100+ degrees!?! Sounds like you need a warm season grass.

Where do you live? The zone isn't that helpful. SoCal is full of soil types as well as micro climates from mountains and wind patterns.

What is your watering schedule? How often and for how long do you water?

Why did you want clover?

There is no mix of fescue and rye that will work in SoCal unless you live west of Interstate 5 on the coast. If you don't have morning fog, a 2pm sea breeze, and high temps in the 70s all summer long, then you have no business trying to grow a cool season grass. Most of SoCal should have either St Augustine or bermuda. If you are pretty successful at caring for a lawn, then you could try zoysia. Another excellent choice for the really arid areas is UC Verde buffalo grass. Any of these grasses need water only once a week in the hottest heat of summer and more like once a month the rest of the year.

Thank you so much for your comments. I live in NE Orange County (Fullerton/Brea/Yorba Linda). I choose microclover because of the "no mow" feature and the appearance. But not being able to use herbicides on the clover I cannot control the weeds. I have had several Marathon (tall fescue) lawns which did very well elsewhere, but this neighborhood is full of Bermuda and other grass types which take over the Marathon. Since I already have microclover in the lawn, I would like to transition to another type and eventually lose the microclover. Bermuda is not good because my lawn is not graded well enough. I don't like the appearance of St Augustine. Although I've heard of them, I have never seen a Zoysia or Buffalo grass lawn. I wonder why they aren't more widely used. Any suggestions, wholeheartedly appreciated.