How to Grow Dietes — Fortnight Lily

Dietes bicolor
African Iris or Fortnight Lily, Dietes bicolor

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.

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