Grafting pecan scion onto an oak tree outside of Israel
Question
I live in the Diaspora. I have three mature Burr Oaks growing in the front of my property which give a lot of burr acorns. They are edible, though we do not eat them. My property is too small to add pecan trees in it, and I do not wish to destroy good trees. Is there a halachic way to graft some pecan branches onto the burr oaks in order to yield pecan nuts?
Answer
A burr oak is considered a non-fruit-bearing tree (etz serak), since we do not eat its fruit. Even if theoretically its fruit (=the part with seeds) is edible, most people do not eat acorns today, so it is considered a non-fruit-bearing tree. Pecan trees, in contrast, are certainly fruit trees. If we are to say that acorns are eaten by people (as they were by Native Americans and in Korea, even today, for example), and that oaks would thus be considered fruit trees, the prohibition would then be more severe. This is because the graft would be of two dissimilar species, min beshe-eino mino, which is a Torah prohibition according to all opinions.
Grafting a fruit tree onto a non-fruit-bearing tree
The Yerushalmi (Kila'im 1:7) writes that it is forbidden to graft a fruit tree onto a non-fruit-bearing tree: "What is the source that we do not graft a non-fruit-bearing tree onto a fruit-bearing tree, nor a fruit tree onto a tree bearing edible fruit? What is the source for [the prohibition against grafting] unlike species onto one another? It is stated: 'You shall observe my decrees' [Vayirka 19:19]."
A non-fruit-bearing tree is considered its own species, distinct from fruit tree species. Note that it is permitted to graft different non-fruit-bearing trees onto one another, since halachically they are considered the same species. In contrast, grafting one type of tree (here: fruit and non-fruit bearing) onto another is considered grafting dissimilar species (min beshe-eino mino) and is thus forbidden. This is the ruling of the Shulchan Aruch (YD §295:3). Albeit there is a dispute whether this type of grafting is a Torah or rabbinic prohibition.
Is it permitted for a Jew to commission a non-Jew to perform a forbidden graft?
Rambam (Kila'im 1:6) writes: "And it is forbidden for a Jew to allow a gentile to graft trees of different species onto one another." Also in Hilchot Melachim (10:6), Rambam states: "It is a tradition [from our Sages] that the Noahides are prohibited to cross breed animals as well as to perform forbidden grafts of trees." Shulchan Aruch rules similarly (YD §295:2): "It is forbidden for a Jew to allow an idol worshipper [i.e. = gentile] to graft trees of different species."
Why not—kila'Im is not one of the seven Noahide laws?
In truth, there is a Tannaitic dispute on the matter; Rabbi Elazar holds that Noahides are obligated by the kila'im prohibition, while the tana kama (the first opinion stated in the mishna) exempts them.
Some hold (Kesef Mishne, Kila'im 1:6; Chazon Ish, Kila'im 1:1) that we follow the tana kama, and that gentiles are permited to graft different species onto one another. However, miderabanan, we may not ask the non-Jew to perform what is for us a prohibited act (as a statement to a gentile, amira lagoy).
Others (Mishne Lamelech, Kila'im 1:6; Gra YD §295:4) hold that we rule according to Rabbi Elazar, that grafting is included in the Noahide laws and is biblically prohibited to non-Jews. For this reason, it would be forbidden, mide'oraita for us to ask gentiles to perform a forbidden graft so as not to "place a stumbling block before a blind person" (that is, to cause him to transgress).
That is, according to all of the opinions, it is forbidden to ask a non-Jew to perform a forbidden graft on a Jew's behalf.
On the other hand, if there is a doubt regarding the forbidden status of the graft, it is permitted to commission a gentile to perform the graft (Chazon Ish, Kila'im 1,1; 3,12). In the case at hand, however, there does not seem to be any doubt in the matter.
There are some who permit (Chatam Sofer YD §288, Aruch HaShulchan YD §295,16-18) to sustain a tree grafted in a forbidden manner outside the Land of Israel, after the graft fuses, when the graft is performed by a non-Jew. However, this opinion contradicts the Shulchan Aruch, which prohibits this. There may be room to be lenient only in exceptional cases.
Grafting outside the Land of Israel
The Gemara (Kiddushin 39a) states explicitly that kilei ilan is prohibited outside the Land of Israel. This is also clearly stated by the Shulchan Aruch (YD §295:1): "One who graft a tree onto another tree … is liable for lashes from the Torah everywhere, whether in the Land of Israel or outside the Land of Israel."
Grafting a pecan onto an oak tree: a botanical perspective
I consulted with the agronomist of Torah VeHa'aretz Institute, Dr. Mordechai Shomron. He said that from a purely botanical perspective, there is a very slim chance that such a graft would succeed.
In conclusion:
Pecan shoots should not be grafted onto oaks, even outside the Land of Israel. It is even forbidden to commission a non-Jew to perform the graft.