Bat Guano Fertilizer: NPK, Safety and Cost per Pound of N

Bat guano fertilizer is dried, partly decomposed bat droppings sold as an organic source of nitrogen and phosphorus. A Kansas State University table lists bat guano at about 10% nitrogen, 4.5% phosphoric acid and 2% potash, but published analyses range widely, from a high-nitrogen 10-4.5-2 type to a 0-5-0 phosphate type. The label on your bag, not the word “guano”, tells you which one you have.

This guide shows what is in the bag, the one real health risk (dust that can carry the histoplasmosis fungus), how the US organic rules treat guano, how to apply it, and how to compare its cost per pound of nitrogen with other organic fertilizers using the calculator below.

What is bat guano used for?

Gardeners and growers use bat guano in three ways: mixed into soil before planting, scattered around plants during the season as a top-dressing, or steeped in water and poured on as a liquid feed. High-nitrogen guano feeds leafy growth. Phosphate-rich guano is used when roots, flowers and fruit need more phosphorus.

Guano comes from the floors of caves and from roost structures where large colonies sleep. Insect-eating bats and fruit-eating bats leave different droppings, and old deposits change as they age, wash and break down. That is why two bags called “bat guano” can have very different numbers on the label.

The University of Washington’s Miller Library notes that bat guano supplies supplemental nitrogen, at about 12 percent nitrogen, with an N-P-K ratio of roughly 8-5-1.5 in the analysis it cites from Oregon State University (University of Washington Miller Library, Safety of bat guano). Treat any single ratio as a typical example, not a promise.

What else bat poop is used for

Fertilizer is the main modern use, but it was not always the most important one.

• Gunpowder. Thousands of years of bat guano left the dirt of Mammoth Cave in Kentucky rich in calcium nitrate. Miners leached the dirt with water and turned the nitrate into saltpetre for black powder. The trade boomed during the War of 1812, when the British blockade made imported gunpowder hard to get, as the National Park Service account of saltpetre mining at Mammoth Cave describes.
• Commercial fertilizer mining. At what is now Carlsbad Caverns in New Mexico, guano was dug from the Bat Cave in the early 1900s and shipped as fertilizer, according to the Western National Parks Association history of Carlsbad Caverns.
• Food for cave life. No plants grow in the dark, so droppings are an important food source in many caves. Insects, mites, fungi and bacteria live on them. This is one reason why digging guano from active roosts is restricted in many places.
• Gardens and greenhouses. Today the main buyers are home gardeners, organic vegetable growers and container growers.

Bat guano fertilizer NPK: what is in the bag

Extension tables do not agree on one bat guano analysis, because the material itself varies. The chart below sets four published figures side by side.

Chart

Nitrogen in bat guano, by published source

% nitrogen listed for bat guano by four US university sources

Sources: Kansas State University, Approximate Composition of Select Natural Fertilizer Materials; University of Maryland Extension, Table B-11; UW-Madison Extension Kenosha County, Common Organic Fertilizers.

So there are, broadly, two kinds on the shelf:

• High-nitrogen guano. Fresher deposits from insect-eating bats often. Best for leafy growth early in the season. Numbers like 10-4.5-2 or 8-5-1.5 fall in this group.
• High-phosphate guano. Older, more weathered deposits. Most of the nitrogen has gone, and phosphorus is left. Best for root and flower stages. Labels such as 0-5-0 fall in this group.

California has set rules for what can be sold as bat guano. From 1 January 2018 (new labels; renewals were phased in), a product must be partly decomposed bat excrement with more than 40% organic matter “as is”, it is treated as a source of nitrogen, and it may contain up to 6% available phosphate. Registrants must document their supplier and give a lab analysis, and the state may ask for a bat DNA test. The term “fossilized bat guano” is no longer allowed on labels (California Department of Food and Agriculture, Notice to Fertilizing Material Licensees, May 2017). Other states and countries have their own fertilizer label rules, so check what applies where you farm.

