Also, do nitrogen fixers add nitrogen during the growing season? Or is it only made available after the plant is dead and decaying back into the soil? Does fixing nitrogen simply mean that the plant gets some or all of it's nitrogen from the air rather than the soil?

I have left them for now, they are still small so if the general consenus is that I should pull them, I can still do so easily. Also I do have some light mulch already down. Some beds have just grass clippings, while others have grass clippings mixed in with some dried leaves I saved from last fall (chopped up and mixed with the mower).

The grass clippings break down very fast, a nice 3 inch application is pounded down to a thin film in about a week. I get more each week from the yard, but I was hoping it would last longer. That is why I added some of the dried leaves this last time to see if it would hold up a bit longer. I only have one big bag of leaves left and they are saved for my compost bins when I add a bucket or two of veggie scraps.

If I could use this clover as a cover mulch, in some areas, I could lay the grass clippings on thicker/ more often in the rest of the garden. This fall I plan on raiding the neighbors leave piles so I have more bags stored for next year.

I'm not an expert, but my impression is that nitrogen fixers add nitrogen to the soil through out the growing season, eg the concept of the 'Three Sisters', the beans fertilizing the corn with Nitrogen. Sure seems to work for my lawn, the grass is greenest where there is the highest density of clover.

Basically, clover is good stuff.

I can't find anything good right now, but I based this on the concept of New Zealand pasture management, where a combination of earth worms, clover, and grasses combine for some of the the most productive pasture around. Right now, if I look out the window, there are at least a dozen robins hunting worms.

But then again I live in a high desert where it rarely rains, and all this is on irrigation water, a different ecosystem all together.

Only real drawback is you might need a lot more water.
I had dutch clover in a squash patch once, it seem do help a lot. I needed to cut the clover down that was right around the squash when the squash was first seeded. Once the squash got large it shaded and killed all the clover, leaving a nice mulch.

I wish the clover had lived to form a permanent living mulch.

Now water is too expensive in my dry climate, so I don't do this any more.

Thanks for the link Kimm, I will be looking into this more intentley now. Allthough the clover around here does very well, It might be beneficial to try some different varieties.