Watering your garden by hand can be a wonderful leisure activity. However, when life takes over and you don't have time to get out there for a week or two, the plants start to suffer. Drip irrigation saves time, conserves water and can be surprisingly fun to install. There's some planning and work involved at the outset, but after a drip system is set up, the entire landscape is watered automatically. One of the first things to understand before attempting to install a drip system is the different types of drip emitters -- the little pieces of plastic that deliver a precise quantity of water to your plants.
Drip Emitter Basics
Drip emitters release varying amounts of water, so you can give each plant exactly what it needs. There is no exact formula to determine how much water to give each individual plant, but all other things being equal, the bigger the plant and the greater the surface area of leaves, the more water it will consume. However, succulents and other plants from arid regions naturally have much lower water requirements than a similar size plant that grow naturally in damp conditions. The variations in drip emitters make it easy to irrigate different types of plants with flexibility and precision.
Use 1/2-gallon-per-hour emitters for small flowering perennials. One-gallon-per-hour emitters are appropriate for shrubs, although you might need to install several to cover the root zones of larger, well-established shrubs. Two-gallon-per-hour emitters are typically used on small trees, but numerous emitters will be needed around the base of each tree, depending on its size and water requirements. Remember that all plants on a single drip-line will get water for the same amount of time, so using emitters with different outputs is a way to get more water to the plants that need it and avoid drowning plants with low water requirements.
To make things easier when you want to evenly saturate an entire area, you can use tubing with the emitters already embedded in it. For example, this is useful around large trees where the entire root zone needs to be irrigated, not just a few individual points. It is also the best way to irrigate beds of annual vegetables or flowers. These plants are spaced so closely together that it is easier to saturate the whole area, rather than trying to install one emitter at each plant. However, in-line drip emitters are spaced either 6 inches or 12 inches apart, which means the emitters will line up perfectly with plants that use the same spacing.
When you go shopping for irrigation supplies, you may notice that some drip emitters are labeled as "pressure-compensating." The idea is that no matter what the water pressure is in the drip system, they will emit the same amount of water. This is important, but it only comes into play when irrigating on a slope, since all drip emitters behave this way on flat ground. Where the terrain slopes uphill from the source of the water, the emitters at the highest point will emit less water than those lower down. Since "pressure compensating" emitters cost more, don't bother buying them unless the area covered by your drip system varies by more than 5 feet in elevation.