When the shallot seedling emerges from the soil it only makes foliage at first. The bulb, the shallot itself, still has to be formed. Allium crops, such as shallots and onions, require a specific number of hours of daylight to create a bulb. Garlic is less sensitive, but shallots and onions are very sensitive to the day length.

Day length, as the words suggest, is the number of hours of daylight during the day. This differs depending on the latitude of a region. To give an example, in the Netherlands there are almost 17 daylight hours on the longest day of the year, while in Spain there are about 15 hours. This is the other way round during winter. Each variety of shallot has its own specific daylight need; some varieties need a “long day”, while others favour a “short day”. The number of daylight hours in a particular region influence which varieties can be grown there. A shallot will simply not form a bulb if the days are too short for its needs.

As well as the all-essential daylight, the temperature and type of light also dictate whether a plant forms a perfect bulb.