Plants for Duck Pen?

I had good luck with mim clover, crimson annual clover and a northeast usa cover crop blend in my duck area. It was fill dirt before it was turned into a duck area so there wasn't any greenery. do have bare spots this year but I don't think the ducks caused those.

I'm over planting with sorghum grass (which loves muddy and wet conditions) and a northeast forage mix for livestock. Sorghum grass can grow very tall.

Other plants i know my ducks enjoy eating: watercress, dandelions, those cornflower blue flowering plants (i'm having a brain fart and I don't remember what its actual name is), dock, sorrell, thistle, chick weed, mint... I'm sure there are others.

To avoid a nasty and yucky pen/aviary:

#1 I would give a much bigger space to the ducks.
#2 the wet ground problem (which happens in any aviary and pen no matter the size) cannot be 100% solved, but it can be helped. Some bushes and small trees absorb a lot of water. A Cedar sapling that you, cut and manipulate it into a bush will absorb alot of water. Also you can google plants that help control wet spots and you'll find some plants. I think pampas grass it good as well, but be sure to the variety of pampas grass that is not sharp and would not hurt the ducks if they accidently ate it. Willow trees are also very good at absorbing water.
#3 Around any water source I would make a small drain system or even a ditch type thing where the water can be lead out of the enclosure.
#4 If you do supply a pool (which I suggest any duck owner doing) be sure that it is a stable pool (like dug into the ground.), or that if you use a trough that it comes with a drain that you can empty the water into the ditch system or that you can put a hose on and have the water flow out. If you have to dump the pool i suggest trying to take it out of the enclosure.

I may have missed it if someone else pointed this out, but....

When setting up the pen, make sure the whole pen is on about a 2 to 3% slope, with a shallow channel at the downhill side to direct water into a garden area of some sort.

Our pen is not a nasty mess. We have a base of compost made from chopped straw, leaves, and duck manure. Under the swim pans we have a mix of sand, smooth pea gravel, and oak leaves (greatly reduce odors in hot weather). That area gets a bit mucky and needs to be raked a couple times a year, and refreshed with sand and/or gravel.

You can grow some vines in or near the pen. At first, you'll need to protect the vines' base with fencing till they mature - as someone wrote above, woody-stemmed perennials can withstand some duck attention. We have hardy kiwi in the extended pen area, and I have read that the leaves of the hardy kiwi are just fine for ducks to eat. Mulberry leaves are also edible.

I sometimes grow wheat seeds into fodder and the ducks love that. I also grow "chicken salad," which is a mix of cole seeds (cabbage, turnip, broccoli, etc) for feeding when they are an inch or two tall. I grow them in a plant pot and set the whole pot into the pen.