I'm a little confused as to why you created a cement trough to plant your vegetables in. If it's fresh cement it may be toxic to many plants for a while. Until cement is fully cured and partially eroded it tends to bleed chemicals that you don't really want in your food crops.

If you add garden soil to the trough and put in worms they'll need to be fed because they don't eat just soil, and the cement may be harsh on them too. You'll be able to tell that they don't like it if you put them in and then check on them a week later and they're all gone. Also, you didn't mention if your trough had drainage, I will assume that it does. And if your worms don't like the cement they may exit out the drain holes.

I'm sorry, I know this sounds all negative, and I don't mean to be that way, but the cement trough idea kinda throws me. Is your soil too hard, dry, rocky or toxic to plant directly in it? Cheryl

I am also confused by the idea of growing vegetables in a 8" cement trough.

yes, 8" isn't much depth, but the only "chemicals" in cement are lime and gypsum, and if they're leaching out, the concrete [which is the material you're actually making with the cement] will fall apart

adding the worms isn't a bad thing, but it's not likely to help much unless the worms are working around the plants, and they won't be much interested in sticking around unless it a very organically rich soil - also needs to be constantly moist [maybe wetter than the plants would like], and at only 8" it'll dry out pretty fast

Bill