Answer: This is a very difficult question to address without seeing the site. Often, plants are not the whole solution to a wash out problem. If the sides are very steep, planting probably will not hold it in place and the plants will wash out before they even have a chance to take hold and grow. It might be that the area needs to have rock or rip rap placed around it to hold the soil in place, or the surface runoff needs to be redirected to prevent it washing out. If this is a large culvert or a large volume of water, I would strongly suggest you consult on site with a landscape architect, engineer or other professional with training and experience in correcting drainage problems. Otherwise, your local county extension or soil conservation service might have suggestions. They would probably appreciate photos and rough dimensions of the area in question. I hope this helps you get started in solving the problem.
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