Citrus combination?
 

I got a grapefruit tree some years ago. I had not much time for the garden
then, and it was neglected (even though it gave a few grapefruits in the
beginning - nothing since).
Now I have more time, and have moved it to a better position. After a year, it
is quite vigorous - but no flowers at all, even though the other trees all have
lots.
Maybe the implant has died and just the rootstock survives? It would be a pity
to waste that sturdy little plant: is it possible to implant another citrus (eg
tangelo Minneola) on the trunk?
If so: where to find instructions and any material needed?

Regards,
Occam
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