Grapefruit trees are evergreen subtropical citrus trees that grow up to 50 feet tall in some cases. These trees produce bitter, juicy fruits with yellow skins. Grapefruit is hardy in USDA zones 9 to 11, which means you can grow it outdoors in regions where the temperature does not drop below 20 degrees Fahrenheit. Knowledge of how to create the right environment for the plant will help you produce a thriving harvest.
Plant the grapefruit tree in an area with full sun and deep, well-drained, loamy soil. For the best winter protection, plant the tree on the south or southeast side of a building. Leave 12 feet between the grapefruit and any buildings or sidewalks to allow the tree to grow to maturity.
Water every few days for the first couple weeks, keeping the soil moist but not soaked. Over the next few months, decrease watering frequency to once every seven to 10 days. Once the tree starts growing vigorously on its own, it will require a deep watering once every two weeks at most.
Weed around the tree, eliminating any competition for the grapefruit. Keep the lawn grass away as well.
Fertilize after growth commences with 1 cup of ammonium sulfate split into three applications. For each year after that, apply 1 cup of fertilizer per year of tree age. For example, if the grapefruit is 6 years old apply 6 cups of fertilizer split into three applications (eg. 2 cups in February, 2 cups in May and 2 cups in September).
Protect the tree from cold, especially if a frost is predicted. For quick coverage, throw a blanket or tarp over the top of the tree and stake the corners. For more complete protection, mound up dirt around the base of the tree.