I live in PA, and don't know anything about California lawns, but I wouldn't normally expect clover to appear as tiny leaves all over a new lawn, especially at this time of year. On this side of the country, I'd wonder if what you're seeing is one of the winter weeds, like chickweed or henbit, which often arise in new lawns that haven't filled in yet.

Can you post a close-up pic?

Identification is the first step, but to answer your question, I'd expect that using a broad-leaf herbicide this soon on your new lawn would indeed stunt or kill at least some of the new growth.

Since you've been there a year, do you remember what its flowers looked like? Clover has white or very-light-purple flowers, and isn't overly aggressive. Oxalis looks like clover leaves, but has tiny yellow flowers and can be very aggressive.

Why would yuou kill the other 50% to deal with crab? That was not the best move. Crabgrass is very easy to control. for that small a lot, I would call someone since most OTC stuff does not work. I like Drive 75 for new lawns but that is my world, not CA.

Thanks to you all for the various responses. I'll try to get some good photos to post. As to the Clover vs. Oxalis question, I think that may be part of the problem. At my previous house we had a horrible Oxalis problem, which I eventually controlled only by adding 18" of new soil when terracing the yard. That variety had a four-lobed leaf and yellow flowers on a long stem.

This "clover" as I called it is different. It is low growing, with a 3-lobed leaf, and I've seen small yellow flowers as well. This stuff pops up all over the yard is small amounts, and I've been either pulling or killing with glycophosphate. I haven't found the small bulbs in the ground that I found with my previous experiences with Oxalis.

Also, to buy_25: You're right, I tried all the OTC stuff and couldn't kill the crabgrass. After trying that and pulling as much as possible I just came to the realization that the old lawn had maybe dozens of different grasses, some healthy some not, and it was nearly impossible to tell what was crabgrass and what wasn't after a while. Here in CA the lawn never goes dormant, so preemergent crabgrass killers just don't seem to work. Everyone I called around here just wanted to put in new sod...

If it's low growing with yellow flowers, it may be black medic. If it goes to seed, do the seeds look kind of like tiny grape clusters?

I like clover and even planted some on purpose, but I dislike black medic. It can spread out and choke out the grass as it spreads. I find that if I let the grass grow fairly tall and water deeply and infrequently, the black medic doesn't have much of a chance to establish. What does pop up, I pull by hand or with a weed hound.

Ken:

Most of the "clover-like" weeds that have been mentioned can be pretty easily controlled with Triclopyr, which can be found in Ortho Chickweed, Oxalis and Clover Killer, and also in at least one of the Bayer Advanced products. It may take a couple of treatments, but they do work. I'm not sure that they're OK for use in California - you'll have to check.

Good luck!

bpgreen and Andy may have put me on the right track! The major weed isn't black medic, but reseaching it took me to Yellow Woodsorrel and Creeping Yellow Woodsorrel. (Each a variety of Oxalis.) I think I have the creeping variety, which according to UC Davis tends to germinate about now. I've added a link with pictures. As with most things here, it grows all year round. (We rarely get below 40 in the winter or above 90 in the summer, but have lots of cool coastal fog.)

The third and fourth pictures are of another weed that was agressively taking over my back yard and seemed invulnerable to all but roundup. I'm seeing a few sprigs of this pop up again too. Any ideas of what it is? (or how to control it?)

Andy--the idea of Scott's Oxalis and Clover Killer was a revelation to me. It isn't carried at any of the local garden centers, and I've asked several of them for advice on killing oxalis at my previous home. I was able to find it online however and hope to get some. I assume I'll have to wait another month or so for the lawn to establish.

Thanks again to all for your help!

Here is a link that might be useful: Unidentified weeds

You surely have oxalis --- it will bloom yellow & it's about the biggest pest known here in the SF Bay.

Unless you want to completely start over again you will probably just have to live with it this year. The only options for destroying it in lawns usually cannot be used on newly seeded lawns.

Trust me when I say spraying an appropriate herbicide is your only hope. I have lived with oxalis for 30 years -- even in open ground it cannot be successfully pulled. There are a thousand little bulbs, some almost microscopic, that break off.

Ortho 'Weed-B-Gon' now has a version for killing oxalis and crabgrass in established lawns. Be patient. It takes a while but it does a pretty good job over time. Mix it to the exact directions: too strong might damage the lawn and it also can "burn" the oxalis so you lose the systemic benefits of it killing the roots. It will take days if not a week or more for the oxalis to show signs of dying back, depending on the weather, but it WILL work.

You will probably be dealing with this over several seasons. Patience pays off with oxalis. Oh -- if your neighbors have it, you will get it again. It's very invasive in the Bay Area. Your popularity in the neighborhood may plummet if you've just sprouted a whole front yard full of the stuff.

Jsut saying Oxalis is very easy to get rid of but If you are using Ortho, good luck. I know I can kill it within 5 days with chemicals.

My brother-in-law tried Weed-b-gon (2 bottles) to get rid of clover. I told him throw it in the trash. 1-month later, he asked for help. Momentum FX2, gone in 4 days.

If the clover/oxalis/crabgrass is still actively growing, you do have options this year. Quicksilver or Octane herbicides will burn it down. Combine with Drive 75 and you will get a really nice kill. Look for your nearest John Deere Landscapes store and buy a bottle of each. It will be worth the money. The problem with triclopyr, momentum fx, etc., is that they can harm new grass. The general rule is not to apply those herbicides until you've mowed the new grass 3 times or more. Quicksilver, Octane, and Drive 75 or XLR8 will not hurt new fescue. The quicksilver or octane will attack the broadleaf weeds while the drive will attack both broadleaf and annual grassy weeds. You will most likely have a problem for the next few years, so spending $200 on a couple bottles of chemical will be well worth it. Good luck.

Drive 75 is about $80 per lb. Lesco/JD is well over that..Look around before going there.

In fact, skip JD and look elsewhere. Price are too high.

I just bought the same dwarf bonsai tall fescue mix by Stover to plant in my San Francisco cold and foggy Richmond district coastal lawn. How is the grass doing? Do you recommend it? Someone else recommended eco-lawn, but its so expensive. Thanks