Things You'll Need
Drip irrigation hoses or watering can
Water-soluble general-purpose fertilizer
Garden scissors or pruning snips
Flax lilies (Dianella tasmanica), shade-loving members of the Liliaceae family, add style and color to areas sheltered from sun. With variegated, straplike foliage and delicate, star-shaped flowers in shades of yellow and blue, flax lilies grow up to 3 feet in height with a spread of 2 feet. Hardy in U.S. Department of Agriculture plant hardiness zones 8 or 9 through 11, flax lilies are evergreen in warm climates but die back during winter elsewhere.
Apply a 2- to 3-inch layer of mulch around the base of each flax lily plant, stopping at least 1 inch from the stem. The mulch helps conserve moisture and keeps soil cool during the high heat of summer.
Water flax lilies regularly to keep the soil consistently moist. During periods of drought or for plants located in areas with direct to partial sunlight, increase the watering schedule or use drip irrigation hoses to maintain adequate moisture levels.
Apply water-soluble fertilizer, according to the manufacturer's specifications, at the start of the growing season to established flax lily plants and up to three additional applications as needed for new or struggling plants. Like many perennials, flax lilies should only be fertilized if they show sluggish growth.
Remove spent flowers and any dead or yellowing foliage as it occurs during the growing season. In colder climates, cut the entire plant back to ground level with pruning snips in late fall or early winter.
Inspect flax lilies regularly for disease or pest infestations and remove any diseased or dying foliage. Flax lilies may get mildew or leaf spots, but such diseases are uncommon when plants are sited in their ideal conditions. Scale insects can be an issue with plants grown in shady spots but are generally kept under control by beneficial predators such as parasitic wasps. Avoid overhead watering to discourage scale damage.
The University of Florida IFAS Extension recommends the use of controlled-release fertilizers with equal amounts of potassium and nitrogen and little to no phosphorous content for perennials such as flax lilies.
Established flax lilies should be divided every two to three years to maintain healthy plants.