- Author: Linda Lewis Griffith
- Editor: Noni Todd
By Linda Lewis Griffith UCCE Master Gardener
Planting zones: USDA Hardiness Zones 8a to 11
Size: vigorous growing clumps up to 4 ft. tall and 3 ft. wide
Bloom season: spring, summer and fall. In milder areas may bloom into winter.
Exposure: full sun to partial shade
Pruning needs: none necessary
Water needs: Established plants are drought tolerant but bloom more freely with regular watering.
This South African native is a popular choice in California gardens because of its colorful flowers and suitability to a variety of landscape situations. A member of the iris family, it produces large white flowers with violet and yellow markings and is the showiest of the fortnight lily species. Its blooms seem to come at two-week intervals, hence the common name, fortnight lily. Each bloom lasts only one day but is quickly replaced by another one. Flower cycles occur on the same stalk; breaking off forming seed pods increases flower production and minimizes the spread of unwanted volunteer plants. Flowers are followed by 2 inch long green capsules containing very dark brown seeds that are dispersed when the capsule splits open.
Dietes grandiflora grows almost anywhere when planted in rich, well-drained soil. It can survive neglect and minimal water, but foliage quality and flower production suffer when conditions become too hot and dry. It is also frost hardy, tolerating temperatures down to 25 degrees F. Fortnight lilies are popular for en masse plantings and as accent plants in gardens, around swimming pools, along walkways and in containers. They are equally at home in both lush landscapes and low-water gardens. Growth patterns may be more robust than expected, causing them to quickly outgrow containers or small planting areas.
Overgrown clumps do best when divided every 4 to 5 years after flowering in the autumn or winter. Split clumps with a fork and pull the divisions into smaller pieces with your hands. Make sure each piece has a good root system and several new shoots. Discard old, woody or dead portions of the plant. New, smaller plants may be replanted in the same area or in another location. Firm in lightly after planting and water thoroughly.