What do clothes, animals and plants have in common? They are all subject to a prohibition the Torah calls kilayim.

So what is this prohibition all about? The Torah forbidsWhat do clothes, animals and plants have in common? combining certain species of animals and plants in specific ways. This prohibition includes some intricate details, as well as some fascinating lessons. Let’s begin from the beginning.

In the book of Leviticus:

You shall observe My statutes: You shall not crossbreed your livestock with different species. You shall not sow your field with a mixture of seeds, and a garment which has a mixture of shaatnez [the combination of wool and linen] shall not come upon you.1

Then later, in the book of Deuteronomy:

You shall not sow your vineyard [together with] a mixed variety of species, lest the increase will forbid the seed that you sow and the yield of the vineyard.2 You shall not plow with an ox and a donkey together. You shall not wear a mixture of wool and linen together.3

All told, the Torah lists the following general prohibitions:

  • Not to crossbreed animals
  • Not to plant various plant species together
  • Not to wear a garment with shaatnez
  • Not to use two species of animals to plow together

In the Talmud4 there is an elaborate analysis of these verses, as well as descriptions of the details of these prohibitions. There are actually 77 mishnahs devoted to the topic. In MaimonidesYad Hachazakah there are no less than 181 paragraphs devoted to the prohibition of kilayim!

Leaving out most of the discussion about these laws, this article will focus on:

  • the word kilayim.
  • some of the basic laws of kilayim.
  • possible reasons for this law, and lessons we can learn from it.

The Word

Kilayim (כלאים) is a rare word, appearing in the Torah only in context of these prohibitions. So how does this word come to mean “mixture”?

The root word K-L-A (כלא) is used elsewhere in scripture to denote “being held back,” or “arrested.” At times, it has a (related) meaning: to “cease” or “expire.” 5

Accordingly, Zohar,6 among other texts, explains kilayim to mean “entrapments,” since two species are being forced to be together.

As we shall discuss, the meanings of this word may shed light on the significance of these laws.

Some Laws of Kilayim

The prohibition of kilayim can be divided into six basic categories:7

1. Not to plant mixtures of seeds. If one finds a plant growing from a mixture of seeds in one’s field, one must uproot it.

There needs to be a recognizable distance between the various species growing in one’s field so that they are not considered “mixed.” The distance required varies with the particular circumstances, and is discussed in great detail in the Talmud and commentaries.

Whatever has grown from seeds that grew in proximity to each other may be eaten and also replanted.

There is debate as to whether a Jew can hire a gentile to plant kilayim.

This prohibition (with the exception of grapes) applies only in the Land of Israel.

See Maimonides, Laws of Kilayim, Chapters 1-4

2. Not to graft trees of different species together. It is permissible to mix seeds from different kinds of fruit trees, or to mix seeds of fruit trees with other kinds of seeds,8 or to have them growing in close proximity to each other. The prohibition of kilayim for trees is specifically about grafting different species together.

In this case, too, it is permissible to eat and replant the produce of a grafted tree.

A Jew may not hire a gentile to graft trees. According to some opinions,9 a gentile may not graft trees, even if it is not for a Jew.

This prohibition applies in all places, not only the Land of Israel.

See Maimonides, Laws of Kilayim, Chapter 5

3. Not to plant grape seeds with other kinds of seeds. For example, one may not plant seeds of wheat, barley and grapes together. This prohibition applies specifically to planting two species of seeds in addition to the grape seed.10

In addition to not being planted together, grape vines growing alongside other plants should have a divider between them, or should be grown at least a distance of four cubits apart so that they are considered not to have grown together.11

It is forbidden to derive benefit from grapes and otherThere needs to be recognizable distance species that grew in proximity to each other without a divider or a distance of four cubits.

The amount of time it takes for the vines and the plants growing near it to become forbidden, as well as how much of each plant becomes forbidden, varies according to the circumstances, and is discussed at length in Jewish law.

While the Torah prohibits this category (of vineyard kilayim) only within the Land of Israel, the sages have required us to observe it in all places.

See Maimonides, Laws of Kilayim, Chapters 5-8

4. Not to crossbreed animals.

It is permitted to benefit from crossbreed. It is also permitted to breed two crossbred animals, if both of their mothers were of the same species.

A Jew may not hire a gentile to crossbreed animals on his or her behalf.

This prohibition and the next two prohibitions apply in all places.

See Maimonides, Laws of Kilayim, Chapter 9

5. Not to harness two animals from different species together to work, if one is “pure” (a kosher animal) and the other “impure” (not kosher).

The definition of “work” includes activities such as plowing, planting, pulling a wagon, etc.

