Aha, the Cardiocrinum giganteum!
I bought one (already some years old) last year and planted it out in the shade of my hazels. In the beginning all went well, it grew quickly and had a bunch of the loveliest shiny leaves. In summer however the leaves yellowed and fell off. I was afraid the bulb would rot.
As it is such a beautiful and expensive plant I didn't want to lose it, so I replanted the bulb in a big pot and gave it a place in the cold frame. I may say it is doing well again (for the moment at least).
If my memory is still good Gertrude Jekyll wrote somewhere about preparing the soil for this kind of plants so deep that cart and horse could disappear in the pit. I thought she must have been exaggerating or at least joking. But then I took a look at a picture of hers and saw a woman probably not used to making jokes. Could it be then there was some kind of exactness in her description?
I wanted a second opinion. This is what Vita Sackville-West wrote about soil preparation for Cardiocrinum giganteum in her book "Some Flowers': "(...) any coppice say of hazel or chesnut will serve the purpose, which is to provide shade and coolness, for the Giant Lily (=CC) will stand a good deal of both. Then you must dig out a hole two or three feet deep, and fill it with the richest material you can provide in the form of leaf-mould, peat, and rotted manure. This simple recommendation reminds me of the exclamation of a friend: 'It seems to me,' she said, 'that this lily of yours has all the virtues and only (??) four disadvantages: it is very expensive to buy; the bulk (sic) takes three years before it flowers; after flowering once it dies; and you have to bury a dead horse at the bottom of a pit before it will flower at all."
A horse again!!