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Coffee, Caffeine & Your Plants: Friend or Foe? · Hydroponics Daily

• 0:00
  Hello there and welcome back to
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  Hydroponics Daily, your go-to podcast for everything soilless cultivation.
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  I am your host, Dr. Russell Sharp, and on a previous episode we talked about
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  melatonin, a stress or anti-stress hormone produced in humans,
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  but also in plants and said that it was actually isolated from coffee.
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  People thought that it was a contamination or an artifact and wasn't really
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  in the coffee, but then they found that it was actually produced by plants and
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  was very important as an antioxidant and for controlling the diurnal response to,
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  photoperiod, day length and things like that.
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  But what about the other things in coffee?
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  The other things, caffeine. And what about the effect of caffeine on plants?
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  Well, if you've grown houseplants in an office, you'll know that people often
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  try and put their cold, unwanted coffee and tea, if you're here in the UK,
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  onto plants as a way of getting rid of it so they don't have to go back to the
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  kitchen or wash up and things like that.
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  And the houseplants invariably after a long time, they start to die off. Now why is that?
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  Could it be the caffeine? Caffeine is obviously the major.
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  Stimulant in in coffee
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  and tea and one of the major components and
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  obviously it's people have studied its effect
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  on plants they've put on applications of it and at
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  low doses can have actually have a biostimulant like effect a
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  biostimulant like effect with higher doses inhibitory or outright phytotoxic
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  producing stunted growth and the classic necrosis like the blackening of the
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  tissues that's how they most plants die when you put tea and coffee on them
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  in rooting and tissue contexts milligrams per liter range of caffeine have been brought,
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  been reported to promote rooting but anything
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  above that is harmful so maybe one cup of tea or coffee might be useful but
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  anything repeated is going to cause damage to photosynthesis oxidative stress
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  and things like that a small amount could even induce defense priming or disease resistance,
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  enhanced pathogen resistance, but obviously this is not day-to-day applications.
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  You could potentially apply it as a foliar spray, so throw your cold tea or
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  coffee at the leaves, but most people produce a root drench effectively.
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  So root drenches, you could have germination suppression as well if you've got any seedlings,
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  Thoughts it could be actually a type of allelopathy where plants inhibit the growth of other plants.
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  We've talked about allelopathy in the past, about how some plants inhibit the
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  growth of other plants around them.
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  Black walnut being a classic example, but caffeine has been implicated in allelopathic
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  responses in the past as well.
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  And it could affect the microbes and the fungi in connection with your plants,
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  your lovely mycorrhizae.
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  It can have antimicrobial effects and
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  change the microbial and fungal patterns and communities
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  obviously these will be species specific effects or
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  if you've got things like fungus gnats they could have an effect on pests
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  and disease so it could kill or deter the pests and obviously the one that's
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  been mostly studied is slugs and snails where coffee grounds have been put down
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  around plants to deter slugs and snails people buy get the used grounds from
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  local coffee shops and put them around their plants,
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  but the problem is that you could potentially harm your plants at the same time.
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  So what else? What else could be in the tea and coffee that could have an effect on,
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  on caffeine well sorry on
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  on your plants is they're not the only active compound
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  in the coffee and tea in tea there's
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  a lot of polyphenols or tannins and they
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  can inhibit root enzyme and nutrient uptake they can bind micronutrients and
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  stop them being absorbed or even increase their levels so that's an issue same
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  for organic acids organic acids can do the same and they have the or the added
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  disadvantage is that they can lower the pH,
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  which increases root stress and affects nutrient uptake as well and can precipitate
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  out nutrients so they can't be absorbed by plants.
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  There's a lot of sugar in your tea and coffee. It could stimulate microbial
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  growth, or at the same time, it could have an osmotic stress.
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  It could pull water out of the plants or certainly make it harder for plants
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  to absorb water from the growing medium.
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  So that kind of contribution and if it's very
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  hot then the heat could damage the
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  roots the change in temperature could damage the roots even if
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  it's not direct damage from heat so that's something
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  to consider and then obviously the water will feed the
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  plants and that's why people think that it's useful for plants to have
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  a dose of tea or coffee because they think they're watering the plants when
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  really the the benefits outweigh the benefits are not as high as the disadvantages
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  and the caffeine will accumulate whereas the water will evaporate and so you
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  get this continual caffeine accumulation and it'll take a long time to break down.
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  Also, the other issue is that most houseplants are over-watered.
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  And so if you are watering a houseplant with half a cup of coffee every day
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  in the winter, that's probably too much irrigation for your houseplants.
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  Certainly in an office environment, if multiple people are watering the same
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  houseplant with tea and coffee, then it's probably going to die from over-watering
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  before it gets toxic effects of caffeine.
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  A warm office where people are complaining it's too hot, they're too cold,
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  so they put the heaters on, electric heaters, radiators, and things like that.
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  There's not enough light then that be certainly can kill
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  houseplants okay so that's the effect of caffeine and
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  caffeinated drinks on plants a bit of
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  an interesting one there not directly related to you
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  know commercial production of hydroponic crops but not everything on this podcast
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  is something times it's stuff that's interesting
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  to amateurs and beginners and keen
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  horticulturalists okay hope you found that interesting if
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• 6:08
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• 6:11
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• 6:20
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• 6:29
  thank you very much for listening until tomorrow goodbye.