"In the seventh book I will include commandments that apply to crops, such as the sabbatical year and Jubilee, tithes and priestly offerings, and other commandments that are included with them involving similar matters. And I have called this book the Book of Crops."

34. Mixtures - Kilayim

It is forbidden to plant two types of crops (that are used for human food) together or to graft one type of plant on another, as it says "You shall not plant your field with a mixture".¹ The prohibition of planting applies only in the land of Israel. Different types of crops must be separated far enough that they either appear separate or do not draw nourishment from one another.^a

It is forbidden to plant any crop (other than a tree) near a vine, and there is a special prohibition against planting a mixture of two crops near a vine, as it says "You shall not plant your vineyard with a mixture"²; this latter prohibition applies rabbinically even outside the land of Israel. If one does so it is forbidden to derive benefit from them, as it says "Lest the increase of the seed that you have planted and the crop of the vineyard become holy".^2,b

b) Mixtures of Animals

It is forbidden to cross-breed two types of animals, as it says "You shall not breed your animal as a mixture".¹ It is forbidden to do work with two types of animals together, as it says "You shall not plow with an ox and an ass together"³; but unless they are land animals, one of them permissible to eat and the other forbidden, this prohibition is only rabbinical. Breeding or working with a sacred animal that has become unfit is also forbidden since it is like a mixture of sacred and profane.^c

c) Mixtures in Clothing

It is forbidden to wear a mixture of wool and linen, as it says "You shall not wear a mixture of wool and linen together",⁴ and it says "And a garment made of a mixture shall not go upon you".^1,d

Sources:
1. Lev. 19:19	a. 1:1,4-5; 4:16
2. Deut. 22:9	b. 5:1,3-6,7; 8:13-14
3. Deut. 22:10	c. 9:1,7-8,10-11
4. Deut. 22:11	d. 10:1