From a Danish botanist:
"Cardiocrinum is a nutrient demanding plant and adding natural manure or ordinary lawn fertilizer in the spring will pay off. "
http://www.viscum.dk/eng-sider/cardiocrinum.htm
I'm no gardener but reading that lot suggests to me that you need some good old-fashioned horse manure! The good news is that it's cheap; 50p per sack up the road from me ;-)