Report: Is Bat Guano Good For Weed Plants?

How To Supercharge Cannabis With Bat Guano
January 14, 2020

Bat guano has often been described as a cannabis superfood, rich in essential nutrients. Like Spinach to Popeye, bat guano fertilizer can seriously improve the strength, vigor and overall health of your cannabis plants. Who doesn’t want buds like giant biceps? The long list of bat guano nutrients includes nitrogen, phosphorous and potassium – three key ingredients to a successful cannabis grow.

But what is bat guano? Can anyone learn how to use bat guano? How often should you feed your weed with bat guano? Is guano enough for weed, or just a supplement? This editorial will explore both how to use bat guano for weed and when to use bat guano for weed, looking at the pros, cons, history and modern applications of guano fertilizer.

What Is Bat Guano?

They’re probably not the most well-liked member of the animal kingdom, but bats play a crucial role in ecosystems throughout the world. Some bats help control insect populations while others contribute to the pollination of vital flowers and plants. They also poop gold.

The accumulated fecal matter of bats, known in horticulture as guano, builds up (sometimes over centuries) on the floors of roosting caves. It slowly composts, developing high levels of nutrients vital to plant life. The contrasting diets of different bat species means diversity of use and application, while other sources of guano can be found in coast-dwelling seals and seabirds. Guano is hugely popular with organic growers, being both more effective and safer than the most chemical fertilizers. Bat guano can be a great alternative to some of the most popular fertilizers for marijuana plants.

History Of Guano

Guano, or “wanu” in the ancient Quechuan language, has been used in cultivation since ancient times. For over 1500 years, it was regarded as a highly-prized fertilizer by the Andean people of South America.

The rulers of the Inca empire restricted access to guano, dishing out the death penalty to anyone who disturbed their rich guano deposits.

During the 19th century, bat guano became a reason for war as well as expansion. In 1864, Spain seized the guano-rich Chincha Islands that belonged to Peru, leading to the two-year-long Spanish-South American War. Then, a decade after the conflict ended, the US Congress passed the Guano Island Act, allowing Americans ownership of unclaimed islands. More than 50 were claimed in the Caribbean and the Pacific.

Apart from agriculture, guano was also used to make gunpowder and explosives due to its abundant saltpeter (Potassium Nitrate) content. It helped the United States in their 1812 war against the United Kingdom. Then, a couple of decades later, it was again put to service by the Confederacy in the American Civil War.

Chincha "Guano" Island
Bat Guano was originally used to make weapons as opposed to fertilizer

Bat Guano For Weed Plants: A Perfect Match?

Like all living organisms, plants need nutrients to survive – this is why bat guano for cannabis is a great match. It contains both the macro and micronutrients essential for healthy growth, development, and fruit production. A good bat guano fertilizer for weed can depend on the diet of the particular bat species. For instance, insect-eating bats produce guano with high levels of nitrogen while fruit-feeders yield high phosphorus guano. Such a range in nutritional value means growers can choose bat guano for the flowering stage, veg stage, and even seedling stage. This means you can spend less time worrying about how to avoid nutrient deficiencies.

What Macronutrients Can Be Found In Bat Guano?

To achieve optimal growth, development and the ability to self-repair, plants need different macronutrients in varying amounts. In the case of cannabis, these are nitrogen, phosphorus, and potassium (NPK).

  • Nitrogen (N) –The main component of chlorophyll and amino acids, nitrogen ensures the healthy above-the-soil maturation of burgeoning stems and leaves.
  • Phosphorus (P) – An essential element for photosynthesis that promotes healthy root growth and resin production.
  • Potassium (K) –A bacteria and mold resistance booster, it strengthens stems and branches while playing a vital role in the use of air and light.

Macronutrients are essential to every phase of plant growth. However, different stages require varying proportions and combinations of NPK. Bat guano with high nitrogen content is ideal during the vegetative stages. On the other hand, phosphorus-heavy guano is better for flowering. Bare in mind that, if you’re growing autoflowering weed seeds then the growth stages will be somewhat different.

What Micronutrients Can Be Found In Bat Guano?

Trace amounts of essential vitamins and minerals are referred to as micronutrients. They are as important as macronutes to an organism’s health and functionality. The best bat guano for weed will include the following:

  • Boron (B) –A mineral that contributes to the cell wall, fruit and seed development along with calcium absorption.
  • Calcium (Ca) –An element that preserves cell structure especially in the root system, facilitating photosynthesis as well as the absorption of other nutrients.
  • Iron (Fe) and Manganese (Mn) –Both function in the enzyme systems and stimulate the production of chlorophyll.
  • Sulphur (S) and Zinc (Zn) –The building blocks of protein and enzyme production.
  • Magnesium (Mg) –The key to the absorption of light or sun energy.

When To Add Bat Guano To Your Marijuana Grow

Bat guano boasts a long history as a natural fertilizer and is well-known as such, but it has more than one horticultural application.

