Several plants bear the four-leaf clover of Irish lore, including the lucky clover (Oxalis tetraphylla) and false shamrock (Oxalis acetosella). Most produce compound leaves with three leaflets, although occasionally a four-leaf stem will emerge. A properly cared for four-leaf clover plant will delight you years with its delicate foliage and dainty flowers. But no amount of care will guarantee you get a four-leaf clover -- that takes luck, pure and simple.
All four-leaf clover plants need water to survive, but the amount varies with the season. Keep the soil evenly moist, but allow the surface to dry out between waterings to prevent root problems. Water potted plants until a little bit drips from the drainage holes at the base. Water outdoor four-leaf clover plants weekly during the summer, moistening the soil in the top 6 inches. Dormant, nonblooming plants need little to no water, especially if they are a tuberous variety such as lucky clover. Keep the soil on the dry side, watering only if the foliage is wilting slightly.
Even during their active growth phase, four-leaf clover plants need little fertilizer. A light monthly application of balanced 15-15-15 fertilizer will do, although varieties with showier flowers, such as lucky clover, also benefit from a blooming fertilizer with an N-P-K analysis of 7-9-5. Combine 1/4 teaspoon of fertilizer with 1 gallon of water and replace one watering per month with the solution. Reduce feeding to every other month after blooming and don't fertilize during the dormant period and in the winter when the plant's growth slows.
Pruning and Grooming
Established four-leaf clover plants rarely need pruning, although they may need some light grooming to remove leggy stems or spent flowers. Full-sized pruning shears are too large and unwieldy to work on four-leaf clover plants, so use a pair of small nail scissors to avoid accidentally damaging the slender, tightly packed stems. Snip off the unwanted stems and flower stalks at the base and discard them. Before pruning, soak the scissor blades in full-strength household disinfectant or a mix of equal parts rubbing alcohol and water for five minutes to sanitize them, then rinse them and allow them to dry.
Four-leaf clover plants often decline with age, producing fewer flowers and sparse foliage. One common cause is a lack of dormancy. Dormancy should last for several months after blooming while the plant rebuilds its energy stores. Reducing water, fertilizer and light intensity will allow the plant to rest, effectively allow it to "reboot." Move a potted four-leaf clover plant to a cool, dim spot, such as a room with north-facing windows, for three to four months. Don't fertilize and water only enough to keep the plant from wilting. Tuberous species, such as lucky clover, need no water during dormancy; they will survive off the moisture stored in their rhizomes. Stop fertilizing and watering garden-grown plants for a few months after blooming.
Four-leaf clover plants rarely suffer from pest infestations, but they may attract whiteflies, mealybugs or aphids if grown near other infested plants. Small numbers need no treatment, but more advanced or bothersome infestations can be treated with nontoxic insecticidal soap. Mix 2 teaspoons of insecticidal soap in 1 pint of water. Spritz the solution onto the plant, paying special attention to areas where the insects congregate. Rinse off the soap after two hours to prevent foliage damage, then reapply it every four to seven days until the insects are gone.
The hardiness of four-leaf clover species varies. Lucky clover grows best in U.S. Department of Agriculture plant hardiness zones 8a through 10b, while false shamrock grows in USDA plant hardiness zones 6a to 9a. In colder climates, they must be grown in pots and overwintered indoors. When overwintering indoors, place the plant in a room with south-facing windows where temperatures stay above 40 degrees Fahrenheit at night. Keep their soil moist, but always let the surface dry out completely to prevent root problems.