From online, while I was looking into cutting some leaves to make the bulbs grow bigger. I thought it was very interesting, so copying it here.
"There are two growing periods in the life of an onion. The first growing period is the growth of the leaves. Each leaf eventually produces an onion ring, or layer; the larger the leaf, the larger the ring will be. The perfect onion has 13 rings, so the goal is to create 13 leaves before the onion starts the second stage of its growing cycle by transferring the carbohydrates that are in the leaves to the rings of the onion (bulbing). Once the bulbing process begins, no more leaves are created. Because the key to producing a large onion bulb is to grow healthy and large foliage, there are critical steps that need to be followed to achieve numerous, healthy, and large leaves."
Now, who figured out that "the perfect onion has 13 rings"?
Certainly not someone with triskaidekaphobia, or fear of the number 13!
"There are two growing periods in the life of an onion. The first growing period is the growth of the leaves. Each leaf eventually produces an onion ring, or layer; the larger the leaf, the larger the ring will be. The perfect onion has 13 rings, so the goal is to create 13 leaves before the onion starts the second stage of its growing cycle by transferring the carbohydrates that are in the leaves to the rings of the onion (bulbing). Once the bulbing process begins, no more leaves are created. Because the key to producing a large onion bulb is to grow healthy and large foliage, there are critical steps that need to be followed to achieve numerous, healthy, and large leaves."
Now, who figured out that "the perfect onion has 13 rings"?

Certainly not someone with triskaidekaphobia, or fear of the number 13!