I have a retaining wall, 50ft long, 4-6 ft high. Do you plant on top with vine going down, or bottom with vine going up? I have no soil at bottom but could build a box to hold soil.
Where to Plant the Purple Hyacinth Bean Vine
Certified GKH Gardening Expert
They would normally be grown on a trellis or support of some kind.
I see no reason why planting them to trail down the wall would not work.
Purple Hyacinth Bean Vine is an annual, so if it does not work this year, change it up for next year.
Here is a link.