Citrus trees like grapefruit make for unique, exotic house plants. If you can provide enough sunlight, fertilizer and proper temperature control, you may even get sweet smelling flowers and delicious fruit from your indoor grapefruit tree. You can grow a tree from a seed from a grapefruit from the grocery store, but you'll get quicker results with a potted grapefruit plant purchased from a nursery.
Start a grapefruit seed by placing it in a loosely closed plastic bag with some damp peat moss. Place the bag in your refrigerator for three to four weeks, and then plant the seed in a small container (6 to 8 inches in diameter) filled with potting soil. Keep the soil moist but not waterlogged. The seed should germinate within a few weeks.
Choose a grapefruit tree from a nursery. Citrus trees are generally not sold bare root, so the trees will be potted in soil and they should have lush green leaves and vigorous growth. Younger trees may have spikes on them. Look for a dwarf variety that is better suited to being grown indoors.
Allow your indoor grapefruit to get plenty of light. A south or west facing window is best. A citrus tree can adapt to lower levels of light, but it won't flower or set fruit.
Water your grapefruit tree only when the soil is dry to the touch. Overwatering a grapefruit tree may cause the roots to rot.
Maintain healthy humidity levels. In the winter, many homes get too dry for citrus trees to thrive. Running a humidifier will keep your grapefruit tree happy.
Provide your grapefruit tree with the temperatures it needs. Grapefruit trees require a period of cold to trigger blossoming, followed by a long period of intense heat. This can be accomplished by moving your grapefruit tree to an enclosed, unheated sun porch in the winter, and then to a warmer location during spring and summer. Do not allow your grapefruit tree to be exposed to temperatures below freezing. Once the fruit forms, it may take a full year or more to ripen, so be patient and keep your grapefruit in a warm and sunny location.
Apply fertilizer according to the package instructions. Look for a product that is specifically formulated for citrus trees.
Move your grapefruit outside during the summer if you can. It will benefit greatly from the fresh air, sunlight and, if it's flowering, access to pollinators.
Pollinate grapefruit flowers by hand if you cannot move your plant outside. Use a small paint brush or a cotton swab to touch the center of each flower to transfer the pollen. You do not necessarily need two trees for adequate pollination, but it might improve your chances.
Repot your grapefruit tree once a year. Grapefruit may suffer if they are planted in too large a container, so choose a new pot that is only 3 or 4 inches wider in diameter than the old one. Do not repot a grapefruit tree that has flowers or fruit on it.