To grow a lemon tree from seed, first, extract seeds from a ripe lemon. Rinse them to remove any pulp. Plant seeds in a small pot filled with well-draining soil, about ½ inch deep. Keep the soil moist but not waterlogged. Place the pot in a warm, sunny location. Germination may take several weeks to months. Once sprouted, transplant the seedling to a larger pot. Provide regular watering and sunlight, and your lemon tree will thrive.