Some years, we bring out the hoses and hook up the sprinklers in April; this year it's nearly June.  That said, my sun dances seem to have been working --- highs up to 90 and a week without rain has started cracking the earth as it shrinks and dries.  Garden growth is slowing down too --- thus hauling out the sprinklers.

You can read all about the reason we designed our irrigation system the way we did here.  The initial setup cost a couple of hundred bucks, but the sprinklers and hoses have been going strong for four years now without an end in sight.  I did take a minute to grease each sprinkler before getting started this spring, which should prevent the trouble I had with a couple of sprinklers getting stuck in one spot previously.  That small bit of maintenance aside, irrigation of the vegetable garden is now nearly trouble-free --- just flip a switch and change a valve every few hours.