Overwintering

Day length explains bulbing, right? But it does not fully explain bolting.

And bolting is the reason that overwintering onions is a little bit of a different proposition than spring planting.

So for that, we need a second mechanism, and that is vernalization.

Hey, what do you mean you heard that word before? Yes, we heard that word last week when we were talking about garlic, right? Remember, vernalization is a period of cold that is needed for a plant to take a specific action.

If the plant is too large going into that cold, meaning it has already built up enough size that it reads as a mature plant rather than a juvenile one, it is far more likely to respond to vernalization by bolting.

And when I say bolting, what I mean is sending up that hard woody flower stalk instead of continuing to build that bulb.

This is why overwintering onions have to go into the winter fairly small, okay? So if you're planting from transplants, we're talking about the width of a pencil.

If you're talking sets, we really only want them about a quarter of an inch across.