HOW DO WE KNOW THAT IF A SEED-BED IS SIX HANDBREADTHS SQUARE, WE MAY SOW THEREIN FIVE KINDS OF SEEDS, FOUR ON THE FOUR SIDES, AND ONE IN THE MIDDLE?
Imagine a square only six handbreaths long on each side with a row of plantings on each length, but not reaching the corners (so there is no mixing) and not reaching the middle. Each side of the square has a different species planted on its length and a fifth one planted in the middle. Again, making sure no species touches another.
How do we know that this kind of arrangement (or something like it) is permissible?
BECAUSE IT IS SAID, “FOR AS THE EARTH BRINGETH FORTH HER BUD, AND AS THE GARDEN CAUSETH ITS SEEDS TO SPRING FORTH” (Isa. 61:11) NOT “ITS SEED”, BUT “ITS SEEDS” IS STATED.
This “proof text” while not specific in its image, implies that there must be a way to sow multiple kinds of plants in one “garden.” The rabbis then try to figure out how.
The prohibition is clear. But a solution can be found. That's rabbinic imagination.