Grass roots, what would you do?

I started my SFG 2 years ago. I made the mistake of using cardboard under the bed to kill the grass/weeds. Last year, b/c the grass was coming up through the bed, I tried putting weed cloth down. But I just moved the Mel's mix from one side of the box to the other, laid down the cloth, then switched. But b/c I didn't totally empty the box, I ended up with uneven depth and the grass still came through the edges and the middle where the seam was. Yesterday, I ripped up the box entirely. What I realized was, I am missing half my Mel's mix b/c pulling the grass out took half the mix with it, and the mix is filled with roots, mostly from grass.

My question is, does grass come back if the roots are left? Should I throw away the mix, or could I use it in containers where I can manage it better. Or will it be fine to put back in the box, and just add to it?

Also, what should I do under my new beds? would weed cloth under the box be enough, or do I need to dig up the area?

Much depends on the species/variety of grass that you're dealing with. Any that send out runners or underground rhyzomes will sprout from any piece left in the ground. Those that remain "single" and reproduce only by seed may not.
As far as whether to replace the mix, someone else will need to chime in on that.

I am not sure what kind it is. Since it came in around the edge of the boxes where there were gaps, maybe it is the kind that has runners?

I understood that several layers (3-4) of cardboard would kill the weeds beneath it over time. I have had success using that technique not only beneath my boxes, but also between them (covered with mulch). I have had grass grow in from the sides into the mulch between my boxes, but not from beneath the cardboard. Bermuda grass is particularly aggressive at that, and will insert its rhizomes into any crack it can get into in the top 6 inches of soil. Once it is there, you have to get rid of all the rhizome or kill it somehow, otherwise it will return.

I'm curious: what technique did you use with your cardboard? Did you use multiple layers of overlapping cardboard that covered the entire ground surface? If the grass is bermuda, those rhizomes can even work their way through weed cloth over time (I've seen it elsewhere in my landscaping), so I'm not sure what works in that setting.

Another poster has had success pouring boiling water onto weeds to kill them. Perhaps you could pour boiling water onto your grass root contaminated Mel's Mix in small batches.

Yes, grass can come back it there are roots left, not always but it can happen.

If it is not Bermuda grass and if you plan on having a hot compost pile, you could throw that mixture of grass and roots and MM it in the compost pile. Otherwise you could just place it next to the pile, place black plastic over it for a few months to let it rot, then throw it in the compost pile.

As to the new beds, are you placing them in the same place? If so, scrape all grass and roots away down to the sub soil where there are no roots, place cardboard down, staple weed barrier to the bottom of the box, put the box in place and put in Mel's Mix.
If you are placing the beds in a new location, use a edger tool to cut and take up the sod, roots, and dirt. If you cut them into 10"-12" squares, you can place them root side up and pile them next to the compost pile. It will take a year, but that pile should become compost.

My garden boxes have lawn between the beds, so to reduce grass root infiltration into the bed, every few weeks I cut about an inch away from the outsides of the box with this edger tool.

I am dealing with the same thing. I don't know what kind of grass it is but it is extremely invasive and has roots upto 3 feet long. I put a plywood bottom on my box.

I want to scoop up the MM and put back in my box, minus the roots. Am I crazy? I hate to loose a whole box of MM. 

Someone told me to pull out all the roots and put the MM in a closed garbage can in the sun for a few months and then use the soil in the spring.


any thoughts?

Sherrie, I that idea if it works. Even my tabletops are full of crab and bermuda grasses from the lawn service mower throwing bits up high enough to get in and also this is the first year I've used my homemade compost. I think the llama and horse manure had seeds. I think I will try a bed or two. I was planning to empty some of my original beds, raise them another block high and replace the plastic liner with weedblock cloth.


Kay

Speaking from experience, it is unlikely that weed block fabric will help with Bermuda grass.

If you decide to remove the MM and start over, try putting the mix through a compost screen/sifter, to separate and remove the roots. After I do that I leave the roots out on a tarp (or a spare patio paver) for a few days 'til it's dried out --or 'til I remember it again    -- then add it to the compost. But I'm not sure just what the weed grass that grows around, under--and sometimes in my beds is.
I do also like the ideas, above, about the black plastic, and the garbage can for an extended time.