Companions for daikon?

I have two new hugelkultur-ish beds that I began establishing last year and this year I'd like to plant daikon radish in them. My purpose is not to harvest them but to leave them in the ground to decompose. I'd like to know what might grow successfully alongside the daikon, also not for harvesting necessarily, but more to chop and drop. Could I do buckwheat grass at the same time, for example? Any other ideas? I live on the south shore of Nova Scotia in Zone 5a/b.

I've seen a row of daikon with salad mix on both sides and everything seemed to be doing good. daikon kim chee so good for you
edit*this was in a groundlevel bed that had been tilled

I did exactly this but put oats in with them, since I used manure too, I thought I'd put in a nitrogen scavenger. One bed went perfect, one went so-so, and the other didn't go at all. It was all in the timing, methinks.

The best advice I can give is to be careful when you plant daikons. They're like beets and temperature/sunlight/spacing really matter. They may go to seed if the soil temp isn't low enough. Too early or too late and you have bolting or not germinating. There are threads about daikons here.

best,
William