Q.Growing a grapefruit tree from root of mature tree
I have what appears to be a young grapefruit tree growing from one of the roots of a mature grapefruit tree – about 12 feet from the trunk. Will this young tree grow and produce fruit of its own? Can it be dug out and transplanted? Can I graft an orange tree branch to it?
You can try to repot or move the growth. Either way it is best to remove this growth as it is likely taking energy from the tree.
Keep in mind that the new tree may not be the same as the mother tree. It is likely some citrus variety.
Here is a link with more information.