I have a 3 year old avocado tree about a meter and a half high. I planted it from a seed of an avocado I ate. I was told I need to graft it for it to hold fruit. What kind of graft should I do? What time of the year? Thank you :)
The trouble is, you need a scion that produces good fruit to graft to the plant you have growing - the rootstock for grafted avocados is what is produced when you grow from a seed in the way you describe. I'm not at all sure where, or even whether, you could source the scion necessary for the grafting procedure, but how to do it is described here http://homeguides.sfgate.com/graft-avocados-37523.html
If you know someone who has an avocado that produces good fruit, you could possibly try using a branch from that to create your scion, and try grafting that to your avocado plant, but you'd need to select something that is of equal girth to the part of your avocado where you want to make a graft so that the vascular tissue joins together well.
Is it in the ground ?, if not take it and the pot to a tree that fruits and graft it like this: I'm not sure what the technical name for this graft is but that's probably your best bet at success without risk killing the seedling. https://youtu.be/hTmlio-4i5M
If you are doing a graft with new budwood / scion it has to be done at a particular time of year, as for the graft I posted above I'm Not sure.