One of the best organic fertilizers out there – at least in terms of how plants respond to it —  is bat guano.  As most of you probably already know, bat guano is made of bat droppings.  What you probably don’t realize is that bat droppings need to be aged for a while in an arid environment before they become guano.  Caves provide the perfect environment for this to occur, and so that is where most bat guano comes from.

Because guano needs to be aged in special surroundings before it is used it is not a rapidly renewable resource.  Instead it’s kind of like peat in that it takes anywhere between decades and thousands of years for the raw material from which it is made to develop into the stuff that we use.  Furthermore, by harvesting bat guano we can actually damage the ecosystems present in the caves from which the bat guano is harvested.  Think about it – bats generally feed outside the cave, so when they defecate inside the cave they are actually bringing new nutrients into the cave – nutrients that other creatures can use.  Whole ecosystems are based on this poo!  So when we harvest bat guano from a cave what we are doing is disturbing a specialized ecosystem – a very unique system.

So am I encouraging you away from bat guano?  No more than I would encourage you to consider reducing your usage of peat – or of oil — or any other non-renewable resource.  I can’t deny that it’s a great fertilizer, but if you want to use an organic fertilizer why not at least consider one that is renewable instead of one that is from a limited resource and which may cause harm to a unique ecological system?

6 thoughts on “Guano”

  1. According to RS Stewart, the Chair – Jamaican Caves Organization, “The wholesale removal of the bat guano [in Jamaica] results in the elimination of not only the bats that made it (through repeated disturbance of a creature that lives on the metabolic edge and is easily driven over that edge), it also results in the elimination of almost every species that lived on it. The cave is effectively sterilized…”
    I haven’t been able to document the same problem in Chilean caves. But some idiot companies are boasting about their bat guano source by putting “Jamaican” in the title of the fertilizer.

  2. How do you feel about so-called “dinosaur-dirt” humate products mined and sold by such at and Not a renewable resource, and the mining must ensure a pretty large carbon footprint for them. But are they worthwhile ignoring the environmental costs?

  3. Real gardeners should utilize their own urine for a nice quick release, environmentally friendly fertilizer.

    Something like 60% of the NPK we excrete comes through our sterile urine. Why flush it where it can end up in our estuaries or at best, go to waste?

    Used with discretion, such as applying before rain or watering it in after application, any odor problems are easily overcome. Otherwise the scent can be a helpful deer repellent.

  4. Bird guano isn’t rapidly renewable — but it isn’t as damaging to ecosystems either. In terms of the dinosaur-dirt, I’m gonna need to do some research on that one!

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