Place the shamrock in a room with daytime temperatures of 75 degrees Fahrenheit or less and nighttime temperatures 10 to 15 degrees cooler. Be sure the temperature doesn't drop below 40 degrees Fahrenheit.
Water the shamrock whenever the top of the soil feels slightly dry. Add water slowly until it begins to trickle through the drainage hole, then let the pot drain thoroughly. Never let the soil remain soggy or waterlogged.
Fertilize the shamrock lightly once every month while the plant is actively growing. Use a regular house plant fertilizer with a balanced ratio such as 15-15-15. Mix the fertilizer at a rate of ¼ teaspoon per gallon of water.
Stop watering and fertilizing if the leaves begin to die back during the summer months; shamrock benefits from a period of dormancy. Put the plant in a cool, dark place for two to three months, or until new growth emerges.
Cut back the foliage on potted plants to within 1 inch of the soil after the leaves begin to brown and die back during early summer. Stop watering and store the plant in a cool, dark place for two or three months.
One reason why your plant's leaves may turn yellow is because you are over-watering the plant. A shamrock plant that cannot absorb iron suffers from chlorosis, which causes its leaves to develop yellow spots.