Grafting several types of citrus fruit onto one tree

Answer

It is forbidden to do so, even by poskim who are lenient about having citrus trees grafted and planted by a non-Jew, as is standard practice today. The lenient opinion about grafting different citrus trees is relevant only when it is not apparent that the scion is from a different species than the rootstock. It is forbidden to cross lemon and orange trees due doubt—safek mino—which is why lenient poskim hold that it is possible to tend to such trees.

In the case at hand, one sees three types of fruit on one tree, so this is a much more serious form of grafting. It is forbidden even to commission a non-Jew to perform this sort of grafting on one’s behalf.