I have Vaccinium membranaceum (black huckleberry) seedlings growing in a greenhouse. I have the option of providing fluorescent light to the plants 24 hours a day.

However, it has occurred to me that plants like Vaccinium membranaceum might require a minimum amount of darkness per 24 hours.

What darkness requirements do Vaccinium membranaceum plants have?

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  • $\begingroup$ This is likely to vary greatly given that some Vaccinium species grow under thick (shaded) canopies while others are capable of growing in clearings and forest gaps. So, they would experience different amounts of light to begin with. Are you instead thinking that perhaps temperature differentials or time spent respiring might impact the plants? What research have you tried to do on this topic on yoru own? $\endgroup$ Feb 10, 2018 at 17:27

2 Answers 2


Some plants are long day plants -- they require a certain number of days longer than a certain number of hours.

Some plants are long night plants -- they need nights that are longer than a certain number of hours.

See this for more details: http://www.biology-pages.info/P/Photoperiodism.html

Other plants are day neutral. They bloom when triggered by other stimuli such as it being warm enough.

If you don't care if they bloom or not, then you can give them 24 hour light. They should grow somewhat faster.

However, you may need to check what triggers them into dormancy. E.g. Spruce start going into dormancy when days get shorter than about 10 hours (Varies by species, and provenance) Reforestation growers trick them into going dormant in August with black tarps in mid afternoon. They can then plant them with minimal stress, and they take off in the spring.

  • $\begingroup$ Please add citations or additional support to backup some of your claims. Thanks. $\endgroup$ Feb 10, 2018 at 17:23
  • $\begingroup$ Can't. First year botany lecture 45 years ago. $\endgroup$ Feb 11, 2018 at 2:13

My old plant physiology textbook is at the office and it has been 15 years since I had the class so going a bit off memory here... But yes, they do have a circadian rhythm and benefit from having a dark cycle. There really isn't any need or extra benefit from having them under more than 16 hours of light. I can dig out specifics from my textbook and old class notes later if someone else doesn't chime in with more info...

  • $\begingroup$ Recalling info from memory is much better reserved for a comment on this site. Answers should be complete. I recommend that you find your textbook and provide direct evidence (either a quote, citation, etc.) to support your claims. Thanks. $\endgroup$ Feb 10, 2018 at 17:25
  • $\begingroup$ What's the title of the textbook? I'll order a copy. $\endgroup$
    – User1974
    Jun 27, 2019 at 16:34

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