The grapefruit tree (Citrus paradisi) is the most frost-sensitive of citrus trees. Grapefruit trees, which can reach 22 to 30 feet at maturity, thrive in subtropical climates. Because the grapefruit tree is so cold-tender, select a planting site on the south side of your house to protect the tree from cold temperatures. Plant the tree about 12 feet away from the house so that the tree can receive full sunlight and to allow enough room for the grapefruit tree to grow.
Plant your grapefruit tree in a location that is slightly higher than the rest of your yard to ensure proper drainage. Plant the tree so that the bud union, or grafting bud, is above the soil level. Cover the top of the root ball with only 1 inch of soil to prevent root rot.
Make a water ring on top of the ground around the newly planted grapefruit tree by constructing a 3-inch ridge of soil 2 feet in diameter. Fill the inside of the ring with water and allow it to drain into the soil around the root ball.
Water your grapefruit tree once every two or three days for the first three weeks after planting. Gradually decrease the frequency of watering to once every 7 to 10 days during the first growing season.
Feed your grapefruit tree during the first year only after new growth emerges. Fertilize with 1 cup of ammonium sulfate (21-0-0) divided into three or four applications during the growing season. Spread the granular fertilizer on the ground around the root zone of the tree and water thoroughly.
Keep a 2- to 3-foot area around the base of the grapefruit tree free of weeds. You can pull the weeds by hand or apply a selective herbicide according to the directions on the label.
Feed your grapefruit tree again in the second year with 2 cups of ammonium sulfate in the spring. Fertilize the tree in the third year with 3 cups of ammonium sulfate.
Water your grapefruit tree once every one or two weeks during the second growing season and thereafter. Water the tree deeply, soaking the soil down to the entire root zone.
Feed adult grapefruit trees 1 cup of ammonium sulfate for each year of age, up to 6 cups. Spread out the fertilizer feedings into three separate applications, in February, May and September.
Protect your grapefruit tree whenever freezing temperatures or frosts threaten. You can drape a blanket or tarp over the tree and secure the edges to the ground with stakes.
You also can mound up soil around the base of the tree to insulate the roots. Mound up the soil in late November and remove it in early March.