Setting the times for your sprinklers should be a simple matter but rarely is. To avoid many of the simplest problems, a basic knowledge of your system is a necessary first step. The second step is knowing the factors affecting your choice of how long to water. For the first step knowing what type of sprinklers each zone has is a must. Are they fixed spray heads, low volume streamers or pop-up rotors. Since each of these types have different outputs, this affects the amount of time needed for an individual zone. The next thing to look at is the timer it's self. For the best results the timer should have the option of between two and four programs, each with multiple start times. This will give you the flexibility to water each zone according to it's individual needs. The second step is knowing the factors that affect each zone. Is the zone grass, established planter bed, annual flowers or a mix of these. Also knowing the type of ground will help in your choice of times. Sun or shade as well as the slope of the ground will also affect how much water an area needs and how it's applied. Soil types have a great deal to do with the way you apply water to each zone. Clay based soils especially need a method called cycle and soak. What this means is shorter times with multiple starts to allow the water to be absorbed. Areas with extensive slopes will also benefit from this watering method.
Another thing that can help decrease the watering time needed is sufficient fertilizer. What I have found is that a good slow release fertilizer will cut the water needed for your grass by at least one third. Using a winter fertilizer at one and a half times the normal rate will extend the time before you need to turn your system on in spring. Some information that will help is knowing the precipitation rates of the various type of heads in common use. Spray heads average 1.5 inches per hour with a flow rate of 3.5 GPM. and rotors will average .70 inches per hour with a flow rate of 8.5 GPM. Low flow streamers such as MP rotators will fall about midway between these two extremes. In the case of rotors you need to know what size they are, half inch, three quarter or larger. The most common for residential use are half and three quarter inch heads such as the rain bird 3500 and 5000 series. The reason this makes a difference is while the precipitation rates are about the same the flow rate for a half inch head is a little over half of what the three quarter head is. The example given above is for a three quarter head.
For most of my life I have heard it said that grass only needs one inch of water per week. Now this may sound reasonable but in all my years in landscaping I have found that this only applies to ideal conditions which we all know is rarely the case. In those cases where an upgrade to your timer becomes necessary, two of the most reliable that I have found are the Rain Bird ESP series and the Hunter Pro-C, both of which are good residential timers.
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