Parts of the garden that will be watered together are called zones. Divide your garden into zones first based on what plants can be watered together. Containers and hanging baskets should be on their own zone; they get watered more frequently and for shorter times than plants in the ground. Vegetable gardens, because of their seasonal nature, are best operated as separate zones. Misters, which come on several times a day, should be on their own zone. Micro-sprinklers, which used much more water than other emitters, should have their own zone. Almost everything else in the garden — trees, shrubs, groundcovers, and flowers — can share zones.
Another reason to divide the garden into zones is to be sure each zone has enough water to service all its emitters. In a small garden, this can probably be ignored — hundreds of emitters can be put on a single line — but large gardens need some calculations. If your garden is very large or if you are including many micro-sprinklers, count the emitters needed and the line lengths for each zone. If the required flow rate for a zone exceeds that available, divide it into more zones.
If your garden is on distinctly different elevations, either use pressure-compensating emitters or plan separate zones for each elevation. Non-pressure-compensating emitters need to be close to the same elevation as other emitters in that zone.
Because of flow loss due to friction, don’t plan more than 200 feet of plain poly pipe or porous pipe in a single zone.
The maximum length of pressure-compensating emitter line per zone depends on the spacing of the emitters and their flow rate, but can range from 326 feet for 1/2 gph emitter line on 12-inch centers to 248 feet for 1 gph emitter line on 12-inch centers.
As the spacing increases, so does the length of emitter line that can be used. For emitter line on 24-inch centers, the usable length per zone jumps to 584 feet for 1/2 gph emitter line and 444 feet for 1/2 gph emitter line. These numbers may vary. Consult the manufacturer’s recommendations. Use much shorter lengths of 1/4-inch vinyl tubing.
Number of Emitters
Like line length, the total gallonage per zone is limited by the available flow rate (see Planning Drip Systems). Add together the gph used by each emitter in a zone. The total should be within the available flow rate. There is plenty of leeway.
For example, if your available flow rate is 150 gph, you could use up to 300 1/2 gph emitters (300 x 1/2), 150 1 gph emitters (150 x 1), or 75 2 gph emitters (75 x 2) per zone.
The water use of micro-sprinklers resembles that of sprinklers more than that of other emitters. They should be on a separate zone from other drip irrigation devices because of their greater water use. The flow rate of a micro-sprinkler varies from 7 to 25 gph, compared to only 1/2 to 2 gph for most emitters. Therefore, you cannot use as many micro-sprinklers per zone as emitters and you probably will have to divide large micro-sprinkler zones into more than one zone. Take these factors into account in laying out micro-sprinklers:
The radius of a micro-sprinkler, like that of a high-pressure sprinkler, should always overlap its neighbor’s. Since there is little wind drift, the minimum overlap is only 25 percent of the diameter. Many micro-sprinklers require a minimum water pressure of 20 or 25 psi. Don’t use more than 150 feet of 1/2-inch poly pipe per zone. Use no more than 5 feet of 1/4-inch vinyl tubing between the 1/2-inch supply pipe and a full-circle sprinkler, or 10 feet for half-circle, quarter-circle, or strip sprinklers.
Micro-sprinklers vary in flow rates, so check the manufacturer’s specifications. For example, one manufacturer rates its full-circle micro-sprinklers at 25 gph, its half circles at 14 gph, and its quarter circles at 7 gph.