Pickerel weed is available at garden centres in pots suitable for planting in ponds. They will spread slowly.

Unless you own the ditch, it is illegal to take the plants.

Well I'm a bad boy. It grows in ditches here also. I've never seen it in local stores...we live in a fairly small town. I dug one up. It was one of THOUSANDS growing everywhere. I have it potted, growing in my pond. It did very well. It's getting bigger and bigger and blooming. I think they are very easy to transplant. If they are very common where you live, I see no problem in digging one or two up. The only problem is you might introduce some unwanted critters in your pond. It might be illegal to gather plants in your state. To be sure, you could call your local county or state fish and wildlife people, or you could do what this baaaaaad boy did and just go dig one up.
-Burt

We have some growing in a boggy area created when riprap (bulkheading with limestone) was put on the riverfront. The filter cloth and the gabion cages filled with limestone rock blocked the water drainage somewhat, and it backed up to create a bog. It is right in front of my house, on the grounds of property owned by friends. Today we were out removing seedling chinese tallow trees (popcorn trees) and leaving the good bog plants. We were also shopping for mallow and other plants to populate this lovely little wetlands garden with. The pickerel as well as plantain lilies look good here. All kinds of frogs serenade us in the evening also.

One reason I'm online now and reading this thread is to find out some other good bog plants, especially native species. My new home is not far from the one I named Moccasin Landing, and sold in mid May.

I'm in zone 8 & also have a natural Bog area that is a runoff from a creek on the property. I've planted Spider Lilies,Cardinal Flower,Lizard's Tail & Iris.I've enjoyed it so much that I put a door from my bedroom going to a 10 x 10 deck, put an old statelite dish in the ground & made a pond,and am creating my own litte Bog "right outside my door"! I do love those frog serenades!

I think many people fail to realize that,in the south,our rural ditches have many interesting plants in them and along them....which are frequently either dug out or worse, sprayed with herbicide, by the County or State. A plant taken home from a ditch full,is actualy more of a rescue!The main problem I can think of is bringing home unwanted pests, parasites and weeds.