You need a heated greenhouse or conservatory where the temperature never drops below 20°C/70°F to safely grow these rare bulbous plants known in Latin as Hymenocallis. Very closely related to Amaryllis (note the similar strap like leaves) these are amongst the most beautiful of flowers carrying a heavy vanilla perfume to add to their pristine glory.
Hymenocallis come from the New World and are found from Peru to Mexico and the West Indies. They are very similar to and were once included with the Crinums though those are from Africa and Asia and are a tad hardier (and Crinums never have the daffodil like cup at the centre of each bloom).
These beautiful blooms come in clusters of up to a dozen with new ones replacing the older as these fade. You can cut these with their long stems for flower arrangements though they last longer left on the bulb. However if you have several bulbs it is worth cutting a stem or two as these are spectacular amongst other less showy specimens and make a humble bunch of otherwise mediocre flowers into a brilliant display.
Hymenocallis are definitely tender! If you are fortunate to find some of their bulbs (these are sold in the UK when stocks come available, grab them when you see them) do make sure they never get cold. Otherwise these are not at all difficult.
Like so many tender bulbs they need a free draining peat or leaf mould rich loamy compost and rain water, this preferably warm. They also like a little light feeding during their growing season. In winter some species may die down but most usually persist in leaf in which case be especially vigilant not to over-water. Be careful never to damage their roots when re-potting, nor let these dry out. At the same time you may carefully detach offset bulbs to grow up to flowering size, these plants are seldom ever grown from seed.
The connoisseur can build up a collection. The star is probably the hybrid H. Festalis (shown) which has large ornate cups frilly at the edges dripping long ‘petals’ in purest white and an exquisite scent, very similar is the other Peruvian Daffodil, H. narcissiflora. The Spider lilies, H. caribaea, H. speciosa & H. harrisiana are widely cultivated in the West Indies and even as far north as Florida, they’re much the same with smaller cups and very long narrow ‘petals’ often with a greenish hue to part and that same sweet vanilla perfume. H. macrostephana is from Bolivia and is perhaps the hardiest taking temperatures as low as 10°C/50°F. H. littoralis / americana has the added bonus of having a variegated form with creamy greenish white stripes along the leaves.