Guano: [Fertilizer, Benefits, Nutrients and How to Prepare it]

Guano (from Quechua: wanu) is the accumulated excrement of seabirds and bats.

As manure , guano is a very effective fertilizer due to its exceptionally high content of nitrogen, phosphate and potassium – essential nutrients for plant growth. Guano was also sought, to a lesser extent, for the production of gunpowder and other explosive materials.

What is guano?

The term «Guano» is formed from natural mineral deposits made up of excrement, egg shells and dead seabird carcasses found in almost rainless and hot and dry climate regions, and the corresponding fertilizers.

Guanos are classified according to age, genesis, geographic origin, and chemical composition.

The main types are nitrogen and phosphate guanos . Phosphate guanos require a calcareous subsoil for their development, while nitrogen guanos are formed only in the special climatic conditions of the high pressure tropical belt of the subtropical border with coastal deserts.


Nutrients provided by guano

Bat guano typically has a 10-3-1 ratio of nitrogen, phosphorus, and potassium , nutrients that are essential for plant growth.

The high nitrogen content helps plant leaves turn greener in just a few days. It also helps that the guano slowly releases these nutrients, over several months.

Phosphorous helps promote seed creation and flowering, while potassium helps the plant move water and nutrients more efficiently.

Soil improvement

Bat and bird guano contain microbes that benefit the texture of your garden soil.

It also has the potential to enrich the soil and improve its drainage properties. In addition, it helps to make dense soils lighter and holds loose soils together.

In addition, guano is not easily removed from the soil, so it benefits plants much longer than inorganic fertilizers that are displaced or washed away after a single rainy day.


Bat guano supplies more than just nutrients; it also carries microorganisms that help break down dry stool.

These microbes help break down other organic materials in the soil, such as compost , and turn them into nutrients for plants. This can help improve the density of the soil, creating a texture that retains moisture and favors the roots of the plants without becoming too saturated.


Fungicide and insecticide

Bat guano tends to act as a fungicide in the soil, breaking down fungi along with other organic materials.

This helps keep plants healthy and disease free. It can also control nematodes, a nasty insect that can destroy your plants. Applying bat guano early in the season can help prevent the nematode population from exploding.

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Last update 2021-06-10 / Affiliate Links / API Images for Affiliates

How to use guano on your plants

When using the bat guano powder or pellet form, simply sprinkle around the base of your plants and water thoroughly.

You can also mix 2 or 3 teaspoons of guano in 3-4 liters of water and pour it over your plants. Bat guano tea can be used as a foliar spray or poured onto plant roots.

Collect about 300 grams of guano in cheesecloth and soak it in 4 liters of water for at least three days, then use that water to fertilize your plants.

You can pour it into the ground immediately before planting. This ensures that the soil in your garden or orchard is sufficiently prepared to provide beneficial nutrients for your crops.

Why is guano so effective as a fertilizer?

Guano is important from an ecological point of view due to its role in terms of the nutrients it provides.

Cave ecosystems, in particular, tend to be totally dependent on bats to provide them with nutrients through their guano, which supports bacteria, fungi, invertebrates and vertebrates.

Losing bats from a cave can lead to the extinction of species that depend on their guano. Guano also has a role in cave formation, as its high acidity leads to erosion.

Did you know…?
Tip: Make sure to always read the instructions on the fertilizer label before using it.

Also, if your plants show any signs of deterioration, immediately stop using the guano fertilizer. You don’t want to burn your plants with an overabundance of guano.


Where to use guano

Sprinkle guano powder around the base of your growing plant and water considerably well. You can also make guano tea and sprinkle it on the leaves of your plant to protect it from fungal diseases.

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Last update 2021-06-10 / Affiliate Links / API Images for Affiliates

What types of guano can we find?

Bird guano

Bird guano has high levels of nutrients like nitrate and ammonium. By mass, it is 8-21% nitrogen; the nitrogen content is around 80% uric acid, 10% protein, 7% ammonia, and 0.5% nitrate.

Some of the most common chemical elements in bird guano are phosphorus, calcium, and magnesium. It can react with the rocky substrate of islands such as basalt to form authentic phosphate minerals, including taranazite and leukophosphite.


Bat guano

When freshly excreted, insectivorous bat guano consists of fine particles of insect exoskeleton, which are largely composed of chitin. Elements found in high concentrations include carbon, nitrogen, sulfur, and phosphorus.

Due to the action of bacteria and fungi, fresh guano decomposes quickly, and generally loses its organic matter more quickly. Organic matter does not usually persist in a cave guano deposit at depths greater than a few centimeters.

Fresh guano contains about 2.4 to 7 times more carbon than nitrogen; the carbon to nitrogen ratio decreases or remains similar when sampling older guano.

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Fresh guano has a pH of 5.1-7.3, which makes it neutral or somewhat acidic. However, as it ages, guano becomes strongly acidic, reaching pH levels of 2.7-4.1.

Like bird guano, the acidic properties of guano and cave limestone can interact to create phosphate minerals such as blanchite, taranakite, variscite, spheniscite, montgomeryite, and leukophosphite. Other minerals found in guano are quartz, graphite, gypsum, bassanite, and mica.

Insectivorous or sanguivorous bats

The composition of guano varies between bat species with different diets.

When comparing guano from insectivores (Mexican free-tailed bats), frugivores (Rodrigues flying foxes), and sanguivores (common vampire bats), a 2007 study found that the three did not differ significantly in terms of proportions of organic matter or carbon in dry matter.

The sanguivores had high carbon in the organic matter, the sanguivorous and insectivores had high nitrogen in the organic and dry matter, and the insectivores and frugivores had high phosphorus. Frugivores had the highest carbon-to-nitrogen ratio, while sanguivores had the highest nitrogen-to-phosphorus ratio and carbon-to-phosphorus ratio.


Guano history

The guano trade in the 19th century played a pivotal role in the development of modern input-intensive agriculture, but its demand began to decline after the discovery of the Haber-Bosch process of nitrogen fixation led to the production of synthetic fertilizers.

The demand for guano spurred human colonization of remote bird islands in many parts of the world, leading to some of the earliest examples of American colonialism and the expansion of the British Empire.

The guano extraction process led to ecological degradation due to the loss of millions of seabirds. The unsustainable mining of guano in the caves alters the shape of the caves, causing the bats to leave the henhouse.


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Last update 2021-06-10 / Affiliate Links / API Images for Affiliates

Guano mining also led to the mistreatment and enslavement of workers such as Chinese immigrants, Native Hawaiians, and the African diaspora.

The most important nitrogen guano is Peru-Guano, which has been used for over 2000 years as an agricultural fertilizer in Peru.

In Europe, the application of guano as a fertilizer emerged in 1840 as a «guano boom» and lasted until the early 20th century, when guano was replaced by industrially manufactured fertilizers. Only a small amount continues to be exported to Europe as an additive to organic / mineral fertilizers, more for image reasons than effect.

Did you know…?
The guano trade was very dangerous.

If a clipper ship, the fastest way to travel in the mid-19th century, was heading from the east coast of America to Peru, it would first have to navigate the dangerous waters of Cape Horn.

To navigate dangerous seas, ships used charts and other navigational tools.

However, there was also danger in the islands from which the guano was extracted. Workers, most of them Chinese servants, mined the guano, which was backbreaking and dangerous work. Because guano dust filled the air with ammonia, both miners and sailors were vulnerable to toxic and asphyxiating gases.

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