Composting terumah and using compost as fertilizer

Answer

It is forbidden to render terumah tameh (ritually impure), to destroy it, or to cause its loss.¹ As it says in the verse (Bamidbar 18:8): “And I have given you the charge of My terumah.” Likewise, the Rambam rules (Hilchot Terumot 12:1): “It is forbidden to render terumah of the Land of Israel tameh like other kodashim, and one must not bring it to tumah nor cause it to be destroyed.”

It is also forbidden to cause the loss or impurity of terumah indirectly. According to some posekim, gram hefsed (indirect loss) is prohibited by Torah law, while others hold that it is only rabbinically prohibited.²

The question arises regarding pure terumah today, when kohanim are impure and may not eat it. According to Rabbi Kook,³ even today there is a mitzvah to preserve pure terumah so that it does not become ruined; therefore, it should be left to decay on its own.⁴

However, according to the Chazon Ish,⁵ one may bury it to prevent mishap—that someone might accidentally eat from it—even though this constitutes gram hefsed.⁶ For this reason, he permits the same practice with terumah teme’ah (impure terumah) nowadays, even though strictly speaking it is a mitzvah to burn it.⁷

The common custom follows this view: after reciting the formula for separating terumot and ma'aserot, the terumah and terumat ma’aser fruits are wrapped in a plastic bag, whether the  terumah is pure or impure, and then placed in the garbage bin in such a way that they are not mixed with the rest of the trash.

Conclusion

Based on this, one may place terumah fruits in a compost bin, provided they are first wrapped in a paper bag and only then put into the compost bin. Although at some point the paper will decompose and the terumah will mix with the compost, by then the fruits will have already decayed and will no longer be fit for human consumption, so the terumah will no longer be sacred.⁸ Therefore, the resulting compost may be used to fertilize the garden.