No matter where you live, whatever your climate, you and your garden can benefit from drip irrigation. Long considered a virtual necessity in the arid climate of California and the southwest, gardeners in regions that receive summer rain know that rain does not fall at regular intervals throughout the growing season. Droughts can occur anywhere, and with the cost of municipal water going ever upward, water conservation is a must. Drip irrigation is the most reliable, efficient, environmentally sound method of watering available to today’s gardeners and growers.
Setting up a drip irrigation system is not that much different than assembling tinker toys: you connect water lines in geometric patterns using connectors in the shape of L’s and T’s. The most basic garden plan, a row or series of rows, is ideal for drip irrigation. There are two basic schemes for drip irrigation with row crops: single rows or double rows. While single row systems are easier to assemble, double row plans make more efficient use of space because they reduce the amount of space devoted to pathways but still allow easy access to your plantings from either side. You can also use a combination of the two, as we do, depending on the crops you grow.
Image to the right: a single line setup.
We use a single row system for tomatoes because we have found that growing them in a single line with open space between them improves air circulation and light penetration. With 3’ between plants the possibility of disease is reduced and weeding and harvesting is easier.
We use a double row system for lettuce, beans, peas, and many other smaller vegetables. A double row system allows you plant on either side of each drip line, creating a bed with four rows of vegetables, each row 12 inches wide for a total of 48 inches. When we set up double rows the standard distance between our drip lines is 24 inches. Our paths are 2 feet wide; each section of our garden is 6 feet wide total.
Image to the right: a double row system. The space between the lines is 24 inches. The large line at the bottom of the image is 3/4-inch PVC.
We use drip tubing with in-line emitters. In-line emitters are pre-installed inside the tubing at set intervals (we use 12” spacing between emitters). The tubing is ready to go when it comes out of the box. All you do is cut to the lengths you need, connect, and turn on the water. You pay for this convenience, but in our experience you get good value because the tubing is highly reliable, nearly maintenance free, and holds up for many years. In the long run in-line emitter tubing takes less time to install and care for and lasts longer than many less expensive products.
The inline emitters are highly engineered components that have several beneficial features. First, they are pressure compensated, which means an equal amount of water comes out of each emitter, even on a slope. Second, the emitters have an internal passageway called a “tortuous path” which creates a vortex. The vortex traps particles and sediment in your
water and carries them out of the emitters. This brilliant design almost completely eliminates plugging. Last, each emitter has an internal check valve which means they all come on simultaneously and shutdown simultaneously. The water dispensed from each emitter is absolutely precise.
You’ll need a second type of tubing, tubing that doesn’t drip, to carry water from your faucet to your drip lines. We call this supply line or solid feeder line. Depending on the size of the area you want to irrigate, you have two main choices for your supply line: blank tubing, which is identical to inline emitter tubing but has no emitters; or PVC pipe. Each has certain characteristics that may make you chose one over the other.
Blank tubing is lightweight, comes in a coil, and is easy to roll out and connect because it is the same diameter as emitter tubing. Connections are made using barbed connectors which are inserted into the tubing. Once inside the tubing they do not come out. No clamps or glueare necessary. The limiting factor of blank tubing is that it is only about ½” in diameter, which means it allows a maximum flow rate of 235 gallons per hour (GPH). This is ample for many gardens, even large gardens, but it may not be enough if you are doing small scale farming. Blank tubing can be cut easily with heavy duty shears, such as Fixars.
Another consideration is that blank tubing is sufficiently elastic and flexible to allow you to leave it outside in the winter. If ice forms inside, the tubing it will not crack. This is useful if you have a permanent garden plan and you don’t want to set up and take down your drip irrigation at the beginning and end of each season. PVC, on the other hand, comes in larger diameters, ¾” and 1”. These carry a maximum of 480 GPH and 780 GPH respectively so you can service a substantially larger area than is possible using blank tubing. PVC is also easy to handle, although you will need a PVC cutter or a saw to cut it and PVC glue to assemble it.
If you use emitter tubing with the emitters every 12 inches, it’s easy to come up with planting schemes that make efficient use of water and garden space. The tubing itself can act as your measuring stick using the set distance between the emitters.
When we plant lettuce we put one plant on each side of the emitter, 6 inches from the tubing,for a total of 12 inches between plants sharing an emitter. Do this down the line and you will have a neat row of lettuce heads, all 12” apart from the nearest heads.
It’s also possible to plant seeds beside drip irrigation lines. This is how we plant peas and beans with the seeds approximately 2 inches apart in the row. However, because the lateral movement of water through the soil, especially at the surface level, is limited, you will need to germinate the seeds by hand watering. After the seeds have germinated and the plants begin to develop their root system, you can withdraw the overhead water and let them continue their growth, relying solely on drip irrigation.
In general, you run a drip irrigation system less in the beginning of the season when the days are cool and your plants are small and longer in the middle and end of the season as the days grow longer and hotter and your plants grow larger. We believe strongly in daily watering to replenish any water lost during the preceding day. This approach maintains even soil moisture and eliminates stress on your plants, protecting them from the extremes of soil that is too dry or too wet.
Late in the season, when our plants are fruiting and require the most water, we run our system twice a day, generally 30 minutes in the morning and 15 - 20 minutes in the late afternoon to replenish the water that evaporates from the soil and transpires through the leaves. This keeps the plants well hydrated and productive. Better yet, we have our system on an automatic timer. While the garden is being watered we are completely free to do something else.
We’ve got an experiment running to see which region of the country has the best conditions for growing tomatoes based on who has the first ripe Oxheart tomato. To see our entry, planted on May 9th, take a look at the TomatoCam.
In my next blog we’ll take a look at drip irrigation for raised bed gardens. See you then!
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