Ditto what bonsaikc says, Jay.  I fight drought and high heat all summer long down here in the Deep South, and without a misting system and timer that makes it come on to both cool and water, your trees won't stand much of a chance.  I've found that any fear of overwatering is unfounded when using a mist system (versus say deluging during the day, and drip systems can fail if the soil goes alkaline and you get channeling).  The trees grow a lot better, and you don't have to rush home to find wilted leaves, drench the tree, recover by morning, then repeat the process.  This kills your trees sooner or later, I know because I've done it.

Very nice elm you've got going on, by the way.  You've done an excellent job developing it.

Zach