Q. I started a grapefruit tree from seed as a kindergarten class project about 50 years ago. The tree is thriving but has never borne fruit. Why?

A. There could be many reasons, especially if the tree remains mostly indoors.

The grapefruit was first described growing in Caribbean islands in the 18th century. It is now believed to be an accidental hybrid of the pummelo, the largest citrus fruit, and the orange.

Getting a grapefruit tree to grow in a container is not hard; it is more difficult to duplicate the semitropical conditions that are best for blooming, pollination and fruit development.

An indoor tree may not receive enough direct sunlight to thrive. Even when sunlight is adequate, a difference of 10 to 15 degrees Fahrenheit between daytime and nighttime is most conducive to flowering.

If there are blooms, a citrus tree may pollinate itself to some extent. But for more than 10 to 15 percent of the blooms to be pollinated, bees are required.