Pour potting mix into a container, such as a bucket, adding enough water to moisten the mix. Never make the mix soggy or muddy. Stir the mix and the water with your hand or a spoon to thoroughly combine.
Fill the jar two-thirds of the way to the top with potting mix.
Place the lily bulb into the mix, with the pointed tip facing up. If there are any roots on the bulb, arrange them so that they lie flat on top of the potting mix.
Cover the bulb with more potting mix, filling the jar the rest of the way to the top.
Water the bulb in the jar and place it in a warm room to begin growing. Calla lilies won't stop growing at a temperature below 55 degrees Fahrenheit.
Place the lily in a well-lit spot once it begins to grow leaves and stems.
Water the lily daily. Calla lilies prefer very wet soil once they sprout and a glass jar is ideal for holding that moisture in until the next day's watering.