What is the definition of "mingled seed" in the command, "thou shalt not sow thy field with mingled seed," found in Leviticus 19:19, and Deuteronomy 22:9? Notice the reason for this command in Deuteronomy 22:7, "...lest the fruit of thy seed which thou hast sown, and the fruit of thy vineyard, BE DEFILED." God gave this law for our protection! He does not want us to defile or mix the produce that we grow, nor the seed that we Save for growing future crops.
Just to make sure the point is clear, let us state a few specific examples. You should not plant cucumbers near watermelons because they will cross and produce a perversion. Likewise, the various members of the muskmelon and cantaloupe family will mix with pumpkins and certain types of squash. They should not be planted near one another. But there is nothing wrong with planting peas or beans among your corn, or planting two pasture grasses together. In neither of these cases would one crop "defile" or mix with the other in any way.
In the beginning God caused each plant and animal to reproduce after its own kind (Gen. 1:11, 21, 24). God twice commands us to follow that example instead of mingling our crops (Lev. 19:19 and Deut. 22:9). We should plant those seeds that will reproduce after their own kind.
Hybrids that produce confusion and an inferior quality after the first year should NOT be used. "... God is not the author of confusion..." (I Cor. 14:33). Many scriptures show us that God wants His people to produce and own quality products.
We should use good quality seed that will produce a consistent good quality year after year. Good seed planted in land that is properly worked will produce strong, healthy plants that bear profitable crops.
Many of our seeds have come down from crosses, but have had the inferiorities selectively bred out, so that we would not know whether a particular strain of produce has come from a mixed, or a pure, past. In such cases, it is permissible to use seed that may have come from a cross in past years, if the inferiority has been eliminated by wise selection of seed, so that the seed produces a pure crop of its own kind.