It is easy to see how Strobilanthes was dubbed "Persian shield." The leaves have the appearance of little pointed armor shields ready for battle, with a flashy, purplish iridescence and a silvery metallic sheen. Although this plant's name is "Persian," it is actually native to Myanmar (formerly Burma), not Persia. In hot climates, it is an evergreen subshrub. In cooler climates, it is grown as an annual plant or herbaceous perennial, and is also popular as a houseplant because it tends to bloom during winter. However, the vibrant purple color often fades with age, and both outdoor perennials and indoor potted plants are often discarded after a few years.
As an annual, Persian shield is usually planted from potted nursery starts in spring after the soil has fully warmed. It grows relatively fast in warm, humid conditions; a small potted nursery plant will become a bushy 2-foot plant within a few weeks.
This plant can serve as an evergreen subshrub in regions without winter frost, where temps remain above 45 degrees Fahrenheit. In transitional regions (zones 8, 9), it sometimes grows as a root-hardy perennial, dying back to ground level in winter in returning in spring. In colder regions, it is a very popular garden annual and potted houseplant. But because the colorful foliage fades with time, Persian shield is more often grown as an annual in all regions.
Grown in the garden, Persian shield performs well in warm conditions in locations with dappled sunlight, if given plenty of moisture. Failure is usually traced to conditions that are too dry or too cold. Potted nursery starts should not be planted outdoors until the soil is well warmed and nighttime temps remain reliably above 50 degrees Fahrenheit.
Grown as annuals, these plants usually do not flower before winter cold sets in, and most gardeners don't worry about flowers, pinching back the plants early to encourage bushy growth and more foliage. Indoors, the plant may flower in winter, but the flowers tend to be small and are outshined by the leaves.
Light
In its native environment, Persian shield is found in dappled light conditions on the edges of tropical forest clearings, and it will do best in gardens that mimic this environment. Persian shield accepts full sun in cooler climates when grown as an annual, though partial shade is best suited for showing off the shiny foliage. The color can appear a little washed out in full sun. If kept indoors, it needs plenty of bright light—even some direct sun—to keep its color.
Soil
Persian shield grows well in the neutral range of soil pH and can tolerate slightly acidic soil. Keep the pH between 5.5 and 7.5.
Water
The less water the Persian shield plant gets, the more shade it will need. The plant will quickly droop if it doesn't receive adequate water, but it typically bounces back quickly after a drink. A full 1 inch of water per week is a minimum for garden plants, but very hot conditions may require daily watering to avoid leaf wilt.
Temperature and Humidity
Persian shield does best in warm temperatures (above 60 degrees Fahrenheit) and sultry humid air. It is fully evergreen in USDA zones 10 and 11, and can grow as a standard perennial in zones 8 and 9, where it dies back to the ground but usually returns in the spring. Elsewhere, it can be grown only as an annual, though a very good one. Even in warmer climates, this plant is often used as an annual rather than perennial.
If growing indoors, make sure it has humid conditions. Dry air will cause the leaves to dry and drop. Misting daily is recommended, but be sure to use soft water, as chlorine will damage the leaves.
Fertilizer
If grown in rich soil with plenty of moisture, Persian shield should only need light feeding at the start of the season and again about midway through the summer. For potted plants, the recommendation is to give them light feedings (half-strength) every two to four weeks.
As with most foliage plants, nitrogen is the more important nutrient. Use a fertilizer formula that is weighted toward nitrogen, such as a 12-6-6 mixture. For the amount, follow the label instructions.