Growing Grass.

That's a lovely idea!  I have also seen it suggested that you grow plants in trays like you said, then before you put in in with your hens you secure some chicken mesh over the top of the tray.  That way the hens can peck the growing tips but can't dig out the soil. 

When they have eaten all the fresh green shoots you can remove the tray again and let the plants re-grow before repeating the procedure.

I don't have my hens yet so of course I'm talking through a hole in my hat    But soon I will have my own flock so I will be able to try this out for myself.

Like most runs mine has no grass left in it, but is surrounded by grass, so I got some rolls of wire from Wilkinsons and  steel pins from my local hire shop, you know the type that look like a shepherds crook, and just make a temporary run from the coop to the grass, I move the fencing around after a couple of days so they don't demolish the grass totally.  Take your point about growing it in pots though. alison