Pollination in citrus trees is a simple and straightforward matter. The fluffy, yellow pollen produced by the male parts of the blossom must come into direct contact with the female parts of the flower to produce a single fruit. The typical indoor home environment lacks the plant's natural pollinators--bees and adequate air circulation. These conditions can easily be simulated to pollinate the indoor lemon tree. The petals will fall off as the successfully pollinated blossom develops into an ovary, which eventually will grow into a lemon.
Identify male and female parts of the lemon tree. The female stigma is the sticky structure in the centre of the flower. Multiple long filaments surround it with visible fluffy, yellow pollen grains on the ends. These are the male parts, or anthers.
Gather some fluffy yellow pollen from the anthers of the blossom, using a cotton swab, small soft paintbrush or the tip of a finger.
Dab the pollen directly onto the stigma. Make sure some of the pollen adheres to it.
Repeat the hand-pollination with each bloom you wish to develop into a lemon.
Place the indoor lemon tree in a warm room, such as next to a window with southern exposure, where it will receive as much direct sunlight as possible. Eight to 12 hours of strong natural daylight is perfect. Ideal temperature is at least 21.1 degrees Celsius during the daytime and no lower than 12.8 degrees Celsius at night.
Water enough to keep the soil evenly moist, but don't allow it to become soggy or wet. Mist the indoor lemon tree daily to provide humidity.
Feed your lemon tree a good slow-release granular 2-1-1 fertiliser for citrus plants every three months throughout the year. Follow the packaging instructions carefully.