Alum lilies

[Old Daffodil]

Does anyone have any advice on growing Alum lilies in pots? My lilies are growing at a rate of knots at the moment and I wondered if it needs some food of some sort. I bought them here in Turkey a couple of years ago and have not done anything to them except put them out in the rain sometimes and keep them sheltered near to the house. Surely the soil will need some sort of nutrient added for them to keep growing as they are?
Any advice appreciated.  

[Firo]

Mine are in the garden in Uzumlu and every year they flower. Nothing added apart from general garden fertilizer along with the rest of the garden.

[ovaciksarah]

Put mine in the pond last year and they never stop flowering

[Elsa Padfield]

Mine didn't like pots and thrive in the garden where they need no looking after - apart from deadheading etc