Here's where we started...
Today I got brave and potted and pinched the one mandevilla that had really taken off. I saved the bamboo supports that came with the plants i bought last May, and used them for supports. I looked around on the web and every site i visited told the same story - pinch the vine while they are young to encourage them to be bushier and have more than one main vine.
The plant that is in the gallon sized pot was the clipping (one of 8) that survived. It has great roots. The other pot is a layered plant that is looking better - it's definitely sending out a good, strong new shoot.
Here's a close up -
Hopefully the warmth of the window sill will inspire these ladies to put on some top growth! I'll keep you posted.
Here's what the front sunny border looked like last summer with the pink mandevilla plants climbing the walls. I hope you agree more of these plants would be an asset to that border.