הלכה על קידושין 112:21

From the laws of the commandment is that which they, may their memory be blessed, said (Menachot 15a) that the Torah's prohibition of a forbidden mixture of the vineyard is only in the case of types of grain and hemp and arum, but to plant vegetables and other types and grape-seed is [only] forbidden rabbinically. And so [too] did the Rabbis forbid to plant types of grain and also vegetables alongside the grapevines, or to plant a grapevine alongside the vegetable or the grain, because of the concern of interbreeding. Since the grapevine is softer than all other trees, they were more concerned about it. And if he did this - even though he is not lashed - behold, he set [it] apart and it is forbidden to benefit from both of them, and we burn the whole thing. And [we burn] even the chaff of the grain and the wood of the grapevines, as it is stated, "lest it be set aside (tikdash), the crop, the seed, etc." - and they, may their memory be blessed, expounded (Kiddushin 56b), "Lest it be incinerated by fire (tukad esh)," meaning to say that all of it is fitting to be burnt, as we will write adjacently (Sefer HaChinukh 449). And the rest of its details are elucidated in Tractate Kilayim (See Tur, Yoreh Deah 246).

To not eat forbidden mixtures of the vineyard: That we are forbidden from eating forbidden mixtures of the vineyard only. And we have already explained in the previous commandment what forbidden mixtures of the vineyard are. And about this is it stated (Deuteronomy 22:9), "lest it be set aside (tikdash), the crop, the seed that you planted and the produce of the vineyard." - and they, may their memory be blessed, explained (Kiddushin 56b), "Lest it be incinerated by fire (tukad esh)," which is to say that it is not fitting that there be a purpose [from it], as it should all be forbidden in benefit. And the proof that there is a negative commandment in it, is that it is written in its prevention, "lest (pen)." And they, may their memory be blessed, said (Eruvin 96a) that in every place that it states, "guard yourself," "lest," and "do not" (heeshamer, pen ve-al), it is certainly a negative commandment.