I think most of us use mulch, both for weed protection and to retain moisture. I don't really think it matters what kind you use. I don't remember what kind I got - it was the mulch of something that is very invasive and abundant in Florida (ie - eco friendly).
Good luck!

I didn't have any sort of weeds in my garden other than the occasional maple seedling that started to grow. If your getting lots of weeds, then you have a problem somewhere.

One of the benefits of the raised beds is lack of weeds.

My guess is the crabgrass came up through the bottom of the bed. Did you cover the ground with some sort of weed barrier (cardboard, newspaper, landscape fabric) before you built your beds? If you did, I'd be surprised if you got anything more than jleiwig mentioned. I've got weeds floating in and setting up shop, but they're very, very easy to remove when young and pretty rare.

Either that or your compost had crabgrass seed in it. I'm not familiar with crabgrass enough to know if that's possible. Where did you get your compost?

Sorry for all the questions, I'm just trying to get enough information to help.

Here is a link that might be useful: Sinfonian's garden adventure

Crabgrass requires sunlight for germination. Their seeds can remain viable for many years, deep within the soil. They remain dormant until the soil it turned over, exposing the seeds to 1. sunlight, 2. warmth (50 - 55 degree range for germination) and 3. moisture.

Crabgrass is also a very prolific seed producer. Proper care lawn* is the easiest way to eliminate crabgrass from your WHOLE yard. Eliminate it form your lawn - you eliminate the seeds from your garden. Eliminate sunlight, warmth and moisture of crabgrass seeds and you eliminate the germination of viable crabgrass seeds.

* Water your lawn deeply and infrequently. This allows the soil surface to dry, preventing weed seed germination. Accounting for rain, maintain 1 to 1.5 inches of water weekly. Less in cooler months - more during the heat of summer.

Maintain mowing of grass at the tallest setting of your mower. Tall grass prevents and shades the sunlight's germination of weed seeds on the soil's surface.

Never mow more than 33% of your lawns top growth. (example - when grass is 5" tall, mow to 3.5" - the tallest some mowers can go) Any shorter of a hair cut stresses the lawn too much and stunts its growth.

Feed your lawn regularly during the cooler months of spring and fall.

The above will promote a healthy and lush lawn which will simply out compete any weeds. Eliminate weeds from your lawn and you have eliminated the weeds from your garden. Proper lawn care is the single most effective way to eliminate weeds - and the cheapest too!

Prevention is also available. Preen not only makes herbicide for the garden, but they also have a pre emergent for crab grass and other grassy weeds for your lawn. The pre emergent lays a barrier on the soil's surface that prevents germination of crab grass seeds. This product is applied in early spring and timed with forsythia buds and blooms around your neighborhood.

My girlfriend below does NOT like weeds, and I oblige her!

MSMA (Monosodium Methanearsonate - http://www.maatf.com /whatis.htm ) is very effective at killing crab grass and especially dallisgrass. It is destined to be removed from the market for use by the average home owner after December 2010. Until then, you will find this product at big box stores and nurseries to eradicate your existing weed problem.

I have linked to article below

Here is a link that might be useful: MSMA agreement

I have the worst crabgrass in the world in my back yard, but what can you expect when no previous lawn care was done on the property for 1.5 yrs while it sat in forclosure/divorce of the previous couple who owned our home. All I did was lay down some weed block and put in the Mel's mix. Like I said, not one weed, just the stray maple seedling.

I put down the landscape fabric before adding the Mel's Mix. I have anywhere from 6" to 12" of mix above this (I built the bed on a slope.) I doubt the crabgrass grew up from existing soil, but perhaps I'm wrong.

The first year, weeding was just as simple as others here describe. Weeds were relatively few and far between, and were incredibly easy to pull out from the loose mix.

The second year, however, there were just far too many of them for me to keep up. And the most prominent by far was crabgrass.

I wonder if the problem is the neighbor behind me. The back of his lot is hilled up a bit, and maybe the crabgrass seeds blow down from his lot into my garden? I don't know.

My own lawn I mow about 3.5" high (to the consternation of my next door neighbor who keeps his absurdly short, and then wonders why he has to fight weeds all the time.) I also water infrequently but deeply. I overseed every couple of years with tall fescue. If I get patches, I cover the new seed with a layer of fine topsoil. So my lawn is in good shape.

Now that crabgrass has set up in my garden, I'm trying to figure out where to go from here. I'd really rather keep herbicide away from my SFG, since this is where I grow the food I eat!

Again, all advice is much appreciated!

Try putting down some cardboard over the bed, and punch holes through it to plant. Cover it with "real" mulch so it looks decent. If you get crabgrass on top of the cardboard, it should be easy enough to pull.