Halakhah sa Levitico 19:19: Mishneh Torah, Diverse Species, Mishneh Torah, Human Dispositions, Mishneh Torah, Rest & Kitzur Shulchan Arukh

1. A person who sows two different seeds as one in the Land of Israel receives lashes, as it says "You shall not seed kilayim in your field" (Lev. 19:19)

5. The mixing of trees fall under what is written "You shall not sow in your field mixed seeds" (Lev. 19:19). For example, the one who grafts a tree on another tree, for instance, an apple on an etrog or an etrog on an apple, behold this one receives "Torah lashes" [for transgressing a Torah law] in any place, whether in the land or outside of the land. And the same applies to one who grafts a vegetable on a tree, or a tree on a vegetable, this one is lashed in any place.

One who controls himself with increased restrictions, and distances himself even from the mean tendency,²Shabbat, 30-31. G. a little one way or a little the other way, is called devout. How may one do it? One who will distance himself from the extreme point of arrogance and become exceedingly humble is called devout for, this is the tendency of piety. If one distances himself to the mean point only and practices meekness he is called a wise man for, this is the tendency of wisdom. A like pathway exists in all the rest of the tendencies. The ancient devotees diverged their tendencies from the middle-path facing the two extremes; some tendency they bent opposite to the last extreme and some tendency they bent opposite the first extreme. This is more than being within the limits of the law.³Baba Mezi’a 30a. G. As for us, we are charged to walk in these middle-paths, which are the good and straight paths, even as it is said: "And thou shalt walk in His ways" (Deut. 28 9).