Kilayim, Chapter 1, Mishnah 9. This mishnah deals with two entirely different subjects within the laws of kilayim. The first is a continuation of ideas mentioned earlier, that one may not mix a vegetable with a tree, meaning a vegetable together with a fruit tree, and this subject has implications for other areas of halachah as well. The second subject is the very heart of kilei zera'im: what is the definition of the Torah prohibition of kilayim.
"HaTomen lefes u'tznonos tachas hagefen":
This speaks of someone who buries, literally covers over, turnips and radishes beneath a grapevine. It does not refer to individual turnips or radishes, but to bundles and clusters of turnips and radishes that people would place in such spots purely for storage purposes. The purpose in placing them there was not for them to take root and grow, and that is why they were placed together in a single cluster.
About this the mishnah says: "Im hayu miktzas alav megulin" - if part of the leaves growing at the tops of the turnips and radishes are exposed and uncovered, so that they are not fully buried but only partially buried, this is not considered planting. And since it is not planting, there are ramifications for several halachos:
"Lo mishum kilayim" - he is not regarded as having mixed these vegetables, the turnip and the radish, together with the grapevine. There is no concern for kilayim, since there is no planting here at all, only storage.
"V'lo mishum shevi'is" - there is no concern regarding shemittah, neither from the standpoint of the prohibition to plant in the seventh year, nor if they should grow somewhat, the way onions sometimes continue to grow even after being uprooted from the ground. Even if they did grow a little, they are not considered produce that grew in the seventh year.
"V'lo mishum ma'asros" - regarding tithes too there is no concern for an obligation to tithe, and if they increased in size there is no need to be concerned about it.
"V'nitalin b'Shabbos" - one may even remove them from the ground on Shabbos, and this is not considered reaping, harvesting or detaching from the ground, since they are not growing in the earth but merely stored in it. The proof of this is that the leaves are still protruding and exposed.
Nor is there any concern that in taking them one moves a bit of the earth, which is muktzeh, because this is a case of gerama: the moving of the earth happens indirectly, through pulling the tips of the leaves, and it moves only the earth resting on top of the turnip and the radish. Moving something indirectly is not considered moving muktzeh, but only gerama.
Kilei zera'im from the Torah:
The second part of the mishnah deals with an entirely separate subject: mixing different species of vegetables and grains. The mishnah outlines the definition of kilayim on the Torah level, since a considerable portion of what is learned in Maseches Kilayim deals entirely with rabbinic prohibitions, situations that have the appearance of kilayim but are not kilayim of the Torah.
Kilayim of the Torah is as follows: one who sows a wheat kernel and a barley kernel at one time, placing them into the ground together - that is kilayim, and that is the Torah transgression. Not when they are sown side by side, but when the kernels are placed into the ground together.
Rabbi Yehudah has a variation on this, and in his opinion it is not considered kilayim on the Torah level except in one of these ways:
Two seeds of wheat and one seed of barley - one seed of wheat and one seed of barley is not enough.
Or alternatively the reverse: one wheat seed and two barley seeds.
Or three different types: one wheat seed, one barley seed and one spelt seed.
The reason Rabbi Yehudah holds that more than two species are required is the wording of the verse: "Sadcha lo sizra kilayim". Rabbi Yehudah understands from here that the term 'your field' applies only to a place in which something is already planted. Therefore one first needs a single seed to make the place a sown field, and in that sown field it is forbidden to make a mixture of two other species. It emerges that in his view three species are always required: the initial seed to render the place 'your field', and then the kilayim mixed into it.
The Sages, however, who said that two seeds suffice provided they are of two different species, hold that the place is considered a field even without anything having been sown in it. The ground itself is considered a field, and therefore no third seed is needed in order to transgress the Torah prohibition.
In summary: in this mishnah we learned two matters. First, one who buries turnips and radishes beneath a grapevine with part of their leaves exposed has not planted but stored, and therefore there is no concern for kilayim, shemittah or tithes, and they may be taken on Shabbos, even with regard to muktzeh, since moving the earth is no more than gerama. Second, the definition of kilei zera'im from the Torah: one who sows wheat and barley together, and the dispute between Rabbi Yehudah and the Sages as to whether three species are required because of the requirement that 'your field' be a sown field, or whether two species suffice because the ground itself is considered a field.