My cabbage....didn't.

[TheGrey]

A cabbage seed that I planted last year in the garden box decided to grow this year. I had no time to garden this year, so when I saw it sprout I was surprised, but left it alone to do its thing.

Which is what it did, I guess.

Please excuse the horrible photos, but I'm hoping that someone will be able to tell me why the cabbage grew like this, and what I can do to prevent it next year. I've never seen such a goofy-looking cabbage plant before.