Some soils seem to produce sweeter onions than others. Soils high in sulfur seem to produce more pungent onions. Onions come in the colors white, yellow or red. The shape is globe or round, flattened or torpedo shaped. An interesting aspect of onions is the effect of day length on plant growth.
Many plants are sensitive to the hours of daylight and darkness they receive.
When onions are first planted, their growth is concentrated on root and top formation. Once a specific combination of daylight and darkness is reached, bulb formation begins. The tricky part is that each variety needs a particular combination. A short day onion is responsive to 11 or 12 hours of daylight, an intermediate day onion needs 12 to 14 hours of daylight, a long day onion requires 14 or more hours of light. For those of us in the northern part of the U.S., we need to select long day varieties.