Updated: Oct 23, 2021
Fortnight lilies are another workhorse in commercial landscapes, tolerating a ho-lotta maintenance and design travesties yet still they thrive. Their flowers are showy and bright, and the plant form lends itself to diverse garden themes, from Japanese-inspired to tropical environs and even container gardening. Native to eastern Africa, like our other tried and true Agapanthus, D. iridioides can help any beginning gardener build their confidence. But let's examine the don'ts in caring for and designing with this plant (including a few dos).
Give it a flat top. If you read my post about Juncus patens, then this will be a familiar story. When gardeners cut all the plants back to an even 12" or so from the ground, every cut blade will turn brown at the tip and look unsightly for a long time. Only when new leaves emerge and take their place (which is a slow process), will we forget about the military regulated haircut. I am not even sure why this is done except to chainsaw through spent flowers, which has nothing to do with the evergreen foliage. Should the plant become too unsightly or the gardener wishes to take their frustrations out on this plant, there is the option to cut it close to the ground after all danger of frost is over. I'm not thrilled about this option, but some may desire a fresh start (pssst...the best option is to divide the plant).
Cut the flower stalks before their time. This is true for many species within the iris family. The flowers bloom in succession from the same stem for as much as one year (Brenzel, ed. 2012). When one bloom is finished, another might be hidden within the stem, ready to emerge after the first. All too often, gardeners cut the stems off before they are finished, or worse, see the first "don't" noted above. Not until the stem is withering should it be removed, in the meantime:
Cut off the seed pods. Sure, the first flower blooms, dies, then a seed pod emerges that some people might find unattractive. The weight of the pod will cause stems to sag, which might also be undesirable. With this in mind, remember that more blooms can emerge, but these flowers would be lost if the seed pods are cut off along with the stems. Instead, pull the seed pods straight from the stem, as this will preserve the stem and any future blooms.
Specify plants where there is insufficient space. Generally, Dietes are rhizomatous, meaning the clump will continue to spread outward. I hesitate to note their mature spread, because over time they will continue, slowly, to expand. Just today I saw D. bicolor, another attractive species, planted in a small tree well, competing with like plants, a tree, and the surrounding concrete. In a short amount of time, they will become too large and start to decline. By this time, shoveling their removal risks damaging the tree because of its close proximity to the trunk and roots. Fortnight lilies are better served in places where they can continue to grow without interruption until the gardener is ready to divide them...the proper way to reduce their size.
D. bicolor is another option (shown above), with pastel yellow flowers, but just yesterday I saw what I believe was D. grandiflora 'Variegata' on the Stanford campus. Instead of deep green leaves like our subject plant, these leaves are striped green and white. D. iridioides 'John's Runner' is a dwarf and may be more suitable for smaller spaces, another solution to some of the don'ts noted above. There are a few other hybrids as well, to round out some options.
West Valley College Campus Location: Dietes iridioides
Cilker (west facing)
Long: 122° 0'41.65"W
Botanical Name: Dietes iridioides
Dietes: Greek, dis for two and etes for relation, implying a close relationship to two other genera, Iris and Moraea.
Fortnight: Every two weeks, as in the timing of prolific bloom
Common Name: Fortnight lily; African iris; indawo-yehlathi; isiqiki-sikatokoloshe; isishuphe somfula; wild iris; wood iris
Family Name: Iridaceae
Origin: East Africa
Positioning: Forest edge, stream edge, planters, middle ground
Garden Themes: Asian-inspired, sub-tropical/tropical, rock, evergreen, woodland, modern, rain
Uses: Border, container, mass, accent, green stormwater infrastructure (elevated slope and uplands only)
Type: Evergreen perennial
Form: Clumping, upright, spiky, grassy-appearance
Size: 3' tall and spreading
Outstanding Feature(s): Flowers
Color: Dark green
Surface: Smooth, glossy
Flower: Spring to autumn (may continue into winter). Showy, large, iris form on multi-branch stems that can rebloom after the first burst. White to 3" with hints of lavender toward the center, yellow blotches on white background, and a few brown streaks into the center.
Fruit: Year-round. Green capsule, segmented turning brown before segments open to disperse seeds. May easily germinate under the right moisture conditions.
cultural requirements, tolerances & problems
Sunset Zones: 8, 9, 12-24; H1, H2
USDA Zones: 9-11
Light: Full sun to partial shade (blooms more in sun)
WUCOLS SF Bay Area Hydro Zone: Low
Texture: Rocky, loam (native soil is decomposed granite)
Moisture Retention: Well-drained
pH: Highly acidic to highly alkaline
Branch Strength: N/A
Insects: Scale, nematodes
Disease: Crown rot, root rot, rust
Some African cultures believe that, if you have been to a funeral or entered a house with a corpse, you must chew the rhizome and spit on the ground to take the bad luck away. And if you do not chew the rhizome, an immediate member of your family is going to die.
~ Referenced by South African National Biodiversity Institute
citations & attributions
Plant Finder. "Dietes iridioides." Missouri Botanical Garden, St. Louis. Accessed on July 28, 2021, from http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=281112.
Norris Brenzel, K. (Ed.). (2012). The New Sunset Western Garden Book. New York: Time Home Entertainment, Inc.
PlantZAfrica. "Dietes iridioides (L.) Sweet ex Klatt." South African National Biodiversity Institute, Brummeria. Accessed on July 28, 2021, from http://pza.sanbi.org/dietes-iridioides.
Water Use Classification of Landscape Species. "WUCOLS IV Plant List." University of California, Division of Agriculture and Natural Resources, Davis. Accessed on July 27, 2021.
All photos by TELCS.