Acidanthera plants are native to western Abyssinia, but they grow well as houseplants in the UK. The flowers resemble the gladiolus, but are more orchid-like and dainty with black-purple centres surrounded by six white petals. The stems of the acidanthera can grow up to 1.2 metres (4 feet tall) and will have up to eight buds. Container acidanthera plants can be started in March so that the plant has flowers during the late spring and throughout the summer. If given properly prepared growing medium, acidanthera does not need fertiliser.
Prepare the medium for the acidanthera. Use one part peat moss, one part perlite and one part garden soil. Add a dusting of lime and mix the ingredients together. Add the medium to a 15 cm (6 inch) container with drainage holes in the bottom. Plant the bulb twice as deep as its size in the medium. If the bulb is 5 cm (2 inches) long, plant the bulb 10 cm (4 inches) underground.
Water the plant to keep the soil moist, but not wet and soggy. Stick your finger in the soil 2.5 cm (1 inch) deep. If the soil is dry, add water. If the soil is wet, not damp, do not water.
Place the container in a window where it will receive full sunlight. Southern and western windows will give the acidanthera more than four hours of direct sunlight, which the plant needs to grow and bloom.
Keep room temperatures between 10 and 24 degrees C (50F to 75F), with medium humidity. Add more humidity in rooms with little humidity by placing a jar of water next to the acidanthera in direct sunlight. During the summer months, plants can be moved outdoors to patios to continue growing and blooming. Plants must be brought indoors before the first frost.
Stop watering the plant when the foliage and flowers die back. Cut the foliage down to the medium. Do not water the acidanthera for three to four months to give the bulbs a rest period. Move the container away from the sunny window, but keep the heat in the room the same.
Remove the bulbs from the spent medium in March. Mix another batch of soil and plant the bulbs in the same way. Start watering the plant again and place it in a sunny window.