Carrots and radishes form an underground mass during the first summer and the seeds during the second. I use a tiny heated unlit greenhouse. How will they ever know it's 'winter' instead of continuing to grow indefinitely?

  • My first guess would be sunshine hours per day. Plants seem to be more accurate even than a human at measuring those.
  • Temperature (like chestnut seeds do)?
  • Some genetic timer (like humans have the timer "you're already 80, ain't it time to die already")?
  • Humidity?
  • The cold simply murdering off its above ground part (however I've seen Liliums die back solely because the day was shortening)
  • Micro fauna?
  • Magic?

If the answer is something entirely in the control of the farmer - even if we add programmable lightning and air humidity - a 100kg carrot would have hit the news, right?

  • Depends on the plant. For artichokes, those of us in regions too cold for them to survive the winter are advised to plant them inside very early, than set them out in spring to "think" it's winter so they will actually make fruit ( to the extent they do in our conditions) that summer. Alliums go by day length, mostly, as I understand it.
    – Ecnerwal
    Commented Nov 24, 2022 at 2:28
  • Temperature and sunshine hours triggers plants. Last year, the winter got awfully warm before spring and many plants started to flower. And then the winter continued and they died. So temperature is a major ingredient. Greenhouse farmers are growing all sorts of vegetables out of season. So it is under their control. Commented Jan 29, 2023 at 1:56

1 Answer 1


As expected, photoperiod seems to be the major driver with temperature also being important. The actual biochemistry is still being studied. 'several environmental cues, genetic factors and plant nutrition' have also been suggested.

In short, creating a 100kg carrot under controlled environment is probably possible today. The reason we haven't seen it on the news is that no one seems to be motivated enough to invest in such a "useful" endeavor.

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