Can I reuse grassy soil in a new raised bed if I tarp it to kill the grass within it?

I succeeded in convincing my mom into getting rid of her useless unkept lawn (thin crabgrass, dandelions) last summer (zone 8b). I essentially scalped the entire lawn with a shovel, removing anywhere from a 1-4 inches of the soil/grass, and mulching the area with woodchips. That soil/grass has been sitting in a heap in the corner of the driveway ever since.

In the fall, we extended a small raised bed of hers that sits on the side of a slope using retinaing wall blocks. The original bed had good soil (tomatoes, strawberries in it last year), but we need to now add additional soil to help fill it so we can replant veggies this spring. Currently the bed is mulched with a thick bed of leaves and coffee husks.

I was thinking that I could use the soil that I removed last summer, even though it still has plenty of grass and weeds in it, if I fill the bed with it and mulch it like crazy to kill off any weeds. Does this seem like it'll work? What should I mulch it with and for how long? Would clear plastic tarp be more effective than a natural mulch since I assume the only way to kill the seeds is for the temperature to reach 130F? Doing my best to try to save money by reusing this soil.

Thanks.

Hello Kev,

It can be done but it will take more than one season to kill-off the grass and weeds, otherwise you risk ongoing infestation in the garden bed = a royal pain in the arse.

I had a garden bed infested with Couch (Bermuda Grass), after years of fighting it, decided to cover the bed with chook manure and lime, water well, then cover with black builders plastic - just let it sit for two years and voila, no more grass but richer soil.

Perhaps better to compost it separately, that way you make sure they're all gone and end up with a richer product.

Good luck.

Agreed -- if you could make a big hot compost pile and put that grass into it, perhaps you might kill the crab grass that way.  But it's really really tough to kill.  

The other concern is that buried green stuff tends to produce methane—something that will not be good for anything growing above it.  So if at all possible, compost it.  

One thought would be a big compost tumbler.  You could keep piling the green stuff in, feeding it daily with your kitchen scraps and such, as well as clumps of that grass.  Give it a couple of turns, and tomorrow add more . . .  over the course of several weeks, you should be able to compost all that grass.  They key would then be to sift it out as it's finished, but don't let any crab grass roots escape.