Supply

The first step in planning is to determine our water supply. In this case, it is clean municipal water and the rate of flow is a consistent 600 gallons per hour at the source (10 gallons per minute).

Plants

We have 50 plants per row and 32 rows for a total of 1600 plants. Each plant needs one gallon per day for a total of 1600 gallons per day. The number of circuits we can plan is limited by the diameter of the header and branch tubing. In our case, we are using regular 1/2" tubing which has a maximum flow rate of 180 to 200 gallons per hour.

Let's plan on watering one eighth of our plants at a time. We will have eight circuits and each circuit will turn on at a different time of day and will deliver 200 gallons per hour. (See Alternate Header below for an easy way to increase the number of rows serviced by each header)

Since we have 600 gallons per hour from our source, we could easily program two circuits to start and run at the same time without outstripping our source.

Rows

Next we know that we should keep the row lengths as short as practical. The original row length of 200 feet will result in a pressure drop due to friction in the tubing. So let's cut those long rows in half by installing our 1" high-pressure supply tubing across the middle of the field. That way our rows are only 100 feet long.

Supply line

The 1" supply line can be black plastic water tubing or white PVC pipe and will be available at any local plumbing supply along with fittings. The 1" supply tubing will be operating at the same pressure as our municipal supply, which is normally about 50 PSI. The advantage to maintaining high pressure for as long as possible is that we will have less pressure loss in the pipe. In our case, the supply line is short but if it were longer, 1-1/2" tubing may be better and will keep the loss of pressure to a minimum. You may want to add a gate valve at each timer to be able to close and isolate each circuit for easy maintenance. Gate valves are available at any local plumbing shop.

Filter

We will add an anti-syphon valve and a disc filter at the start of the 1" supply line. The anti-syphon valve in this case will be a heavy duty brass unit from a local plumbing supplier and the disc filter is available at our online store (FLR5)

Standpipe

At the start of each circuit, we will build a standpipe and attach a battery-operated timer (TM6), a 22 PSI professional pressure regulator (PR5), a pipe thread to hose thread adaptor (FA18), and an compression adaptor (FC16) to attach to the 1/2" tubing that supplies water to a header and to each row. (See How-To for a standpipe construction article) These four parts make up our faucet assembly.

Detail of faucet assemblies at each of four circuits

Header

Now we will add a header for each circuit. That will be a length of 1/2" tubing that starts at the faucet assembly of each circuit and runs parallel to the 1" supply tubing for about 36 feet. All the 1/2" tubing for the rows tees off the header. There will be 8 rows 100 feet long per circuit.

Alternate Header - a neat trick

If we use an FC18 adaptor in place of the FC16 mentioned above, it splits the output from the regulator and we can double the output to our headers. That way we can increase the number of rows in each circuit and the total flow in the circuit increases from 180 gph to 360 gph.

Rows

Last, we install tees and the 1/2" tubing for each row. Since the plants are spaced far apart, we will install a dripper at each plant. That way we can be sure to get the spacing exact with a dripper at the base of each plant. If the crop was close-spaced in the row, we may have chosen dripline which has drippers installed at the factory and saves us the time installing drippers.

Setup

Once the system is complete, flushed and tested, we will program the timers to come on at various hours of the day, usually before noon so that each plant has water available at the roots in the middle of the day when transpiration is at its highest. Timers permit multiple start times each day if required. The 1" supply tubing can be left on and pressurized all day and the timers at each circuit control the flow of water to the rows.

Summary of Planning Principles