You might try and grow Acidanthera without a greenhouse, but only when growing in one will they come into their full glory. These are very tall, rather elegant plants when in grown in tubs under cover.
Outdoors however, they become stunted, beaten and can suffer badly from strong winds. More importantly, they also dislike cold and wet weather and die if ever frosted.
This however, is not at all surprising since these are members of the Iris family and come from the mountain slopes of Abyssinia in East Africa.
There are but a few species of which only one, Acidanthera bicolor variety murielae is found in general cultivation, but this is widely available just because it is so good.
In leaf at the start of the year, this much resembles one of its near relatives the gladioli, and indeed it is now sometimes called Gladiolus callianthus c.v. mrielae, however, Acidanthera leaves carry on growing and are much taller and far slimmer.
The orchid like, pristine white blooms have a maroon blotch and are most decorative,they also have a delicious scent that is capable of perfuming the whole greenhouse. These flowers come in sequence along a slender, slightly curling spire, whereas most gladioli have been bred to blow all the flowers on any spike, all at the same time.
Acidanthera can be used as cut flowers, though to keep their display neat, you need to remove faded blooms, as new ones open with a half dozen or so in total.
A large tub of any respectable potting compost kept just moist (but never water-logged), will suit them. The corms are planted in spring, a hand’s breadth deep or so, and about the same or more apart. They need a light position and careful watering, light feeding and good ventilation, but on a whole, they are not at all difficult to keep.
It is wise to deadhead them to stop energy being wasted on seeds, as they sometimes form pods. But there really is little to do until late autumn when the leaves brown and wither and eventually break away. Ideally, once the corms are dried off they are extricated, the biggest ones saved in a cool frost free, dry place for replanting and all the small cormlets planted up in trays to grow on.
However, if you just dry them off in the tubs, leaving the big and small corms in the dried compost, they will store more safely under the bench or anywhere that is frost free. Left unthinned over the years, they become congested and eventually, you will have all leaves and few flowers.
Still, you can let them go for a few years and then sort them out in spring and start again with the best.