WARNING: If you find this stuff to be absolutely boring or just too technical, you can cut to the chase and get your irrigation schedule in the IRRIGATION SCHEDULES section!
Before you schedule your irrigation, you should first review the following tips and factors:
Don’t water the same all year long. Change your irrigation schedule throughout the year. Do you honestly think a plant needs as much water in January as it does in July? Plant water needs change throughout the year due to weather and daylight length.
The best time to water is in the early morning hours to minimize evaporation and wind drift. Plus, there may be a mandated watering time frame from your local water district (Consult their website).
If you need to cut back on watering, it is in the best interest of the plants to cut back on watering days, not watering time (run time). This allows the soil to dry down between watering days. Believe it or not, unless you have bog plants, a plant’s root system needs some gaseous oxygen in addition to water.
Know your soil (See Soil chapter). Clay soils absorb water more slowly and hold the water longer than sandy soil. Therefore, if you have a clay soil, you can get away with watering a lot less days than if you have a sandy soil. However, when you do water, you will probably have to break up your watering time into several intervals to allow the water to soak in. Otherwise you will get runoff.
- Know your plants. Type of plant (desert, temperate, or tropical) and root depth affect the amount of water needed.
- Know your sprinklers. Different types of sprinklers put out water at different rates per area. This is called the precipitation rate. It is measured in inches per hour. For example, a traditional spray sprinkler nozzle has a precipitation rate of 1.5-1.6 inches per hour while a multi-stream, multi-trajectory sprinkler nozzle has a precipitation rate of 0.4-0.6 inches per hour. Think of precipitation rate as rain. If we had a rain storm dumping 1.5 inches of rain an hour, that is what a spray sprinkler nozzle puts out. Wow! That’s a lot of water! No wonder there is so much runoff in the irrigated urban world. However, it is not the sprinklers’ fault. Sprinklers need to be scheduled properly in multiple, short run times to give the water a chance to soak in.
- Know your maximum run time for each zone If you have an existing irrigation system, the best way to determine the optimal run time for each valve is to conduct a “runoff” test. In other words, turn on a valve and time how long it takes to see water starting to run off the landscape and onto non-target areas such as the sidewalk, drive-way or other hard services. Do this for every valve. If you have sloped areas or clay soils and are using spray sprinklers, this could be as little as 3-4 minutes. If you have a flat surface and sandy soils, it could be 10-12 minutes using spray sprinklers. Set your run time for one minute less than the time it takes to see runoff.
What does this tell you? Regardless of how hot it is, the maximum you can run a particular zone will always be the same. If your plants need more water, add multiple start times, about an hour apart, on the watering day.
Preparing an Irrigation Schedule
Perfection - There is no such thing as a perfect irrigation schedule. We can only estimate with the knowledge we have. Even then, plants have an innate buffering capacity. Most plants can go without water for a lot longer than you might realize. Conversely, some plants will gladly accept water beyond their needs; although this can lead to eventual problems.
Bottom line: If you don’t water perfectly, your plants will survive.
Scheduling - See the section called IRRIGATION SCHEDULES for sample scheduling guidelines for your area.