How to Grow Fortnight Lily — Dietes

Sharing is caring!

Dietes–commonly called fortnight lily or African iris–is a rhizomatous perennial cultivated for colorful iris-like flowers. All varieties grow quickly and produce flowers at two-week intervals throughout spring, summer, and fall.

Dietes is an iris-like plant with fans of stiff narrow, evergreen leaves growing from dense long-lasting clumps. The flowers resemble small Japanese irises; each flower consists of three outer and three inner segments. Flowers can be white, cream, or yellow often with a contrasting blotch at the base of the outer segments.

Dietes can grow in a wide range of soils as long as the soil is well-drained. Established plants can tolerate neglect and infrequent watering once established. Flower production will slow in hot, dry weather.

Dietes are a good choice for accent in gardens, around pools, along walkways, and in containers.

Dietes is a genus of six species native to tropical southern and eastern Africa.

Get to know Dietes

  • Plant type: Rhizomatous perennial
  • Growing zones and range: Zones 8-10
  • Hardiness: Hardy to Zone 8
  • Height and width: 24 to 36 inches (60-90cm) tall and often as wide
  • Foliage: Erect, linear to sword-shaped leathery basal leaves
  • Flowers: Iris-like flowers consist of three outer and three inner segments; blooms occur at 2-week intervals; each blossom lasts one day
  • Flower colors: white, cream, yellow; outer segments feature a small blotch of contrasting orange, yellow, or brown
  • Bloom time: Spring, summer, fall
  • Uses: Border, cut flowers, greenhouse
  • Common name: Fortnight lily, African iris
  • Botanical name: Dietes
  • Family name: Iridaceae
  • Origin: Tropical central and southern Africa
African Iris, Dietes iridioides
African Iris, Dietes iridioides

Where to plant Dietes

  • Plant Dietes in full sun or partial shade.
  • Grow Dietes in moist but well-drained soil.

When to plant Dietes

  • Set container-grown Dietes outdoors in spring or autumn.

Planting and spacing Dietes

  • Space Dietes 24 to 36 inches (60-90cm) apart.

How to water and feed Dietes

  • Keep the soil evenly moist but not wet during the growing period; reduce water after flowering.
  • Fertilize Dietes with a balanced liquid fertilizer

Dietes care

  • Cut back the flowering stems of Dietes iridioides after flowering.

Dietes pests and diseases

  • Rust and crown and root rot commonly afflict Dietes.

Dietes propagation

  • Sow seed in autumn or spring.
  • Divide rhizomes after flowering; divisions may be difficult to establish.

Dietes varieties to grow

  • Dietes bicolor. Rhizomatous perennial with narrowly sword-shaped, pale green basal leaves; bears pale to deep yellow flowers; 3 larger tepals ave a brown mark at the base; grows to 36 inches tall.
  • D. grandiflora, wild iris. Rhizomatous perennial with sword-shaped dark green leaves to 28 inches long; bears white flowers to 4 inches across with a yellow mark at the base of the 3 large tepals and a brown mark at the base of the 3 smaller tepals; grows to 3 feet or taller.
  • D. iridioides, syn. D. vegeta. Rhizomatous perennial with a fan of sword-shaped, dark green, basal leaves to 24 inches long; white flowers to 2 inches across with a yellow mark at the center of each.

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. has more than 10 million visitors each year.

How To Grow Tips

How To Grow Tomatoes

How To Grow Peppers

How To Grow Broccoli

How To Grow Carrots

How To Grow Beans

How To Grow Corn

How To Grow Peas

How To Grow Lettuce

How To Grow Cucumbers

How To Grow Zucchini and Summer Squash

How To Grow Onions

How To Grow Potatoes

How to Grow Olea – Olives

How to Grow Euryops