Tending to an apricot tree grafted onto an almond scion

Answer

There are two types of forbidden grafting, for which the issue of if it is permitted to tend) to them (kiyum) is different from a halachic perspective.

1. A regular graft done in a forbidden manner. That is, when one species is grafted onto a different species, whereas the bottom tree does not bear fruit at all, and just serves as a strong rootstock that withstands soil maladies and repels pests better than the scion (branch grafted on). On top of this rootstock is grafted a scion from a different species that bears fruit that is tastier. For such grafts, the Shulchan Aruch rules that it is forbidden to tend to these trees.

Some Acharonim (Aruch HaShulchan, Chatam Sofer), however, in contrast to the straightforward understanding of the Shulchan Aruch, write that the prohibition of tending to the tree (kiyum) relates only to the case where the graft has not yet fused together. But once the scion and rootstock have fused together into one trunk, the prohibition of tending to the tree no longer applies. For this reason, since the tree has already been grafted and planted, in extenuating circumstances and when needed we can rely on these opinions to continue tending to such trees, when taken together with the opinions of several Rishonim, who rule that there is no such prohibition of grafting trees; while there is a Torah prohibition of uprooting fruit trees (see Responsa Be’ohala Shel Torah IV §31).

2. However, there are situations in which on the same tree two scions from two different trees yield fruit simultaneously, since it is aesthetically beautiful; but the halacha doesn’t see it this way. In such cases, Rabbi Shaul Yisraeli ztz”l rules that it is prohibited to tend to such trees, and that one of the species should be cut down, while leaving the other (Eretz Hemdah Kila'im II; see also Hilchot Ha'aretz, p. 180).