The melakha of Ĥoresh refers to preparing ground for sowing or planting, by making furrows or holes in the soil in order to plant seeds or seedlings. Plowing also loosens and softens the soil, making it easier for roots to spread out and absorb nutrients.
Thus, one who levels the surface of the ground violates Ĥoresh, because doing so softens the soil and makes it easier to prepare for sowing and planting. Making even a small hole is a transgression of Ĥoresh because a seed can be planted in it. Similarly, clearing rocks from a field, fertilizing it, and weeding are all toladot of Ĥoresh, since these actions improve the soil and make it easier to sow and plant. Anyone who undertakes any activity in order to improve the ground prior to sowing or planting violates Torah law (Shabbat 103a; y. Shabbat 7:2). Even if he does not intend to sow or plant there, he has still violated Ĥoresh, since in fact he has improved the land for sowing or planting (Eglei Tal, Ĥoresh 16).
One may not make a hole in the dirt of a flowerpot or even stake something into the dirt of a flowerpot, thereby making a hole in which one can plant, as these violate the melakha of Ĥoresh (MB 498:91; see n. 4 below).
The Sages prohibited sweeping the ground in the yard, out of concern that one would end up leveling the ground, thus transgressing a Torah prohibition. If it is arable land, he violates Ĥoresh. If it is land that serves simply as a yard, he transgresses Boneh. However, one may sweep a part of the yard that has a hard, paved floor.
One may not kick dirt and sand, or move it around with one’s foot, because this both loosens soil and levels the ground. Saliva that is on the ground should not be rubbed into the dirt with one’s shoes, to avoid leveling the ground. However, if one finds the saliva disgusting, he may step on it in the natural course of his walking, as long as his intention is not to spread it and level the ground (SA 316:11).
One who has mud stuck to his shoes should not try to rub it off against the ground, because he may end up leveling the ground (SA 302:6). Some are not concerned about this possibility, and allow rubbing off the mud (Rema, Taz). One who wishes may be lenient, but le-khatĥila it is preferable to be stringent. In contrast one may rub off the mud against a grate, tiles, or stones even le-khatĥila (MB 302:28; also see above 15:2).