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I want to grow large cacti, see my previous question. So I start with small plants and to keep them growing in winter time I want to give them LED (special grow) light.

I was wondering about the best light periods for the small young plants. I am interested in finding the best daily light period (how many hours per day?), and as well on when to start giving them artificial light (which months?). I was thinking of starting to put them under a light from November till February? Does that seem right?

I live in the Netherlands (latitude 52). I hope anyone can share his/her experience with indoor light regimes?

  • Simple, mimic their natural habitat; that's all there is to it. – Rob Aug 24 '18 at 16:46
  • I'm a little unsure of your situation. Do you not have sufficient sunlight in the winter to support the seedlings? Are you going to supplement sunlight with LEDs or will they be the only light source? – Tim Nevins Aug 24 '18 at 19:06
  • Day length by latitude: orchidculture.com/COD/daylength.html Where do your cacti live naturally? – Wayfaring Stranger Aug 28 '18 at 20:04
  • Useful link @WayfaringStranger, thanks. The cacti (seedlings) are from North-West Mexico/Arizona. Around latitude 30 N I think. – benn Aug 28 '18 at 21:16
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Regardless of light I think keeping the soil warm with a seedling mat or something would help keep the seedlings growing during the winter.

My experience growing cactus seedlings under lights was with fluorescent grow lights. I had them within 5 cm of the plants and it still wasn't enough. I had an LED for a while but it died before I could determine its effectiveness.

I asked a couple of questions in the comments about the light situation. My personal opinion at this point is only the proven grow lamps like MH or HPS are effective. I'm still not convinced LEDs have the power for robust growth, but technology marches on, so my experimentation a few years ago may be irrelevant.

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  • Thanks for sharing your experience, Tim. In winter there is not enough sunlight here, so the LED will be the only light. I bought the light on eBay, it the 10W with 25 reds and 11 blues. First LED I bought so it is new for me as well. I can't put my plants in a colder room (~10C/50F) for dormancy, because my apartment is always between 16-25C (60.8-77F). Is that enough for cacti? – benn Aug 24 '18 at 20:04
  • It should be, but a small heat mat for the plants to rest on will keep their roots warm. If you are going to put just seedlings I'd say 12 on and 12 off for the light. If you are going to use this for everything maybe 8 on 12 off or whatever your normal day length is during winter. The seedlings won't care as long as it's not on 24 hrs a day, but it might goof up flowering on a mature plants. Don't put the heat pad under any mature plants, just seedlings. Start out with the light 10 cm or so from the plants if possible. The difference between lights and the sun is HUGE! – Tim Nevins Aug 24 '18 at 21:36
  • This is great advice ("seedlings won't care as long..."), so I can indeed try to follow the day lengths here in winter (around 8h is min. here). It is mostly meant for the seedlings, but I might try to fit some small ones under the light as well. – benn Aug 25 '18 at 6:51
  • 10C/50F is perfectly OK for a dormant cactus. The way to make them go dormant is zero watering. I have cacti that live on the house windowsills, with only 8 hours natural daylight in winter, and the windowsill temperature behind the curtains at night is lower than the rest of the room. They get no watering at all from about the end of September to the first spell of "sunny weather" in March or April. They thrive, and flower annually - but I'm not interested in growing big plants quickly as an end in itself. – alephzero Aug 27 '18 at 20:37
  • Thanks @alephzero, but my question is not about how to get cacti in dormancy. I know that cacti will survive winters, but that was not the question. – benn Aug 27 '18 at 21:08
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Most cacti are happy to have "growing season" in summer and a "resting season" in winter. After all, in their natural environment water is unlikely to be available all year round for continuous growth. When they are dormant in the "rest" period, light levels and high temperatures are not so important - though clearly you need to keep the temperature above freezing. Even temperatures that dip below freezing won't necessarily cause any damage provided you don't have daily freeze-and-thaw cycles, which are guaranteed to damage them.

Many cacti can deal with quite high volumes of watering in summer and grow fast as a result, so if your objective is "quick growth" giving them a rest for 4 to 6 months each year might not be as bad as you imagine.

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  • I know, but in my apartment I have not a cool room. So there will always be a temperature of 16-25 C. So no place for proper dormant, that will need lower temperatures of around 10C. Point is, with high temperatures and low light you can get elongation which is not very pretty. – benn Aug 27 '18 at 21:04

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