I put in an endless summer about a month ago. I didn't use manure, I just mixed in mulch with my soil. I was afraid to amend the soil too much and then when the roots start spreading past where the soil was amended it'd be in shock from the poor soil lol. So I dug the hole size the size of the pot, mixed in some mulch in the bottom and around it. Then for about 2 weeks I watered it with a 2 gallon watering container everyday unless it rained since my soil doesn't hold water that well. I also used an organic fish fertilizer right after planting when I watered it. It was a 5-1-1 which I use about weekly on all my plants outside and they are all doing splendidly.
It never got droopy or anything on me. Now I hardly water it, mainly because it has been raining about once a week and the mulch retains water fairly well. Now its starting to bloom. Yay!
ETA: I also put a 2 inch layer of wood mulch over it. It's in my semi-shade garden so the whole garden has a 2 inch layer of wood mulch which helps keep moisture longer since my soil drains really well.
Good luck with it!