The Rabbis derive the prohibition against creating new fruit varieties by grafting branches of one type onto the tree of another type from the comparison of kilayim of animals to that of plants.[2] Whereas the Torah instructs man to harness the world for his needs,[3] there are limitations on meddling with the natural order of creation, which lie at the heart of the laws of kilayim.[4] Halacha teaches us which actions are forbidden and which are permitted. It also teaches us the repercussions of forbidden actions, including grafting. We are not required to boycott when the Torah and the Rabbis did not take the prohibition that far.
There are two main halachic elements that relate to distancing oneself even from someone else’s aveirot.[5] In some cases, we may not eat a food that was produced or processed in a forbidden manner (e.g., food that was cooked on Shabbat), at least to a certain extent.[6] Sometimes it is forbidden even to benefit from the food (e.g., milk and meat that were cooked together or a vineyard that was involved in kilayim).[7] The gemara[8] derives from p’sukim that neither eating nor deriving benefit is an issue for kilayim that do not involve grapes. Indeed, the same Torah that forbids grafting permits eating or selling the resulting fruit.
Another element in staying away from the aveirot of others is prospective; it is forbidden to proactively facilitate (lifnei iver- forbidden from the Torah) or even aid in (m’sayeiah- from the Rabbis) aveirot. However, these laws do not create prohibitions post facto. We do not find, in this regard, prohibitions that are motivated by a concern for retroactively justifying the aveira or allowing the sinner to profit.
The feeling of disapproval about the existence of fruit that should not have been produced is discussed regarding the beracha of Shehecheyanu. Reciting that beracha may imply that we are happy the fruit exists.[9]
Now that we are confident that a halachic prohibition to eat the grafted fruit does not apply, let us investigate the question of trying to limit these aveirot by means of a boycott. This is pertinent on a public scale in Israel, where the religious community makes up a sizable share of the market. Might a boycott affect how much grafting will occur in the future? While we cannot give a thorough answer to this question, let us point out that it is unclear how many farmers from whom we buy fruit are sinning. We will introduce some factors, but we will not rule when a given farmer can actually rely upon them. (You have asked us to address consumers, who do not really have a halachic problem.)
Kilayim is not one of the seven Noahide laws. Yet, the Rambam[10] says that a Jew may not let a non-Jew graft onto his trees. Commentaries[11] disagree as to whether this is because there is a lower level prohibition for a non-Jew to graft or because a Jew may not ask a non-Jew to do something that is forbidden for Jews. In any case, if a non-Jew does the original grafting, there is more room for leniency. Regarding more severe forms of kilayim, one may not sustain the kilayim as it grows. Although it is less clear whether grafting is in that category, we rule stringently.[12] Yet, the Chatam Sofer[13] says that once the grafted branches are no longer recognizable as such, these halachot cease to apply. The Rambam[14] and Shulchan Aruch[15] agree that one may cut off a shoot from a grafted tree and plant it as a new tree. Furthermore, poskim point out that since grafting is forbidden only between two species, it is not always obvious which of our modern applications involve halachically distinct species. A summary of the practices that rabbis permitted to religious farmers in Eretz Yisrael can be found in Rav Yisraeli’s work Eretz Hemdah.[16]
In conclusion, a consumer may eat grafted fruit. In fact, most farmers who grow the fruit have grounds for leniency due to a combination of factors.