Evergreen, lance-like leaves grow from the swollen bulb-like bases on clivia lilies (Clivia spp.). Four different species exist, but most commonly grown in gardens is Clivia miniata, or hybrids of any of the species. These perennials are native to the dry, shady woodlands of South Africa. They may be grown in containers indoors or outdoors where winters are cool but frost-free: U.S. Department of Agriculture (USDA) hardiness zones 10 and warmer.
A key consideration that must be made when successfully growing clivias in the ground or in containers is the need for a coarse potting medium. The roots of the bulbs need to be moist, but the water must freely drain away and allow penetration of air to prevent rot. Mimic the natural growing conditions that clivia plants endure in their native habitat: a mixture of some soil particles with lots of coarse and fine bits of organic matter like bark and compost, as well as some bits of sand and gravel.
Grow clivias out of direct sunlight. There are a couple ways to provide the ideal partially shaded light exposure. Indoors as a houseplant, position the container just out of the reach of direct sun rays through windows, but exposed to the very bright indirect light. Outdoors, clivia lilies can be planted under the branches of tropical evergreen trees that allow dappled, shifting rays of sun to dot the foliage. Or, shade cloth netting can be placed over an arbor with plants under it to diminish the intensity of the sunlight, but still be bright enough to allow for the reading of a book, for example.
During the warmth of the growing season, from mid-spring to early autumn, water the soil freely to keep it consistently moist. Do not over-water by creating a soil that is soggy to the touch. Supplement natural rainfall as needed to keep the soil moist but never overly wet. In the cooler months from mid-autumn through winter, greatly reduce watering so that the soil remains slightly dry. Err on the side of under-watering this time of year.
Seasonal Temperature Needs
Clivia plants tolerate low temperatures down to about 36 degrees F, according to Roger Mercer and Sir Peter Smithers of the International Bulb Society. In winter, the plants need a cool, dry "resting period" where temps drop to 45 to 50 degrees, with daytime highs between 60 and 65 degrees (a warming of about 15 degrees over the day). By summertime, the added warmth and watering allows the plants to tolerate temperatures well into the 80 to 90 degree range as long as direct sun rays do not reach the plants. Spring and fall are intermediate periods, the gradual transition to the cool, dry winter and the hot, more rainy summer climates that these plants are naturally accustomed.
Fertilize the clivias freely (one per week) as part of the increased watering regimen in growing season until the flower stalks are formed and visible. Use a liquid fertilizer that is high in phosphorus (like 10-20-10) to encourage flower production, as too much nitrogen simply encourages leafy growth. Christo Lötter of the Clivia Society recommends that you ensure your fertilizer contains potassium so that the plant tissues are strong and flowering occurs on longer stems, rather than being stunted and hidden among the strappy leaves.
In general, clivia bulbs and roots resent disturbance. Consider digging and transplanting bulbs only after the flowering season ends, but if at all possible, in either spring or summer since the bulbs and roots establish better with ample time left in the growing season, according to Bing Wiese of the Clivia Society. Be gentle with the roots; wet them with a garden hose to gently pry apart bulbs and roots without having to cut or break them.