When And How To Use Bat Guano For Weed

This might seem like an obscure topic of conversation, but you may be surprised to learn that bat guano has long been sought after as a means of boosting the performance of cannabis plants. But how does guano work as an organic fertiliser, and when should it be used? We'll answer these questions and more!

What Is Bat Guano?

Bat guano is essentially droppings. As bats live in large colonies in the same cave for many generations, the floors of said caves get completely covered in excrement over many years. It is then accumulated to become compost.

Otherwise known as “wanu” by South American Quechans, guano is a nutrient-rich superfood that can be used as a fertiliser for weed plants. In addition to bats, various seabirds produce guano.

Bat Guano Has a Rich History

The use of bat guano is nothing new; in fact, documented use of guano stretches back more than 1,500 years. Guano has even been responsible for conflicts between countries because of its value and desirability. Not only used as plant nutrition, guano was also utilised as an ingredient to produce gunpowder and explosives.

Before the arrival of Europeans, guano was used as a fertiliser by the Incas and other South American cultures. To control how much could be harvested, Incan rulers distributed the guano-bearing islands among the leaders of various provinces. These provinces were then strictly monitored and regulated.

Although ultimately guano is animal waste, its value cannot be understated. Absolutely huge fortunes have been made and lost since the discovery of guano's applications. As one of the world's biggest harvesters of guano, Peru exported well over 20 million tonnes over a period of 40 years, making a profit of around 2 billion dollars.

Why Is Bat Guano Good for Cannabis Plants?

As bat guano is simply teeming with nutrients, it can support cannabis plants through both the vegetative and flowering stages. And because it’s an organic fertiliser, when applied correctly, it should only enhance the substrate and help to keep the microbial life thriving. It also promotes a better soil texture and aids in healthy decomposition of organic material in the soil.

With this in mind, any weed grower looking to lighten up or eradicate their synthetic fertiliser use should consider guano as a one-stop-shop for healthy, thriving plants.

What Macro and Micronutrients Does Bat Guano Contain?

Bat guano contains the three essential macronutrients needed for healthy plant development: nitrogen, phosphorus, and potassium.

Nitrogen supports the cannabis plant during its vegetative cycle, while phosphorus supports the roots and ensures healthy flowering. Lastly, the right levels of potassium will more or less guarantee sturdy and robust branches and stems.

Fortunately, guano is simply teeming with these nutrients, as well as an abundance of micronutrients set on giving plants the best quality of life possible, including:

• Boron — Helps plants utilise calcium; contributes to protein formulation
• Calcium — Essential for cell wall growth in root system; improves nutrient uptake
• Iron — Contributes to leaf respiration; influences enzyme production
• Magnesium — Regulates enzyme production; plays key role in converting light into energy
• Manganese — Necessary for creating chlorophyll; key to photosynthesis
• Sulphur — Enhances plant metabolism; promotes root growth
• Zinc — Used in protein building; regulates enzyme function

Those with a keen eye will notice that these micronutrients are also found in everyday store-bought fertilisers. However, as guano is naturally sourced, there is no risk of additional chemicals or additives diluting the effectiveness of the nutrients on offer.

Are There Any Risks to Using Bat Guano?

While there are plenty of factors to love about bat guano, it's not without its downsides. Sourcing guano can be an expensive and difficult endeavour. Or, more specifically, finding bat guano products that are suitable to use at home on your marijuana plants can be a tricky task.

Not only that; if guano is harvested incorrectly, it can be devastating to its respective ecosystem. Unfortunately, the sheer demand for guano to this day has led to some unethical harvesting methods. These, in turn, have had some catastrophic effects, disrupting the bat population and impacting biodiversity within the caves.

There are also health hazards associated with mining guano, with many workers susceptible to contracting histoplasmosis—a type of infection caused by breathing in Histoplasma, a fungus prominent in areas with large quantities of bat guano. So it's best to leave the guano mining to ethical companies that operate in sustainable areas.

When and How To Use Bat Guano for Marijuana

If you're fortunate enough to get your hands on some commercially available bat guano, it's easy to utilise in your home growing projects. With that in mind, we've put together a few methods you can try to get the best performance out of your plants.

Guano Super Soil Mix

The soil your cannabis is grown in has a huge impact on its development and final yield. As bat guano has basically all the macro and micronutrients required for cannabis plants, it's ideal to use as an ingredient in a super soil mix. This will give your plants a steady stream of nutrients throughout their growing cycle.

However, it is unsuitable for the germination of seeds, young seedlings, or clones, as they are too delicate at this stage. To make your cannabis super soil mix, you will need:

• 4 parts starter soil
• 1 part worm castings (or coffee grounds, sand, or compost)
• 1 part coco noir
• 1 part perlite/vermiculite (to allow for additional drainage)
• 2.5–5% guano
• 2.5% bone and/or blood meal

Combine these ingredients in a container, and you'll have a nutrient-rich mix that will serve your plants extremely well for the duration of their growth. Simply transplant your cannabis into the soil and continue regular maintenance and upkeep, and you'll surely be rewarded with healthy, bountiful buds.

Watering in Bat Guano

If you're looking to give your weed plants a nutrient boost now and again, you can add a little guano to your watering routine. Simply add 2 to 3 teaspoons of guano to a gallon (~3.79 litres) of water, then administer to your plant.

Cold Water Extract

One variation on this theme is to provide your plants with cold water guano extracts. This is similar to watering in as usual, but by allowing the guano to sit in the water for several hours before administering to your plants, it allows for a better extraction—really feeding your plants as opposed to giving them a light boost. This is a method to use sparingly, but you'll be surprised just how well your plants react to it.

Aerated Guano Tea

Building on the idea of creating guano extracts at home, it's entirely possible to make an aerated tea. You can effortlessly extract the macro and micronutrients by stirring in 1 tablespoon of guano per litre of warm water. Leave the concoction overnight, and in the morning you'll be met with a nutrient-rich tea that you can use once per week to promote plant growth and overall soil quality.

Adding Bat Guano After Potting

If you've started your growing project before getting your hands on some guano, don't worry! You can look to add some after potting, and it's straightforward to do. Don't sprinkle the guano onto the topsoil; dig under the soil surrounding the plant and place it there. This will allow it to activate properly. Make sure to provide some water so it's mixed in well with the surrounding soil.

Can Bat Guano Burn Cannabis Plants?

Because of the nutrient-rich nature of bat guano, using too much, or using it too early, can cause nutrient burn. This is why it should be used sparingly, and only after your plants have passed their seedling phase.

You'll almost certainly want to go with a reputable brand when it comes to purchasing guano. However, while Zamnesia's Headshop doesn't sell guano per se, it does have plenty of organic fertilisers and boosters that provide all of the macro and micronutrients that guano is known for. So if you're struggling to get your hands on the real thing, we've got plenty of options to rival the guano experience.

Adam Parsons

Professional cannabis journalist, copywriter, and author Adam Parsons is a long-time staff member of Zamnesia. Tasked with covering a wide range of topics from CBD to psychedelics and everything in between, Adam creates blog posts, guides, and explores an ever-growing range of products.

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