With the beginning of the seventh perek, a new case of kilayim relating to vineyards is introduced – bricha. A method of propagating vines is to bury a branch from an existing vine leaving it connected while letting a sprig of leaves to be exposed. The buried section will take root and that buried branch can be cut from the original vine leaving a new young vine. The Mishnah (7:1) teaches that if the vine is buried at a depth of three tefachim then one is allowed to plant produce in that soil. Alternatively, if the branch is surrounded by an impenetrable casing, eg rock, then one can plant in the soil above it. What are the concerns in this case behind the ruling?
The first point that must be made is that the Mishnah is dealing with a case where the grain is not being planted inside avodat gefen – the six tephachim area around a single vine. Planting within that area would constitute kelei hakerem regardless of any buried branches.
Rabbeinu Gershom (Bava Batra 19a) explains that if the branch is buried to a depth of less than three tephachim then the roots of the grain will reach the branch and the two would draw nourishment from one another. In such a case the prohibition of kilei ha’kerem would be violated.
The Tosfot however raise a difficulty with this understanding. We learnt earlier that a ten tephachim high fence constitutes a satisfactory separation between a vineyard and a field of grain. In such a case the regular distance between them is not required. because above the ground the mixture is not visible. This is despite the fact that under the ground they may be drawing nourishment from one another.1
Consequently, the Tosfot argue that in this case kilei ha’kerem is not the issue. Instead the concern is that the roots of the grain will enter the buried branch. This would constitute the broader prohibition of grafting. If that is the case, why then does the Mishnah discuss vines? The prohibition applies to all fruit trees! They explain that there is a greater concern for vines since they are softer.
A difficulty with this explanation arises in the next Mishnah. R’ Elazar bar Tzadok teaches that while it is prohibited to plant grain in our case, if one does so, the grain does not become assur. The Rambam rules that the halacha does not follow his opinion. The Shoshanim Le’David asks that the Rambam seems to imply then that the grain is also assur. If the concern involved is grafting then the grain would not be assur. The Chazon Ish notes that this would seem to suggest that prohibition involved is indeed kilei ha’kerem.
The Chazon Ish answers that one can understand the position of the Rambam even according to those that maintain that the concern is only because of grafting. He explains that even though because the mixture is not visible there is not prohibition of kilei zerayim, once the seeds take root in the branch and become one underground, that this is a different story – it becomes kilei zerayi and the produce would then become assur. This also appears to be the explanation of the Pnei Moshe (Yerushalmi 7:1): “… therefore we require three tephachim above the vine, so that the seeds do not penetrate the vine, and become kilei ha’kerem.”
1 The Rash argues similarly based on Mishnah (1:8).
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