I recently read that foliar feeding should be avoided when the lights are on. Is this true? Does this mean foliar feeding is not an option if I run my lights 24/7? Would it be worth it to turn the lights off for a short period of time to foliar spray, then resume my 24/7 schedule?
First of all, I would like to thank you for such a great question relating to the article: The Do's and Don'ts of Foliar Feeding.
I want to kick this off by reminding readers that we are specifically talking about foliar feeding in an indoor gardening environment, under high intensity discharge lamps.
To answer the first part of your question, yes, foliar feeding should be avoided when the lights are on. Due to the powerful heat given off by the lights, the foliar spray feed can dry out and evaporate before it has a chance to be absorbed by the leaves.
Even worse, it can cause the spray to become baked on to the surface of the leaf which can then have detrimental effects on the leaves ability to photosynthesize, as the baked-on layer of foliar spray will block the plant’s stomata and prevent CO2 and oxygen from entering and leaving the plant.
Another possible scenario is that if the lights are hot enough, the foliar spray can act like a lens (think magnifying glass) and can cause the surface of the leaf to burn, thus destroying your plants.
To turn your lights off for a few hours (three to four hours is more than sufficient) in order to use a foliar feed would definitely be of massive benefit to your plants, just make sure that you apply the feed as close to lights-off as possible.
My opinion has always been that your lights do not need to be on 24/7 at any point of the growing process as I find that it is good for plants to have a rest period (few plants in nature are exposed to a 24-light cycle).
This is how I have always operated my growroom and I have never found that my results are in any way inferior to those of friends and colleagues who choose to go 24/7 with their lights.
Lights off means you get the added bonus of being able to foliar feed and give your plants that extra “push.” So yes, to answer your final question and sum up… I definitely think that it is worth turning your lights off in order to take advantage of the wonderful benefits of foliar feeding and maybe reduce energy costs at the same time.
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