Sprinkler coverage problems

Now that we are entering the final stretch of summer you should have a good idea of what your irrigation system's weak spots are and where coverage is lacking.  If your system was designed properly & built properly so flow does not exceed supply and we have head to head coverage this shouldn't be an issue.  However, landscapes change over time with plants maturing and sod/beds changing shape; heads can get blocked or be in the wrong place. 

The first thing I do when evaluating a system that is new to me is to run through each zone and make quick arc adjustments to heads, flag out heads that need to be straightened, that are clogged or need to be raised.  This is much like the spring start up process and can vastly improve coverage in lawn areas.  These are things that you, the homeowner, can easily accomplish on your own while also getting to know your system better.  All you need are a pair of channel lock pliers, a shovel and a willingness to stand in the sprinklers on a hot day!  For more information on how to do these adjustments, please check out my two earlier blog entries on basic sprinkler system maintenance.  I also keep an eye out for heads that may be buried in bushes and either prune them back or move the heads out from under them so the spray pattern is less affected.

Sprinkler coverage can also be lacking due to poor design or installation practices.  The way this is usually characterized are by brown arcs or spots in turf or plants that aren't getting sufficient water in beds areas.  Proper irrigation design dictates that head to head coverage is necessary for even coverage; this means each head should be hitting the adjacent head.  Coverage that falls short will usually show in brown areas that, even if they are getting hit, are not getting adequate amounts of water.

Coverage issues that are due to insufficient flow, pressure or head spacing is a little more difficult to resolve. Usually if you can push a head that's running back down into it's body with your hand, the pressure is too low.  Most spray nozzles are designed to run at 30 psi and most rotor heads are designed to run at 45 psi, if you can easily push the head down with your hand the operating pressure is less than 20 psi.  What this likely means is that your head is not spraying as far as it should (ie a 15 foot nozzle may only reach 11-12 feet) and spray patterns within that arc may not be uniform.  This pattern of non-uniform spray distribution is common with rotor heads and what you will see here is a doughnut or bulls-eye pattern of green grass several feet out from the head with brown grass in between.  Resolving these issues is getting into an area where a lot more skill and experience is necessary.  Steps such as renozzling heads, moving or adding heads or splitting zones up may be necessary to improve the coverage.