To grow a lemon tree from seed, remove the seeds from a fresh lemon. Rinse the seeds with lukewarm water, rubbing away their slimy coating, and allow them to dry for a week. Plant the seeds 1 inch deep in 3-inch peat pots filled with well-watered and drained potting soil.
Lemon seeds need warmth to germinate, so cover the pots with a sheet of plastic wrap and set them on top of a warm surface. When the seeds begin germinating, remove the plastic from the pots with seedlings and move them to a sunny window for a minimum of five hours per day. Once the roots of a seedling begin coming through its peat pot, plant the seeding, pot and all, in sterile potting soil in a larger pot that is at least 8 inches tall by 8 inches wide. After planting, water until the soil is moist. As the lemon tree continues growing, transfer to larger pots as needed.
To grow well, lemons need temperatures of about 70 degrees Fahrenheit during the day and 55 degrees at night. Keep the soil evenly moist, and fertilize as needed. During the winter, the gardener may need to use a fluorescent grow light to keep the plant thriving. In the summer, set the tree outside to increase the chances of pollination and fruit bearing.