The glyphosate products are kill everything it touches material that is known to be much more persistant in the environment then the manufacturers will admit, at least according to the EPA ground water researchers who have found it in ground water. However, the glyphosates do not have long term killing affects once dry.
Now, Ma Nature would never plant a monoculture lawn as we have been doing for the last 70 years because it invites many problems. However, which types of grass to grow depends on where you are, what your soil is like, how much rain you can expect normally, etc. The USDA Plant Hardiness Zone tells us nothing except which plants will most likely survive the winter in your area.
Your state universities Cooperative Extension Service probably has a lot of the information you seek.

Sorry--my what?

Not much rain most of the time, I know that (Southern California & all). The charts I looked at said 12.94, but it does vary quite a lot year to year.

Your University of California maintains Cooperative Extension Service offices in every county of the state and can be a valuable resource for many questions gardening, farminmg, or home economics related. The link below may be of more help then the telephone books if you even have one.

Here is a link that might be useful: UC CES

Thanks!

Has anyone here tried mixing new seed into an old lawn? Any success?

try mixing new seeds with old and applying this new organic fertilizer called soifertil.they are located in south florida and are having great results with lawns...check their web site www.soilfertil.com

Could you be very specific about where your house is? SoCal has every zone and many of them climb all over the foothills as well as the valleys. SoCal soil is all over the map, too. Zone 9 isn't enough. Name the town.

Dutch white clover was one of the seeds that made the old time lawns much different than today's lawns. Now clover is a weed, but back then it was a staple of every lawn. When you sow clover seed evenly it looks very plush. When you let parts of it die or sow it unevenly, it looks clumpy and unkempt. Clover flowers also attract bees, so keep the kids and pets off of it. The other issue with clover is that it stains clothing, so don't put home base in the middle of a clover patch. The other benefit of clover is once you have it established, you never need to fertilize again. Clover seed is almost always inoculated with a bacterium which "fixes" nitrogen from the air and turns it into fertilizer for the grass.

How much are you willing to water, mow, and fertilize? Are you interested in an inexpensive organic approach to lawn care?

Oops! I just realized I was still in the organic lawn forum. So I guess you want to go organic. Nevermind about that last question.

Mixing different seed species is a very good idea, this has nothing to do with mixing old seeds with new. Just which grass seeds to consider depends on your climate and soil, things we cannot tell too much about just from "Zone 9" and southern California because there are too many differences in that area.
Having different grass species in your lawn means a healthier lawn because if one species does have a problem there are others that probably will not.

It's in Long Beach.

Also, I realize now they definitely didn't use Roundup on the lawn as that would have killed it (Told you I'm new to this lawn thing!). There is a lawn there. The front is suspiciously clear of weeds, the back has dandelions. It will probably be 3-5 years of lawn care for me before it's gone, maybe more in back since some members of the family like it.

So--looking for interesting stuff to mix in that won't make neighbors or family members unhappy.

Also, it *looks* large to me, but I think it's really more suburban-average, so butterfly meadows are out (alas!).

Climate is coastal with a 65 degree sea breeze every single day of the year. He gets early morning low clouds which burn off about 11am. Sea breeze starts promptly at 2pm.

You are actually in an area where fescue grasses and even Kentucky bluegrass can thrive. Your zone is 9 because the winter temp only rarely freezes. Most zone 9s are hot in the summer but you are not. KBG can't grow in most zone 9s but it looks excellent in your area. Some years it will be cold enough for KBG to become dormant in the winter, but that would be rare. Here are two pictures of a KBG lawn in Huntington Beach near Sunset Beach.

{{gwi:81243}}

Note from the aerial that it is the best looking color in the area. The aerial is a much more recent picture. The owner is not a lawn nut. When I took the picture he was not fertilizing at all. I suggested organics and I believe that is what he is using. He's got a great lawn with very little effort.

KGB is best planted in the fall...which is just about any time of year for you. The problem with spring seeding is that crabgrass seed is also waiting for enough water to sprout. When you apply enough water for KBG to sprout, the crabgrass will take off. However, if your KBG seed takes hold, and it will, the crabgrass will die off in the fall giving the KBG time to spread into a dense turf. Dense turf will keep the weeds out without doing anything else.

The secret to keeping weeds out of KBG is to keep it mowed at least 2.5 inches high and I would go to 3 or 4. Fertilize on Memorial Day, Labor Day, and Thanksgiving.

Thank you.