The Fortnight Lily ( Dietes iridioides or Dietes bicolor) is a beloved evergreen perennial, prized for its delicate, iris-like flowers and easy-going nature. Native to East and Southern Africa, this plant has become a popular choice for gardens in warmer climates, particularly in Southern California, where it is well-adapted. Its clumping habit and long bloom season make it a valuable addition to various landscape styles, from sustainable gardens to coastal plantings.
Understanding the Fortnight Lily
The Dietes genus comprises five species, with four originating from Africa and one from Lord Howe Island, east of Australia. Dietes iridioides (also known as Moraea iridioides) is a vigorous evergreen that forms clumps of long, upright, narrow, dark green leaves. Dietes bicolor, also known as the African Iris or Butterfly Iris, features pale yellow flowers with rich maroon spots.
The plant's common name, Fortnight Lily, comes from its unique blooming pattern. It produces flushes of flowers at approximately two-week intervals from spring to fall, and sometimes well into winter in milder climates. Each flower, which resembles a small Japanese Iris, lasts only a day, but the plant continuously produces new ones.
Identifying Key Characteristics
- Foliage: The Fortnight Lily features upright, sword-like foliage and strappy leaves that create a tidy, fan-shaped clump, providing year-round garden interest. Leaves are long, upright and narrow, reaching 2 to 4 feet tall.
- Flowers: The flowers are iris-like, with three outer and three inner segments. Dietes iridioides produces small white flowers with gold markings on the outer petals and violet on the inner petals. Dietes bicolor has soft, buttery yellow flowers with three chocolate-maroon blotches near the base.
- Growth Habit: It is a rhizomatous evergreen perennial, meaning it spreads via rhizomes (underground stems) to form clumps.
- Hardiness: Typically hardy in USDA zones 9-11, but can tolerate occasional hard frosts, especially in Zone 8 and up. In colder regions, it may benefit from protection.
Optimal Growing Conditions
Fortnight Lilies are adaptable plants, but providing the right conditions will encourage healthy growth and abundant blooms.
- Sunlight: While they tolerate some shade, Fortnight Lilies bloom best in full sun. However, in hotter climates, light afternoon shade can be beneficial.
- Soil: They thrive in moderately fertile, moist, well-drained soils. They can tolerate poor soil and infrequent watering once established.
- Watering: Regular watering is ideal, especially during the blooming season. However, once established, Fortnight Lilies are drought-tolerant.
- Climate: These plants are well-suited for Mediterranean and coastal gardens.
Planting and Initial Care
- Choosing a Location: Select a site that receives full sun to partial shade and has well-draining soil.
- Soil Preparation: Amend the soil with compost to improve drainage and fertility.
- Planting: Dig a hole that is as deep as the root ball and twice as wide. Place the plant in the hole and backfill with soil. Water thoroughly after planting.
- Watering: Keep the soil consistently moist, but not waterlogged, until the plant is established.
- Fertilizing: Apply a balanced fertilizer in spring to promote growth and flowering.
Ongoing Care and Maintenance
- Watering: Established Fortnight Lilies are drought-tolerant, but they benefit from regular watering during dry periods.
- Fertilizing: Fertilize in the spring with a balanced fertilizer to encourage blooming.
- Deadheading: While not strictly necessary, deadheading (removing spent flowers) can improve the plant's appearance and encourage more blooms.
- Pruning: Clip off any leaves that die to keep the plant looking tidy.
- Division: Divide clumps every 3-5 years to rejuvenate the plant and prevent overcrowding.
Managing Overgrown Clumps
After several years, Fortnight Lily clumps can become very thick and congested, with fresh new leaves mixed in with old, spent foliage. Cleaning up a large, old clump can be challenging. Here are a couple of solutions:
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Option 1: Cutting Back Foliage
- In the fall, cut off all the foliage as close to ground level as possible, removing both the good and bad leaves. This can be done with sharp electric hedge shears or hand-held hedge shears.
- After cutting back the foliage, fertilize and water the plant to encourage new growth.
- Allow the foliage to re-sprout from the ground.
Option 2: Digging Up and Dividing
This is often the best option for rejuvenating overgrown clumps.
- The best time to do this is in the fall or winter.
- Water the clump thoroughly a day or two before dividing to make it easier to dig up.
- Use a garden fork to dig the clump out of the ground. The roots are not deep, so this should not be too difficult.
- Once the clump is out, use a sharp spade or knife to cut it into sections.
- Discard the old, messy center of the clump and keep the healthy divisions.
- Use clippers to clean up each division, removing spent foliage and old, woody rhizomes. Retain the fresh, new growth.
- Amend the soil by digging in a 4-inch layer of fresh compost.
- Mix a balanced organic fertilizer into the top 6 inches of amended soil, following the package directions for new plantings.
- Water the bed and let the soil settle overnight.
- Replant the new divisions back into the ground.
Propagation
Fortnight Lilies can be propagated by division. This is best done in the fall or winter when the plant is not actively growing.
- Dig up the clump and divide it into sections, as described above.
- Replant the divisions in a new location or back into the original location after amending the soil.
Potential Problems and Solutions
- Pests: Nematodes can be a problem.
- Solution: Use appropriate nematicides or employ cultural practices to minimize nematode populations.
- Overcrowding: Clumps can become overcrowded after several years.
- Solution: Divide the clumps every 3-5 years.
- Self-Seeding: Fortnight Lilies can self-seed readily, potentially becoming a nuisance.
- Solution: Clip off the green seed capsules after bloom to prevent self-seeding. However, leave the stems of the white variety on the plant as long as they continue bearing flowers for several years.
- Unsightly Foliage: Old, spent leaves can detract from the plant's appearance.
- Solution: Regularly remove dead or dying foliage. Cut back the entire plant in the fall if necessary.
Landscaping Uses and Design Tips
Fortnight Lilies are versatile plants that can be used in a variety of landscaping applications.
- Borders and Edges: Plant along borders and edges to create a neat and tidy appearance.
- Groundcover: Use as a groundcover in areas with well-drained soil.
- Rock Gardens: Incorporate into rock gardens for a touch of elegance.
- Containers: Grow in containers on patios or balconies.
- Sustainable Gardens: Ideal for sustainable gardens due to their drought tolerance and low maintenance requirements.
- Coastal Gardens: Tolerates coastal conditions, including salty spray.
- Pollinator Gardens: Attracts bees and other pollinators.
- Fire-Wise Landscaping: A great fire-resistant landscaping plant.
- Moon Gardens: The flowers seem to glow during twilight hours, making them perfect for a Moon Garden.
Varieties
- Dietes iridioides (also known as Moraea iridioides): Features white flowers with gold and violet markings.
- Dietes bicolor: Displays pale yellow flowers with maroon spots.
- Dietes grandiflora (Dietes vegeta): A vigorous evergreen with white flowers.
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