Crabgrass in your turf getting you down? I get questions about this all the time, and there are a couple of different answers. First you must know that I hate turf, period. If I didn't think there would be a riot in our cul de sac I'd rip our entire lawn out. Okay I'd leave a little bit of grass for the dog and the kids to run around, but overall I think Americans are way too obsessed with having the perfect lawn. Personally crabgrass doesn't bother me but I know that it bothers many of you (including my dad who obsessively picks it every time he is here.)
There is one simple thing that you can do to significantly reduce the amount of weeds in your turf. It's completely organic, and may even make your life a little easier. Let your grass grow a little longer or mow it higher. Most turf weed seeds need sunlight to germinate, so if you are cutting your grass too short, especially during the hot days of summer when the grass is barely growing, you are setting the perfect stage for crabgrass. I'm including a link from the University of Minnesota Extension service as they explain how to mow much better that I can.
Corn gluten meal persists as the most effective organic herbicide. The most important thing to note is that corn gluten only works on annual weeds (so not dandelions) and must be put down on the lawn at the correct time for several years before it is really an effective means of weed control. More about corn gluten application here. I have not tried corn gluten personally, as I'm afraid that the dog will eat it (he's not too smart.)
This time of year is also perfect for overseeding. I need to get on that pronto. And then don't mow for a few weeks after, give it some time to grow in nice and thick and choke out the weeds.