| | Figure 1. Continuous drip line in vegetable garden. |
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| | Figure 2. Close-up of water dripping from hose emitter. |
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Of the many ways to irrigate your garden, a drip system is probably the easiest and is certainly the most effective and efficient.
What Do You Need
Obviously you will need drip tape (Figure 1). Typical drip tape has emitters at 6-, 12- or 18-inch spacings (Figure 2). A 12-inch spacing is most common and probably optimum for general garden use. The conventional method is to run a drip tape line down each row.
An alternative approach that uses half as much tape is to plant your crops in twin drills 6 to 10 inches apart with a wide "middle" between the pairs of rows and then run one drip line between the twin drills. You will also need a header line across the end to feed the drip lines. Drip tape is designed to run at only 8 to 12 psi, so you will need a pressure reducer or regulator. Since the little emitter holes plug easily, you will need some type of filter. You will also need control valves and a way to connect the system to a garden hose or other water source.
Drip and Plastic Mulch
Drip irrigation and plastic mulch go together like milk and cookies. Plastic mulch will reduce evaporation and thus the need for water. It will also help hold the tape in place and will help control weeds.
In a home garden, it is easy to install a drip system, but difficult to install plastic mulch, so most gardeners don’t use plastic mulch. Drip will work fine without mulch; it just works even better with mulch. Organic mulches such as compost are an excellent alternative.
Frequency and Amount
With sprinklers, you generally water the garden, let it dry, water it again, etc. This method won’t work with drip irrigation. With many soils, if you let the soil dry out between irrigations, it will get hard and not absorb water when you next irrigate. Plants don’t grow as well with a wet/dry cycle either; they like consistent moisture. It is much better to drip irrigate lightly but often and thus keep the soil near the correct moisture at all times.
Your drip system should be run daily unless it rains. The length of time you run the irrigation will vary, depending on soil type, drying conditions, crop stage, etc. You want to keep the soil moist, but not wet. Don’t water long enough to get runoff or puddling. In most cases, 30 to 60 minutes a day will be about right, but with large plants and dry conditions in sandy soil, you might need to run as long as 2 hours. Inexpensive timers are available to automate this for you.
Fertigation
Applying soluble fertilizer through the drip system is called fertigation. This is a common practice for farmers, but it is less practical for home gardeners. It requires additional equipment and is an additional complication for gardeners. Fertigation is beneficial in that it allows you to "spoon feed" your plants at frequent intervals, but home gardeners will find it much easier just to apply granular fertilizers less often.
Potential Problems
An annoying problem with drip lines laid on the surface of a garden is "snaking." When the drip tube cools down at night, it contracts. When it heats up in the sun the next day, it stretches and forms sideways loops. The loops can even push over plants. To ensure uniform watering, you then need to pull the tubing back into a straight line before each irrigation.
Burying the tube under a couple of inches of soil or using mulch will prevent this problem. When the weather is dry, your drip lines are an attractive source of water. Ants and mice like to chew holes in the tubing to get a drink. Emitter plugging is another potential problem. Particles in your water supply can lead to plugging, but plugging can also occur due to algae growth in the tubing.
Reuse of Components
Your header tube, fittings, valves, pressure reducer, filter and backflow preventer can be reused year after year. It is sometimes possible to reuse the tubing, but this will depend on wall thickness, how it is stored, whether there was ant or mouse damage, etc. Drip tubing is cheap enough that most people will find it easier to replace it each year. If you do decide to save your tubing, don’t kink it when you store it, and be sure to open the ends and flush it before reuse.