Yerucham from Neve Ya’acov asks:
A tomato plant has recently started growing out of our concrete garden
path. Are these tomatoes permitted or do they fall under the category of s’fichin?
At this time of year, all tomatoes grown on Jewish-owned land
are forbidden because of s’fichin. Even if they grew spontaneously (for
example, from tomato seed which scattered in the wind) they are still forbidden.
However, our Sages did not apply the prohibition to (a) species which are not
usually cultivated or (b) places which are not usually cultivated. Thus, wild
edible plants found growing in a forest are not subject to this prohibition.
Similarly, if plants suddenly sprout of a concrete path or yard they are also
permitted, even if the species is generally cultivated. Not only may you eat the
fruits of your tomato plant, but you can also water the plant and perform
whatever rabbinically-prohibited work is required to keep it alive. The tomatoes
obviously have kedushas shvi’is.