A drip irrigation system can be as simple as a length of drip tape connected to a garden hose. However, a garden that has a range of plantings---shrubs, bushes, trees, large and small perennials, plus annual flowers and vegetables---needs a more controlled and flexible system that fits the needs of different plants. Controls include a variety of emitters, separate zones, automatic timers, and shut-off valves for individual lines.
Group Your Plants
Start by separating your plantings into groups, regardless of their location in your garden: mature trees, perennials, annuals and so on. Each may require a different type of emitter. A full-size tree will appreciate a ring of emitters in a circle around the trunk. A shrub or large perennial may need a mini-sprinkler that is hooked into the drip line but which provides more water over a larger area. Annuals do well with regular in-line emitters, but you need to decide on the emitter spacing---6, 12, 18, or 24 inches.
A large garden may require two or more zones. Even though drip systems are economical with water, irrigating a large garden with one zone may overtax your water supply. Different zones allow you to stagger watering to maintain pressure.
Separate irrigation zones can take account of naturally dry or wet areas. A rock garden, or a line of hanging plants, can also be put on a separate zone so that watering can be tailored to their specific requirements.
When to Water
Timing is an important consideration. A standard fruit tree needs long, deep watering perhaps once or twice a week, while a vegetable garden will want water, for a shorter period, every day to two. A border with a mixture of shrubs, large and small perennials, and annuals might require two separate systems---one for the annuals and small perennials, and one for the rest.
Make a Sketch
Now prepare a sketch, roughly to scale. Use colored markers to indicate where the various types of plants are located. See if you can link, say, all the trees with one line. If you have large borders separated by lawn, you may need to put each border in a separate zone.
If plants with dissimilar water needs are in the same area, consider installing shut-off valves on some lines so that you do not over-water some plants while giving others what they need.
Automatic timers can take care of complex watering schedules, but should be checked frequently. A timer that sticks in the on position, or which fails to turn on at all, can quickly cause a lot of problems. A lawn can usually handle an irrigation mishap for a while without too much of a problem, but a flower border or vegetable garden can soon suffer permanent damage from too much or too little water.
Working with a Consultant
Companies that install irrigation systems, and some online retailers, will offer advice and consultation on overall design and layout, and choice of drip fixtures. Few tools are required for a do-it-yourself job--usually a tubing cutter, a hole punch, a pair of scissors, and a screwdriver are all that is needed. Finally, most drip systems can be modified fairly easily, so you will not find yourself locked forever into one layout. As your garden changes, the drip irrigation system can be adjusted to match.