flowers regularly in Growing for Market.