I moved into a new place a few months ago. When I moved in, the entire yard and garden area was covered with tall dead yellow wheat looking weeds. From what i hear the last tenants (who ignored the yard for a few years) covered the yard in weed killer a few months before I got here. Anyhow, I dug the whole yard out (these weed things were hard and deep) and removed everything from the yard, leaving a clean dirt yard.
I built a few garden boxes and planted a few plants in the yard. I mixed the native soil with some garden amender, mulch, and fertilizer. After a good rain and a week or so of watering the newly planted areas, grass looking sprouts started coming up everywhere. When I pulled them out, it looked like the grass blades were growing out of these spikey wheat looking pods.
These pods and the grasses that are sprouting from them are pretty much everywhere. Even in little pots where I mixed some mulch with the native soil I'm getting like ten to twenty blades of this stuff coming up.
My questions are:
1. Can I ever fix this soil to make it useable? My feelings are that if these pods can live through poison and being cut down and come back to life six months later, what is ever going to get them out of the soil for good?
2. Should I scrap my garden boxes and start over with soil from somewhere else?
Don't worry, you can get things under control. This is the time of year when all the weedy annual grasses start to sprout, so what you're seeing now are sprouts from seeds that were already in the soil. The weedkiller that the previous residents sprayed would have only killed the green growth from last year's plants, it wouldn't have any effect on the seeds that were in the soil. And even though you dug out some of the soil, there still would have been seeds buried in the soil that was left.
For the plants that have already sprouted, you'll have to pull them, mow them, poison them (whichever method you prefer), then since there are undoubtedly still some seeds in the soil that haven't sprouted yet, get yourself some pre-emergent herbicide and apply liberally. You'll need to continue to reapply it periodically throughout the winter months (there should be directions on the package about how often to do it). The catch with pre-emergent herbicides though is that they stop all seeds from sprouting (not just the weeds) so if you were planning on trying to start your plants from seed then this approach won't work. But pre-emergent won't have any affect on plants so you can buy plants and plant them and they'll be fine.
The bad news is that these seeds blow in from everywhere, so chances are there's a weedy field (or neighbor's yard that isn't kept up) nearby that will provide a new supply of seeds for next year, so you'll have to do the pre-emergent thing again every year (or hand-pull/spray stuff that pops up). But I've found if I keep up on weeding & pre-emergent things don't get as bad in subsequent years, but you do have to stay on top of things.
For your little containers--garden soil is not good to use in containers so I'd take it out and use potting mix instead (nothing to do with the weed seeds, garden soil doesn't drain well enough to be used in containers). Same thing for your "garden boxes" if they're containers, but if they're raised beds not containers then the garden soil would be fine.