As noted, although one may not graft two tree species together, the fruit produced by such grafting is permitted from the outset. The practical question is what may be done after a prohibited act of grafting has already been performed. May one care for the grafted sapling and water it so that it continues to grow? This question arises frequently. Most pear trees, for example, are grafted in a prohibited fashion, and prohibited grafting is also common among plum and peach trees. The question, then, is whether one may plant a sapling that was produced through prohibited grafting in a nursery. If it has already been planted, may one continue caring for it, or must it be uprooted?
Some maintain that the prohibition is limited to grafting two different species together. Once the graft has been made, however, there is no further prohibition against maintaining the grafted tree. Therefore, if a sapling was grafted in a nursery, one may even plant it in the field and tend to its growth. According to this view, tree grafting is similar to animal kilayim: the prohibition is only to breed an animal of one species with an animal of another. Afterward, however, one may raise and use the offspring.
Many poskim, however, rule that one may not maintain a grafted tree (SA YD 295:7). They disagree, though, about the scope of this prohibition. According to one view, one who has a grafted tree in his field must uproot it. According to another, one may not weed around it or prune it to improve its growth but may leave it in the field untended. A third view maintains that the prohibition applies only until the rootstock and scion have fused. Once they have fused, one may maintain the grafted tree and even plant it.
In practice, some rely on the lenient view that the entire prohibition is limited to the act of grafting. According to this position, even before the graft has fully fused, one may plant the grafted sapling and tend to its growth. The halakha, however, follows most poskim: one may not maintain the grafted sapling until the graft has fused. After that point, one may plant it and care for it. Ideally, one follows the stringent view and refrains from maintaining a grafted tree even after the graft has fused. When there is uncertainty whether the grafting was prohibited – that is, whether it involved two distinct species, or was permitted because it involved two varieties of the same species – one may be lenient and maintain it.
When purchasing a fruit tree, one must verify that it was not grafted in a prohibited manner. Even according to the lenient authorities who permit planting a grafted sapling, buying from someone who performs prohibited grafting assists those who violate the prohibition. Since these laws are complex, one may rely only on a seller who is both knowledgeable in these laws and God-fearing, or on a nursery under reliable kilayim supervision.[6]
[6]. According to the lenient authorities, maintaining a grafted tree is not prohibited. This is the view of Ritva (Kiddushin 39a), Orḥot Ḥayim, and Radbaz. Many understand Rambam similarly. R. Herzog writes that this is the view of most Rishonim, and therefore one may rely on this view in pressing circumstances (Teḥumin 5; see also Shema Shlomo 3, YD 11). Some ruled that ideally, such trees should be cared for by a gentile until the graft has fully fused (Yabi’a Omer 10, YD 36).
By contrast, some prohibit maintaining a grafted tree. This is the view of Rosh, Laws of Kilayim §3; Rabbeinu Yeruḥam; Tur; and SA YD 295:7. However, there are three views regarding the scope of this prohibition: 1) According to many, the prohibition against maintaining the tree continues only until the graft has fused. Afterward, there is no prohibition against maintaining the tree. This is the view of Ḥatam Sofer 6:25; Arugot ha-Bosem YD 233; Maharsham 1:179; and Arukh ha-Shulḥan YD 295:18. R. Herzog writes that according to this view, one may also plant a sapling that was grafted in violation of the prohibition in the ground once it has fused. Rav Kook inclined toward this view as well (Mishpat Kohen 14–15). This is also the view of most halakhic decisors (R. Goldberg, Teḥumin 5). 2) According to another view, one may not care for a grafted tree, but if it has already been planted, one may leave it in the field. This is how R. Z. Guta and Mishnat R. Eliezer 2, YD 51, explain this view, though they themselves inclined toward the lenient position of Ritva and those who agree with him. 3) According to a third view, one must uproot the grafted tree. This is the view of Ḥida in Birkei Yosef 295:7 and Divrei Yosef 24, and many authorities mention this position. This is also the view of Ḥazon Ish (2:9). He adds that when there is uncertainty whether the grafting was prohibited, one may be lenient and care for it on the basis of a safek sefeka, a double doubt (Kilayim 1:1; 2:9; 3:3). If we follow Levush, who maintains that even the prohibition against maintaining a grafted tree is Torah law, this is a Torah-level doubt, and one may not be lenient without a safek sefeka. By contrast, R. Herzog writes that even according to those who prohibit maintaining the tree, many maintain that the prohibition is rabbinic. Accordingly, the halakha follows the lenient view.
In practice, one should ideally not maintain a grafted tree. In cases of need, however, the ruling follows Ḥatam Sofer and those who agree with him: once the graft has fused, there is no further prohibition. If possible, it is preferable for a gentile to plant it (Hilkhot ha-Aretz, Kilayim 8:11–13; Kedushat ha-Aretz 18:25–28).
