The silver foliage and blue spiky blooms of Sea Holly (Eryngium) is from south eastern Europe and grows on hills and mountain sides with good drainage so a fast draining soil and sun are essential. Like many perennials however Sea Holly does not live forever and will grow  weak with age. Often it will reseed so a fresh young plant can replace the one that is aging out. If you dug up the plant and the soil was dry it could be suffering from lack of water. I have found that this plant will look wilted and weak during dry spells and seems to perk up quickly if given water. It also responds well to fertilizer so don't be shy about adding Osmocote around the base of your potted plant. I suspect your potted Sea Holly will do fine this summer in a pot if it is kept watered and fed but next spring look for fresh young plants at your local nursery or search the area where it was growing for seedlings. Remember to harvest those spiky blooms once they dry and enjoy all winter in arrangements. Keep growing, Marianne Binetti