I have a mystery citrus tree that bears sour and almost inedible small oranges. This tree is about 10 years old. I'd like to cut-off its branches and graft on branches from a Navel or Valencia orange tree. Is this possible?
If that is possible then is it also possible to graft two different types of tree onto the stem of one tree such that it bears two different types of fruit?
Yes and yes. It sounds like you have a sour orange which is typically used as root stock for full sized citrus trees. You can graft grapefruit, orange, lemons and limes to this stock. Oranges and grapefruit will do the best. If you put Mexican lime on one side and grapefruit on the other the lime side will grow slower and the grapefruit side faster and so you will get a very strange looking tree eventually. However, if you try some Valencias, navels and blood oranges the growth will be more proportionate. If the stock is more than a few years old you will use top working techniques - probably cleft grafting would be best. If you go to Texas A&M's website you can get some in depth instruction on how to do it. Here is an article on cleft grafting at the A&M site: http://aggie-horticulture.tamu.edu/propagation/cleftgrafting/cleftgrafting.html
