I like a semi-natural lawn: turf grass, but with some wildflowers encouraged.

After a few years of seeding, I finally have large patches of white clover established in my lawn, in thin topsoil over glacial sand - very dry! It's slowly spreading in some areas, and I'm hoping will fill in the barest places where grass just won't grow. (I mulch-mow, but don't water as a rule.)

I've been mowing a couple of times in the spring, then waiting to cut again until about July. This lets my favorite wildflowers go to seed; then I have a mostly-grass lawn again through autumn.

Clover seed is expensive. It also seems that letting it naturalize should encourage the hardiest strains for this plot. So here's the question: how long after flowers go brown does it take for seeds to ripen? I've never actually seen seed on the plants; I guess it falls/blows out as soon as it's ripe.

I've read that the flowers wilt as soon as they've been fertilized. Is there some fixed number of days after that until I can mow without losing all the seed?

Thanks-

Chelydra