Whether you grow shamrock plants indoors as a houseplant or outdoors in frost-free zones, oxalis triangularis is simple to grow and care for if you use correct proportions of water and sunlight. Purple shamrocks have great visual appeal, sporting bright purple, triangular leaves accented by pink or lavender blossoms. Despite the Celtic overtones of its common name, the plant is native to Brazil.
To grow shamrocks, place up to five bulbs in an 8” pot to create a houseplant, or tamp the bulbs into the soil outdoors, spaced 3” apart and 1 to 2” inches deep. Water the soil well, but make sure it drains adequately, as too much moisture can cause the roots to rot. You can expect to see flowers within 10 weeks.
The purple shamrock is sensitive to light, and its leaves close up at night and in overcast conditions. Plant or place it an environment free from temperature extremes. The brighter the light source, the more colorful the foliage and flowers. Avoid prolonged periods of direct sun and heat, however, which can cause the shamrock to go dormant prematurely.
In general, aim for a daytime temperature of 60-70F, especially when the plant is blooming. When planted outdoors, purple shamrocks should fare well in frost-free regions that correspond with the U.S. Department of Agriculture’s “hardiness” zones 6 through 10.
In general, when watering your shamrock, keep the soil barely moist, and allow the top inch of soil to dry before the next watering. Use a houseplant fertilizer mixture every two to four weeks to maintain the plant’s overall health.
Like other plants grown from bulbs, the purple shamrock requires one or more “rest periods,” particularly during autumn. If your plant looks “tired” after it blossoms, stop watering it and let it go dormant for approximately one month, then fertilize and water as usual once it rejuvenates.