Answer: It sounds as though you're doing all the right things. I wonder, though, if the soil isn't heating up enough in the spring to wake the plant up and get it off to a good start? You might try covering the bare soil with black plastic to absorb the heat. If that's a little over the edge in terms of garden design, how about laying bricks or flagstone over the bed? Anything that will absorb and then reflect heat will warm the soil up earlier in the season and make your passionflower want to grow.
Hope this works!
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