Summary:
People are never טומן בסלעים since they break the pots. Either it is אסור להטמין בסלעים, but the משנה does not mention it since it is לא שכיח, or since it is לא שכיח it is מותר להטמין בסלעים. Alternately (ר"ת) the סלעים ruin the food in the pots (like rust ruins the metal). Finally (ר"י ור"ח), רבא is explaining our משנה that סלעים must be distanced because they ruin the earth, but no heat.
Summary:
By a lone grapevine there is no concern of יניקה, only for ערבוביא. There is a concern for הרכבה from seeds by a גפן since its vines and roots are soft.