Named for the pale glow of their flowers, moon lilies (Datura wrightii) stand out among other native wildflowers. They come from the southwestern United States and northern Mexico, and work well as a low-maintenance native landscaping plants. The delicate beauty of their flowers belies the plant's extreme toxicity, which can make it a liability in yards where children and pets play.
Moon lilies look similar to other members of the Datura genus, including their white, trumpet-shaped flowers and large, dull green leaves. At 2 to 3 feet tall and 6 to 8 feet wide, their low and sprawling shape sets them apart from shrubbier species and makes them unsuitable for smaller gardens. Their flowers emerge from midspring until fall, opening at dusk and lasting until noon the following day. Once the flowers fade, they are replaced by round, spiny fruits that lend the plant another common name: thorn apple. One unfortunate physical characteristic of the moon lily is its highly unpleasant smell, which is emitted whenever the leaves, stems or flowers are disturbed.
True to their desert origins, moon lilies are heat-loving and drought-tolerant plants. They perform best in U.S. Department of Agriculture plant hardiness zones 9 through 11, but will grow elsewhere as annuals or as potted perennials if moved to a warm spot during cold weather. A southerly exposure with bright sun and ample warmth is best, although they may benefit from light midday shade in hotter areas to keep their leaves healthy and hydrated. They are not fussy about soil type as long as it drains well, and they will tolerate alkaline or calcareous soils with minimal damage.
Moon lilies require minimal upkeep or maintenance if they are grown in a suitably warm, sunny site with fast-draining soil. They may become weedy or unwieldy with age and will benefit from occasional care to improve their appearance. Deep, biweekly watering during the summer will encourage lush growth and abundant flower production, although you should not water them in winter because natural rain is enough. Pruning, while not absolutely necessary, will help keep the plant's size in check if done during the late autumn or winter dormant season. Fertilizer is not recommended for these plants, but you can side dress them with compost or mulch to keep their roots healthy and discourage weed growth.
Their beauty and minimal care requirements make moon lilies a desirable addition to native plant and water-wise landscaping, particularly in warmer climates. Sunny perennial beds and borders benefit from their striking, 8-inch-long flowers, although their immense size and unwieldy growth habit allow them to easily overtake less assertive plants if they are grown under cramped conditions. You can grow moon lilies in containers, particularly in colder climates where they die back each year. This makes it easier to move the plants to a warm overwintering spot while helping keep their growth in check. Always use pots with drainage holes for moon lilies.
Before planting moon lilies, it is vital to understand their drawbacks. All parts of the plant contain highly toxic alkaloids, including scopolamine, atropine and hyoscyamine. Inhaling the flowers or ingesting minute quantities of the plant can induce serious symptoms, such as paralysis and an increased heart rate, which can lead to premature death. Survivors of moon lily poisoning may also suffer from permanent organ damage and mental impairment. For that reason, moon lilies may not be a suitable choice of ornamental plant where children and pets play. Anther potential drawback of moon lilies is their propensity to self-seed. Deadheading the plant after flowering will prevent seed production, and it may also encourage a longer, more prolific blooming period.