Toss some nitrogen in that plot.
I've planted cereal grains 2 or 3 weeks after using clethodim. Killed the grass portion of what I wanted, but left the sedge behind. Kills perennial rye without bothering my tree plantings. Pretty sure it kills crabgrass too. The issue with clethodim, is the give the non-target plants preference. So, other undesirable weeds that clethodim doesn't touch gets bumped up. Weather when I used clethodim has been decently warm, so I can't tell you about early or late season results.
I wouldn't hesitate to spray clethodim 2 weeks before planting, then spray gly when planting buckwheat and some clover. I would put some nitrogen fertilizer on the plot 3 weeks after planting if possible, or while planting. Actually, spread that fertilizer when you put clethodim down. They say waking up the plant when you spray is good.
Clethodim is slow to see results, unlike gly. And it often takes more than one application. Folks have sprayed cleth and gly at the same time on here with ok results.
With any target weed you want gone, know what your dealing with. ID the plant. Some pictures of the plot with the main 2 or 3 weed closeups would be helpful.
Clethodim is basically an oil, so you need a decent amount of surfactant mixed with it. It also has residual smell. It's not that horrible. It reminds me of my childhood because they use that stuff in vineyards alot.
