(Mishnah): If a field was sown and he then decided to plant saplings, he shouldn't say that he will first plant and then overturn the soil with a plow; he should first overturn and then plant.

If it was planted with saplings and he decided to sow it, he shouldn't say that he will first sow and then uproot; he should first uproot and then sow the seeds. If he wishes, he may cut down the trees to less than a Tefach from the ground, then sow the seeds and only then uproot then trees.

If his field was planted with Kanbus or Luf - he may not wait for them to grow narrow roots, overturn them and then sow, since they only produce such roots after 3 years. (Rather, he must first uproot them and then sow.)

A grain field that sprouted Istis (which damages the grains) or an area of a threshing floor that sprouted many species (that damage the ground) or a fenugreek field that sprouted many species of herb - he is not obligated to weed them. If he weeded or cut some of it down, he is told, "Uproot all of it, aside from one species".

(Gemara) Baraisa: One may put sheaves next to vines (as there's no concern that seeds may fall and grow under the vine).

(R. Yosi): This shows that one may not plant a dry vine next to a dry standing crop.

Question: May one sow next to dried out vines (considering the fact that the entire vine is going to be uprooted)?

Suggested proof: One may not sow next to a dried out vine, but if he did, it does not prohibit - and R. Eliezer said that this is the view of R. Meir, who said that even next to a cotton bush (Tzemer Gefen) it's prohibited to plant (since their leaves are similar to vine leaves) but if it grew there, it is not prohibited. We can learn from here that according to R. Meir, it is prohibited, but since we do not rule like him, it is permitted to sow next to dried out vines.

(The Mishnah taught that if he wishes, he may cut down the trees to less than a Tefach from the ground.) If the vines continued to grow, that which grew until then is permitted; that which will grow after that is prohibited.

It's like the story of R. Shimon ben Yehuda, who cut down his vines to be less than a Tefach from the ground. Afterwards, he told his sharecropper, "Go out and sow (next to the vines)". The vines later grew back and he told his sharecropper, "Go and harvest the crops (that have already grown, before they become prohibited)". After he harvested, the sheaves became wet and began to rot. He told the sharecropper, "Put the sheaves under the vines (to protect them)".

Question (R. Zeira): Perhaps they only permitted that which grew to people like R. Shimon ben Yehuda, who had full intent (when he instructed his sharecropper to harvest the crops); but for others who don't have full intent (and if the sharecropper doesn't do it immediately, the owner won't hurry him to do it), it would be prohibited?

Answer (R. Zeira): Even according to R. Shimon ben Yehuda, it is only prohibited because of Maris HaAyin (that it looks bad, so it is permitted even for other people).