The melakha of Zore’a refers to causing plants or trees to grow by, for example, planting seeds or saplings or by grafting trees. All actions that improve the growth of branches or fruit are forbidden by Torah law as well. Thus, pruning and weeding are forbidden, because these actions promote plant growth. Similarly, one may not water plants or fertilize the soil surrounding them. It is also forbidden to apply dressings (such as tar or paint) to a tree’s wounds in order to heal it (Shabbat 73b; MT 7:3, 8:2).
One may not leave an avocado pit in a dish of water so that it will take root and begin to grow. Likewise, one may not put a branch in water so that it will take root and start growing.
Included in the prohibition is germinating seeds in water so that the sprouts can then either be eaten or transferred to soil. It is also forbidden to soak seeds in water to soften them, preparing them to take root and grow (SA 336:11). However, one may soak barley to soften it before feeding it to animals. This is because one does not desire for the barley to grow; besides, the barley is removed from the water and fed to the animals before the roots emerge (MB 336:51).
One should not toss seeds onto damp ground. Since they could start growing, one who tossed them would be guilty of planting on Shabbat. However, one may throw seeds somewhere they probably will not grow. Therefore, one may throw seeds in a place where people walk regularly, or in front of animals who will eat them within a day or two (SA 336:4).
One may not open or close the windows or doors of a greenhouse in order to encourage the growth of the plants inside. However, if there is a houseplant in the room, one may still open the shades and the windows for one’s own sake, even though the sunlight and air that enter will indirectly help the potted plant grow. Since he did not open the shades and windows for this purpose, and the benefit to the plant is remote, it is not prohibited (as it is a psik reisha in a case of a double rabbinic prohibition, since the melakha is done both with a shinui and via grama; Har Tzvi, OĤ §133 and Yeĥaveh Da’at 5:29).
. If one plants a seed on Shabbat but removes the seed from the ground before it takes root, then according to Rashash, he has not violated Torah law, because the prohibition takes place only when the seed takes root. According to Minĥat Ĥinukh and Eglei Tal, Zore’a 8, simply placing the seeds is already a Torah prohibition.. According to Nishmat Adam 11:1 and AHS 336:30, planting seeds even in a planter that does not have holes is prohibited by Torah law. In contrast, according to Mahari Ĥagiz and Eglei Tal, Zore’a 9, the prohibition is rabbinic, since normally people do not plant using such a flowerpot. The reason that soaking seeds is prohibited by Torah law is because that is the way it is generally done (see Menuĥat Ahava vol. 2 ch. 3 n. 33). Recently, people have begun growing seeds and plants hydroponically, using water and a combination of chemicals to substitute for the nutrients normally found in soil. It would seem that all would agree that one who plants seeds hydroponically violates Torah law, since nowadays this is a normal way of planting, similar to the case of planting in dirt on a roof (Responsa Rosh 2:4).