The garden from scratch

Water supply is coming from the burn up the hill a bit . It will run through a pipe eventually. All we’ve put in place so far is the flow through filter tank. The blue line is a ditch we dug, trying to help dry out the bottom of the plot. We’re getting it dug deeper & wider as it definitely seems to help and has constant running water. It runs into the burn that runs down the side of the plot.  I was thinking flag iris . We’ve got lots growing here. I’ll collect seeds from them this year.

Flags spread like the devil once they get established and will quickly clog up a pond or ditch. I would steer clear of them. Especially if the ditch empties into the burn. You don't want to add invasive plants to the local waterway.