How to Grow & Care for African Iris (Dietes iridioides)

African iris in garden, white petalled flowers with yellow and purple accents

Sundry Photography / Getty Images

The African Iris (Dietes iridioides) is an evergreen plant that grows well in warmer zones, with a long season of flowering from spring through fall. This plant originates in South Africa. It has strappy narrow blue-green leaves that remain upright throughout the season. It can be grown as a perennial in zones 8 to 11, and in colder zones is commonly grown as an annual. It is also sometimes known as Dietes grandiflora and its taxonomy classification has changed somewhat over the years.

This attractive plant has a round, six-petalled creamy white flower with a smaller four-petalled blue-purple flower that emerges in its center, with bright yellow accents running down the center of the white petals. The blooms fade rather quickly but new ones are produced continually during the blooming season.

Common Name African iris, fortnight lily
Botanical Name Dietes iridioides 
Family  Iridaceae 
Plant Type  Evergreen perennial
Mature Size  2 - 4 ft. tall
Sun Exposure  Partial to full sun
Soil Type  Moist well-drained loam
Soil pH  Slightly acidic 
Bloom Time  Spring through fall 
Flower Color  Blue, white
Hardiness Zones  8 - 11 (USDA)
Native Areas  South Africa

African Iris Care

The African iris is commonly used as a ground cover in mild climates due to its long season of bloom, vigorous growth habit, and relatively low maintenance. Planted in a suitable location, it will give many years of worry-free blooms and provide plenty for dividing and sharing. Like other irises it benefits from frequent dividing, at least every 2 or 3 years.

Six petalled white flowers with yellow and blue markings

Maureen Bates Photography / Getty Images

Light

Thought it thrives best in full sunlight, the African iris will bloom in partial sunlight. In partial sunlight blooms may not be as vigorous. Ideally, it should get six hours of sun per day in its blooming season if possible, and afternoon sun is a bit stronger than morning sun for placement of this perennial.

Soil

These plants like a rich, well-drained loamy soil. Many irises are not fussy about soil, but the African iris requires good drainage to keep the rhizomes healthy. If you have clay soil, add some compost or other amendments to improve drainage before planting African iris.

Water

Once established, the African iris is very drought tolerant and doesn't need any special watering. In times of extreme drought it might need to be watered. In its first two years, or right after planting, it should be watered regularly.

Temperature and Humidity

Because they originate in a tropical climate, the African iris is not cold tolerant and will not survive as a perennial in places with harsh winter temperatures. Being very drought tolerant, they may not do too well in area with high humidity in summer. Dividing them frequently allows air circulation to prevent any issues caused by too much dampness.

Fertilizer

The African iris can benefit from fertilizer during the growing season. Apply a basic all-purpose plant food in spring and mid-summer to help promote blooms and keep insects at bay. Apply fertilizer several inches from the plant to prevent burning the roots.

Pruning

The African Iris will tend to bloom quite heavily during the peak of the summer season. Deadheading the blooms will keep your plants looking fresh and lively. You may also trim off any brown or dead or damaged leaves. Clean your tools before cutting the leaves (a good garden habit) to avoid any bacteria that may lead to root or crown rot.

Propagating African Iris

Like other kinds of irises, the African iris has a clumping growth habit and spreads via rhizome, but it also spreads when its seed pods bend down to the ground to form new roots. The best way to propagate is from existing plants after dividing. But they can also be grown from seeds.

To divide by root division:

  1. To get the root divisions you will need to divide the plant, or obtain divisions from someone else.
  2. Divide as you would similar clumping irises such as Japanese iris: dig them up, shake off excess dirt, and use a sharp knife to cut the roots.
  3. Plant in potting medium or well-drained soil. Plant indoors in the fall, or outside after last frost date in spring. Be sure the plant will get at least six hours of direct sunlight per day; eight hours of indirect sunlight may be sufficient. Be sure to water regularly.

To propagate from seed:

  1. Gather seeds from the pods in the fall.
  2. Plant seeds indoors in the fall, or after last frost date in spring. The seeds do not need to be soaked or cold stratified.
  3. Plant in well-drained soil where there is at least six hours of direct sunlight per day. Water lightly and frequently. Seeds should begin to germinate within four weeks.

Overwintering African Iris

In growing zones that are too cold for it to survive the winter, this plant can be grown successfully as an annual. It can be dug up and overwintered and replanted in spring, much like digging up other perennials such as cannas or dahlias that are not cold tolerant. If you plan to dig up your African iris in winter, shake off any extra soil, and allow the rhizomes to dry thoroughly before storing them in peat moss or sand in a cool dry place. They can be replanted in spring when temperatures have warmed up and and danger of frost has passed.

Common Pests and Plant Diseases

Though it is generally low maintenance, there are a few occasional diseases and pests affecting the African iris. The most common involve crown rot or root rot. This tends to occur when the plant remains damp for too long. Prevention is the best way to address this: plant in well-draining soil, divide the plant frequently to keep the roots healthy, and plant in a location with good air circulation. If your plant does develop rot, dig it up, cut off the affected area, and replant. Autumn is a good time to divide and replant them to keep them healthy.

There is also a possibility of fungal and bacterial diseases, including rust, Botrytis blight, and fungal leaf spot. Fungal diseases can be recognized by the appearance of yellow or brown spots on the leaves; left untreated these diseases can spread to the entire plant. In wet, warm weather, bacterial leaf spot may occur; this causes small spongy, wet spots to appear along the leaf margins, and can cause bigger watery lesions to spread. If your African iris shows signs of fungal or bacterial disease, remove all damaged plant parts and allow the plant to dry out well, and avoid overwatering.

Common pests that may affect your African iris include aphids, iris borers, and nematodes. Iris borers attack the plant in their larval stage and can quickly cause widespread damage. This can be prevented with the weekly application of neem oil spray. This will also help prevent aphids. Nematodes (Ditylenchus destructor) may attack the young roots of the plant and cause browning of leaves and wilting of roots. To prevent this, remove any damaged or diseased plant parts and practice good hygiene with clean tools to prevent infection or spread.

How to Get African Iris to Bloom

Once an African iris is two years old, it will tend to bloom year round. When it is younger, it should bloom consistently throughout the spring and summer. The flowers are somewhat short-lived but there are usually plenty more waiting to bloom as the flowers fade and drop off. If your African iris isn't blooming consistently, make sure it's getting enough sun. It needs at least five hours of direct sunlight per day. You might also try watering it a bit more often and see if keeping the soil slightly moist helps the plant to form more flower buds. Finally, regular fertilization will also help your plant form more blossoms.

FAQ
  • Can you grow African iris as a perennial?

    The African iris is only cold hardy to zone 8, so it will not survive in a location where the ground freezes.

  • Can you grow African iris in containers?

    If you are growing this plant as an annual and overwintering it, it should do fine in a container for the growing season. If growing as a perennial, the African iris tends to spread rather freely and growing it in a container may cause overcrowding which can lead to root rot, so it is best to plant in the ground.