The key lime tree (Citrus aurantifolia "Swingle") is a small, bushy tree that will grow to a height of 12 feet. Grown from seed, the key lime bears fruit in six to seven years while a grafted tree will grow fruit within three to four years. The key lime tree is cold-intolerant and must be grown in soil with good drainage. Start your key lime seeds in late winter or early spring.
Fill the planting pot with seed starting mix, to within 1/2 inch of the top of the pot. Saturate the soil with water and allow the pot to drain completely.
Push the key lime seed 1/4 inch into the soil and cover it lightly with soil. Do not press down on the soil covering the seed.
Place the pot on the heat mat, set to 75 degrees F. and then place it in a sunny area. Keep the soil moist while the seed germinates, which should occur within two to three weeks. Turn off the heat mat at that time, and allow the lime seedling to remain in a sunny location.
Repot your lime seedling into a 8-inch pot when it reaches 4 inches tall. Use equal parts of sand and potting soil and place the roots at the same depth at which they were in the smaller pot. Allow the top inch of soil to dry between waterings.