As a rule of thumb, most vegetables need about one inch of water per week. Whether you are a commercial grower with hundreds of acres or a homeowner with a small backyard garden, how efficiently you get that water to them will influence your success---or failure. It makes sense that vegetables need more water in hot, dry weather, but whether to use overhead sprinklers or drip irrigation is less obvious.
A sprinkler on the end of a long hose has one major advantage---it can be placed anywhere that water is needed. It can be left running for as long as you want, and if its spread is adjustable you can water only the area that needs it. On the other hand, because it waters only one area at a time, you have to keep track of it and move it at regular intervals.
Drip irrigation uses lengths of lightweight hose fitted with emitters---tiny valves that release precise amounts of water in a steady drip-drip-drip rhythm. Because each drip emitter covers only a few inches of soil, you need to decide in advance which areas will get water. This is fairly easy with vegetables grown in long rows. Each row gets its own drip line. You can even place each transplant next to an emitter for maximum efficiency.
Overhead sprinkler irrigation wastes a lot of water. On a warm summer day, as much as 80 percent of the water from a sprinkler system is lost to evaporation. It never reaches plant roots. Drip irrigation, however, wastes hardly any water at all. The steady drip-drip-drip places water right next to the plant so it can immediately penetrate the soil surface and reach the roots. This encourages deep watering so that plants build large, vigorous root systems.
Plants don't like getting their leaves wet. They need water only around their roots. Leaves that remain wet---especially overnight---are perfect breeding grounds for all kinds of plant diseases. This is particularly true for the squash family, including cucumbers, melons and zucchini, which are very susceptible to leaf mildew diseases. Sprinkler systems create moist environments that favor diseases, while drip irrigation puts water where plants need it, only around their roots.
Working While Watering
For the grower, a great advantage of a drip irrigation system is that you can work in the garden while it is being watered. Also, if individual drip lines are fitted with shut-off valves, you can give one row more water than another---lettuce likes more water than lavender, for example---so you can turn a row's water off while you weed around the plants.
Setting Up a Drip System
Plan a system with a simple sketch, then order the components. Installation of most drip systems requires only a pair of scissors, a tubing cutter and a screwdriver. Connections can be joined and taken apart easily, so changes can be made at any time. You MUST include a back-flow preventer at the faucet connection, and if you use well water you should fit a mesh filter in the line to prevent the emitters from becoming blocked.