Bat guano fertilizer
Bat guano for weed plants: more than just a fertilizer
  • Fertilizer. Compared to other manures, bat guano is much more potent. It can be worked into the soil, used as a top dressing or made into a tea for deep root feeding.
  • Fungicide. Bat guano makes an effective fungicide when applied to plants as a foliar (through the leaves).
  • Soil Enhancer. Bat guano enhances the quality and performance of soil. It can bind overly fluffy soil or loosen dense mud, while increasing water retention. Since it won’t easily drain away, its effects last longer than most chemical fertilizers.

Is Bat Guano Good For Weed Plants?

Bat guano is well-regarded in both organic and conventional growing circles. It’s fast-acting, virtually odorless, adaptable in every phase of plant growth and produces long-lasting effects. Positive features also include:

  • Essential nutrients
  • Improvements to soil health (beneficial microflora and microbes)
  • pH balance for better nutrient absorption
  • Longer term nutrients through slow-release
  • Accelerated decomposition of exhausted materials and active compost
  • Removal of toxic elements from the soil
  • Control and prevention of nematode attacks or infestation
  • Richer, tastier flowers

Even The Best Bat Guano Has Its Drawbacks

Bat guano cannabis may taste better, and there is no doubting guano as a fertilizer, but are there cons to all the pros? Well, bat guano for sale carries quite the price tag, and it can be difficult to source, but what else?

The Ecological Impact Of Using Bat Guano For Growing Weed

Improper bat guano harvesting can destroy ecosystems. As the demand for the product increases, reports of unacceptable mining activities have also shot up. The bat’s natural habitats, nesting grounds and sources of food have been destroyed or heavily disrupted. Some of the adverse results are:

  • Disruption of the bat population caused by cave structure changes that affect the airflow.
  • Diminishing biodiversity due to the use of pesticides to kill and drive away cave-adapted invertebrates.
  • Loss of paleoclimatic records and evidence of environmental changes (naturally collected by the fecal accumulation).

The Health Hazards Of Mining Guano

Workers in guano caves are vulnerable to Histoplasmosis due to their constant exposure to bats and bat dung. Caused by a fungus called Histoplasma capsulatum, the disease is airborne and can be transmitted by spores from bat droppings and contaminated soil. The infections are often mild with minor influenza-like symptoms or no symptoms at all. That said, in some rare cases, histoplasmosis can cause high fever, pneumonia, blood irregularity or even death.

For safety reasons, it’s best only to use commercial bat guano products from responsible sources. Never try to harvest it yourself.

When And How Do You Use Bat Guano For Weed?

To supercharge cannabis plants, use bat guano as a nutrition source and protective agent, as well as a soil supplement.

Bat Guano Fertilizer

Bat guano can be applied to plant cultivation in various ways as it comes in liquid, pellet, and powdered form. It can be directly blended to the soil, watered on cannabis as a compost tea or worked into the base by digging it in.

Bat Guano Tea For Weed

Using bat guano as a tea is the most convenient way of incorporating the material in cannabis growing. It also does not require the use of any difficult-to-access components.


  • 1 tablespoon of bat guano
  • 1 liter of water (warm and non-chlorinated)


  1. Add the guano while stirring the water.
  2. Let it sit overnight. If using city chlorinated, allow the chlorine to dissipate by leaving it in an open container for the duration.
  3. Apply the final product directly to plants. To use as a foliar spray, apply the tea using a fine mist sprayer before dusk or early morning. For root application, spray it at the root area and water properly to clear its way through the roots for proper absorption.

Bat Guano Organic Soil Mix

Do not cut corners when figuring out how to grow cannabis. Always use the best materials to ensure optimal growth. This starts with employing a balanced, excellent-quality soil mix as a base.


  • 8 Large bags of High-Quality Organic Soil with a Coco and Mycorrhizae
  • 25-50 lb. Organic Worm castings
  • 5 lb. Steamed Bone meal
  • 5 lb. Bat Guano
  • 5 lb. Blood meal
  • 3 lb. Rock Phosphate
  • 3/4 cup Epson Salts
  • 1/2 to 1 cup Sweet Lime (Dolomite)
  • 1/2 cup Azomite (Trace Elements)
  • 2 tbs Powdered Humic Acid


  1. If renting a cement mixer is not possible, use a tarp and tip a few bags of the base soil into a central mound.
  2. Add the powdered nutrients to the center of the mound. Cover with more base soil.
  3. Add the bat guano and add more base soil.
  4. Continue to layer the mix with alternating powdered nutrients and base soil until everything has been added.
  5. Turn the mixture using a shovel until thoroughly blended.

Using Bat Guano To Amend Soil

Amending soil with bat guano boosts its overall quality and function. It improves drainage, aeration, structure, water infiltration, water retention and permeability, delivering a much better environment for the roots.


  1. Add powdered bat guano to the soil. Use 5 lb. for every 100 sq. ft. of medium.
  2. Dig into the surface of the soil or mulch gently to incorporate into the base. Sprinkling and leaving the powder on top of the medium will cause it to dry, clump, and be ineffective.
  3. Water-in to activate the soil-guano fusion.

Bat Guano Fertilizer

Bat guano is an all-round gift from heaven. The macro and micronutrient-packed fertilizer boosts not just plant growth but also soil quality. With numerous applications, there is no doubt why it’s so highly sought after in both commercial and home cultivation. Source it responsibly, use it sparingly and the benefits will be HUGE.

Cannabis Cultivation