Wendy Blackwell wrote:the real question to ask is "why does the crab grass grow?" the following link reveals some clues. http://www.sierra-worm-compost.com/soil-fertility.html
weeds are pioneers of disturbed land. Indicators of soil quality, deficiencies, and excesses. crab grass grows in dry, compacted, low fertility, low calcium soil. fix those problems, and your cg problem will lessen.
I have a 1/4 acre in Sonoma County. 1/8th of my plot is a weed patch. wild carrot, wild radish, daikon I introduced, prickly sow thistle, bind weed, frog fruit, crab grass...more nameless weeds than I can identify. I mow my weed patch once a month, starting in spring and by now, late july, its still green and growing, yet I do not water my weed patch. Everywhere else the ground is dry, cracked, dusty and sad. My thought is to return the nutrients that the weeds are pulling from the earth, back into the soil, and let them do the hard dirty work of breaking up the clay. I've turned my weeds into a living mulch and tiller. In the winter I run the chickens in the weed yard, so I can sow the orchard (where they spend their summers) with ryes, legumes, and chicken forage and let them decimate Weedlandia, and in the spring, before the last rains I seed the weed yard with whatever I want. its usually a mix of green manures, soil busters, legumes, beneficial incest blends, wild flowers, and any extra seeds I might have lying around. This is my second summer of this plan, and the soil is already improving, and some of my seeded plants are taking root.
in permaculture we don't see problems, we see solutions. Turn your weed "problem" into a solution, and remember, slow and steady wins the race.
also, if you must have a garden to tend while you remediate your soil, lasagna garden a small space intensively, that way if you have to weed, or pile on more and more mulch/manure/cardboard/mulchmanurecardboard, at least its on a small space, while you work on the bigger projects slower.
I know my reply wasn't about destroying crab grass, but maybe destroying it isn't the answer.