Answer: You don't mention that it has to be a flowering vine so how about a variety of hedera (ivy). Some great varieties are Hedera helix 'Goldheart', Hedera helix 'Buttercup'. Another good ivy is Parthenocissus triscupidata 'Robusta' (Boston Ivy - Ampelopsis veitchii). This one does have a bloom and probably carries the best chance of survival in the shallow soil. The slag layer is going to be a challenge for anything you try to plant there. You may want to consider building a raised bed or placing a few half whiskey barrels at the base of the trellis and plant the vines in those and then train them up the trellis. If you are looking for a flowering vine for shade, perhaps you could try Lonicera japonica 'Halliana' (Hall's Honeysuckle) or Akebia quinata (Fiveleaf Akebia Vine).
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