Trying to grow Ipomoea lobata

I am always tempted by climbers. They are great for filling odd spaces and experimenting with the annual varieties is great fun! Seduced by the beautiful display of Ipomoea (Mina) lobata I saw last year in St James's park, London, I ordered some seedlings from Sarah Raven and 8 lovely little plants arrived this spring - April I think!.
After a week or so I decided it should be safe to plant them out. Cautious, I only planted out 3, gave one to a friend and kept 4 inside in pots. Alas, the ones I planted out very soon succumbed to the unexpected late frosts. Looking a little sad and straggly I put my remaining 4 outside to harden off in early May. One was attacked by snails and proved insufficiently strong to recover so I brought the other 3 back indoors. They did not flourish - the leaves became distorted and pale and the plants grew straggly. Reading about them it seems they do not like rich living so I transplanted into rather poorer garden soil than the compost I initially used. I popped 2 in the greenhouse and they began to flower almost immediately with hardly any leaf/stem growth. Another I put in a window box with some petunias.
I am watching and waiting eagerly. Here is a picture of the healthiest when first transplanted. I will report progress - hoping for the best. Any advice very welcome!