While the Torah prohibits this kind of work only when one of the animals is kosher and the other one is not, the sages have expanded the prohibition to include any two animals that are not of the same species.

See Maimonides, Laws of Kilayim, Chapter 9

6. Not to wear a garment made of wool and linen. This is also referred to as shaatnez.12

This prohibition is referring to when the wool and linen are in some way connected to each other, e.g., they are sewn or tied together. But wearing two different garments, one of wool and the other of linen, is permitted.

As opposed to many other laws (including some of the laws of kilayim), there is no measurement to this prohibition. Even one thread of linen in a garment of wool is prohibited.

It is permitted to manufacture and sell garments that contain shaatnez, as the prohibition is specifically about wearing shaatnez.

If one realizes that one is wearing shaatnez, the garment must be removed immediately.

See Maimonides, Laws of Kilayim, Chapter 10, and here for more on the laws of shaatnez.

Reasons and Significance

The prohibition of kilayim is first introduced in the Torah with the words, “You shall observe my statutes.” The word for “statutes” in the original Hebrew is chukim (חקים), which usually refers to those laws which have no known reason.

In the Talmud13 there is a list of commandments that are considered “statutes,” and one of them is לבישת שעטנז, literally, “the wearing of the mixture of wool and linen.”

Rashi14 understands this passage as referring to all the categories of kilayim, meaning that there is no explanation for them.

There are other classic commentaries that are of the opinion that the Talmud is referring only to the category of wearing shaatnez, but that the other categories can be understood. This is the way Nachmanides15 explains the meaning behind kilayim:16

G‑d instilled in the various species the ability to reproduce so that that species will continue to exist for as long as He wishes. When one crossbreeds (whether animals or plants), it is as if the person is indicating that G‑d didn’t create all necessary beings, and this person wants to assist in the creation of the world.

Additionally, crossbreeding means that the species that was meant to be continued through the power of reproduction is now being (somewhat) discontinued, and instead producing a different species.17

Why No Plowing?

In regards to the prohibition of harnessing two animals together, some of the classic commentators explain that the prohibition prevents pain or discomfort to the animals. It would be uncomfortable for a donkey to constantly hear the ox chew its cud.18 Or, alternatively, the ox will plough quicker than the donkey, and their speed will not be coordinated.19

The difficulty with this explanation is that it doesn’t explain why all species of animals are not allowed to be harnessed together.It would be uncomfortable for the donkey to constantly hear the ox chew its cud The prohibition should apply only to those species that cause discomfort to one another.20

Nachmanides21 posits that this prohibition serves as a safeguard, so that the owner will not come to crossbreed the different species.

Torah Going Green?

I’ve often wondered what the Torah might have to say about the level of concern we need to have about protecting the environment, and if it should be our concern if a particular animal will become extinct or not.

Even the prohibition of baal tashchit (not to destroy things that can be useful) seems, at least at first glance, to be more about preserving that which could be useful to humankind, rather than about caring about the item or animal that is being preserved.22

In the second reason Nachmanides gave, there seems to be a concern about the very idea that a species that G‑d created should be prevented from continuing.

In truth, however, there probably isn’t much to infer here in regards to any action one should take for preserving the various species of the environment. Since the Nachmanides (in the context of this verse) is talking only about not actively destroying or discontinuing a species, not about going out of one’s way to preserve it. But at least we can infer that the Torah values the preservation of nature.23

Innovation vs. Conservation

In Nachmanides’ first reason for the prohibition of kilayim, he seems almost to condemn the whole idea of being creative and innovative! He says that coming up with something new is considered an affront to the Creator. However, it would seem that Nachmanides is not trying to negate being innovative, rather he is saying that there is a difference between working and creating within the framework that G‑d gave us, and then remaking the framework itself.24

Humanity has a strong drive to change, create and innovate— break free of all boundaries. Simultaneously, there is a desire for safety, for familiarity and to be led by a trusted higher being Who guides our behavior.

Perhaps we could hear in the words of Nachmanides the idea that G‑d wants us to not only utilize both of these inclinations but to blend them. We need to truly grow, innovate and create to reach the potential that G‑d gave us. But there are boundaries to our creativity. We invent and create, but only within the context of an awareness of the true Creator, His ultimate power and His laws.

The boundaries of our creativity are the natural boundaries that G‑d created—the distinct divisions between the various species. Additionally, we are mandated to direct our creative explorations only in ways that don't transgress the spiritual boundaries—namely, the laws of the Torah,There are boundaries to our creativity which are as iron-clad and embedded in reality as the laws of physical nature. Transgressing them will not lead to a truly creative and productive result. As the verse says, “If not for my covenant [being kept] day and night, I would have not established the laws of heaven and earth.”25