Short Day vs. Long Day Onion Seeds
When planning your vegetable garden there is a lot to consider. Most of us choose what plants to grow based on taste and our needs for the kitchen. Sometimes, however, we need to make these choices based on the needs of the plants as well. Onions are a good example of this. If you look at the vegetable seeds in our seed store you will see that we sell onion seed called long-day and short-day. Why do we categorize them like this, and what does it mean?
Plants and Day-Length
Have you ever wondered why some plants flower in the spring and others in the fall? Remarkable as it may seem, plants can actually tell the time. They know how many hours of daylight there has been, and that controls their growth patterns and decides whether they will produce leaves or flowers.
This ability is normally used to control flowering, but in onions it controls when the onion seeds decide to produce a bulb.
Short-day onions begin to form bulbs as soon as the days reach 10 hours long. This happens by mid-February in Northern States, so short-day onions sown in spring will start to form bulbs almost immediately, before they have grown much. The bulbs you get will be very small, which is not at all what you want.
Long-day onions only form bulbs when the days become 14 or 15 hours long, which happens around the beginning of June in Northern states, but never happens at all in Florida or southern Texas. So if you sow long-day onions in Florida you will never see any bulbs at all. In the north they will have plenty of time to grow before they get the message to start making a bulb.
So if you live north of a line connecting San Francisco and Washington D.C. you should choose from our range of long-day onions in our vegetable seed store.
If you live south of that line, pick something you like from our short-day heirloom onion seeds.
In the north, onions need around 110 days from the date of seeding to mature. So to have bulbs ready by late August you need to sow the seed in your vegetable garden by the early part of May. Onion seedlings are quite hardy, so you can sow as soon as the ground has thawed and begun to warm a little. A later sowing in early June will then give you bulbs in October.
In mild areas in the south you can sow short-day onion seeds in fall and they will be ready by late spring.