The grapefruit tree (Citrus paradisi) can reach 15 to 20 feet in height and generally has very long thorns. Since they normally grow best in warm, subtropical climates, you will need to adjust the indoor environment in order to be successful with the grapefruit tree as a houseplant. Cooler indoor temperatures will signal the tree to go dormant. It is easy to grow a grapefruit tree from the seeds of the grapefruit.
Clean all the fruit pulp from the seed by gently rubbing it under running water.
Fill a small bowl with room temperature water and drop the seed into the water. Allow it to soak in the water overnight.
Fill the planting pot with moist potting soil and insert the grapefruit seed 1-inch into the soil. Cover the seed with soil and place the pot in an area with lots of light, but out of direct sun. Water it enough to keep the soil moist but not soggy.
Transplant the seedling when roots appear at the bottom of the pot. When transplanting the grapefruit tree, always use a pot that is 2 to 4 inches inches larger than the original pot. Fill the new pot with moist potting mix and dig a hole large enough to accommodate the grapefruit seedling's roots. Carefully remove the grapefruit seedling from its current pot, place the roots into the prepared hole in the new pot's soil and pack soil around the roots.
Place the newly potted seedling in an area where it will receive lots of light (no direct sun). Repot the grapefruit tree again when roots become apparent at the bottom of the pot, through the drainage holes.