Many vegetables will bolt when they're grown in the wrong season, and this is because they're photoperiod sensitive. This means that for a short-night plant if the night hours drop below a critical period for particular duration eg. month, they respond by flowering and going to seed. This is undesirable as the leaves stop growing, and become bitter e.g. spinach. They probably do this so that their pollen is available to insects which are active at that time of the year.


So, if you wish to plant a short night plant in full shade for part of the day ( at the beginning or end of the day), does the full shade contribute to the hours of darkness and prevent bolting?

2 Answers 2


That is a good idea, I like where you're going with that...but plant's photo receptors are far too sensitive to be tricked by shade. Even in shade there is still more than enough light for a plant to recognize that it is daytime. If you could instead completely block light out to the plants to make the "night" seem longer, you might succeed in preventing bolting. It probably won't be worth the effort, but it could be a fun experiment.

p.s. I like that you called them short night plants rather than long day plants. Makes way more sense seeing as plants measure the night length and not day length! That has always been confusing to me why we call them short and long day plants. Oh well, cheers!


Being in the shade will not have anything to do with photo period. Darkness has to be complete to count. I have been taught it is more temperature dependent. Too cold after consistent warmth or too warm with a cold spell after warm days and cool nights. I have all my bolting sensitive plants bolting in the spring when the temperatures change drastically one way or the other. No shortening of days in spring yet with one hot day or two I've got major bolting. Same later in the summer with consistent temps and then a cold spell. The plant senses its time is short and ultimately plants need to make seed before they die. Consistency is key to bolting. If you can't control light and temperature and you spike in either two categories your plants will bolt.

  • I don't think that's true as a full moon does not affect the photoperiod. Jan 20, 2017 at 21:03
  • Nope, too low of light but full shade is a lot of light.
    – stormy
    Jan 20, 2017 at 21:05
  • I was objecting to the "Darkness has to be complete to count" sentence. Jan 20, 2017 at 21:14
  • I am sure it isn't 'black and white' but when I am growing cannabis (very photosensitive) when put into bud at 12/12 just a crack of light will disturb the entire show. Seriously. Again, my bolting vegies will bolt early in the spring with aberrant temps. Just one too hot day and forget spinach!! Sighs.
    – stormy
    Jan 20, 2017 at 21:17
  • The other thing is that planting in shade weakens the plant so it inhibits them from going into flower. Jan 20, 2017 at 21:27

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