Nutrient by nutrient

• Nitrogen. The main reason to buy high-nitrogen guano. Kansas State lists it at 10% N, far above dried cow manure at 1.3% in the same table.
• Phosphorus. Supports roots, flowers and fruit. Phosphate-type guano is mostly phosphorus.
• Potassium. Low in every analysis above (0-2%). If your soil test shows low potash, add a separate potassium source.
• Organic matter and minerals. Guano also carries organic matter, calcium and other minerals. The extension tables above do not give percentages for these, so do not count on a set amount.

If the exact numbers matter for your crop, ask the supplier for the current batch analysis or send a sample to an accredited lab. University of Maryland Extension asks growers to check with their certifying agency before using any listed material, as organic status can change.

How bat guano compares with other organic fertilizers

Bat guano is one of several concentrated organic nitrogen sources. In the Kansas State table, its 10% nitrogen sits close to fish meal (10%), below dried blood meal (13%) and feathers (15%), and well above manures.

Chart

Nitrogen in selected organic fertilizers

% nitrogen, approximate composition, one table

Concentration matters because it sets how much product you must carry and spread. At 10% nitrogen, 10 pounds of guano supply 1 pound of nitrogen. At 1.3%, you would need about 77 pounds of dried cow manure for the same pound. Bulky manures bring much more organic matter, though, so they do a different job.

Release speed also differs. University of Maryland Extension rates bat guano as “medium” availability, dried blood as “medium rapid” and fish meal as “slow”. UW-Madison Extension lists its 0-5-0 guano as slow release. In plain terms: guano is not as fast as a soluble synthetic, and not all of its nitrogen is available to plants in the first weeks.

Bat guano fertilizer dangers: what the safety data says

The main documented risk is not touching guano or putting it in soil. It is breathing in dust. Dry dust from soil mixed with bird or bat droppings can carry spores of the fungus Histoplasma, which causes histoplasmosis.

The US Centers for Disease Control and Prevention (CDC) page on histoplasmosis says the fungus lives in soil and spreads in bird and bat droppings mixed into soil. In the United States it is found mainly in the central and eastern states. Most people who breathe in the spores do not get sick. When symptoms do appear, they usually start 3 to 17 days after exposure and look like a flu or chest infection. People with weakened immune systems are at higher risk of serious illness.

The University of Washington Miller Library advises wearing a dust mask when opening bags of soil amendments and spreading them, to avoid breathing in fungal spores. It also notes that people harvesting guano in caves face wider risks and need masks, gloves and good hygiene.

Simple precautions:

1. Dampen it first. Wet guano makes far less dust than dry guano.
2. Wear respiratory protection. At minimum a dust mask for opening and spreading bags; a properly fitted respirator for bulk handling or confined spaces such as sheds, attics and grow rooms.
3. Work outside or with good airflow. Avoid pouring dry guano indoors.
4. Wash hands and tools. Treat guano as you would any manure.
5. Buy registered products. Registered fertilizers come with a label, a guaranteed analysis and a traceable supplier.
6. Never dig in bat roosts or caves. This is the highest-risk activity, and it disturbs bats.

This is general safety information, not medical advice. If you develop fever, cough or chest pain after handling guano or droppings, see a doctor and mention the exposure. Follow the product label and your local workplace safety rules.

Food safety on edible crops

Guano is a manure, so the same food safety logic applies. The US organic rules (below) set waiting periods between applying raw manure and harvesting food crops. Even outside organic systems, keep guano and guano tea off the edible parts of leafy greens and root crops close to harvest, and follow your local food safety guidance.

Is bat guano allowed in organic farming?

Bat guano can be used in certified organic production in the United States, but with restrictions. University of Maryland Extension lists bat guano as “Restricted”: allowed guano is decomposed and dried deposits from wild bats or birds, and it must meet the requirements for using raw manure.

Those requirements are in the USDA organic regulations at 7 CFR 205.203, the soil fertility and crop nutrient standard. Raw animal manure must be composted, or applied to land used for crops not for human food, or incorporated into the soil:

• at least 120 days before harvest of a crop whose edible part touches the soil surface or soil particles; or
• at least 90 days before harvest of a crop whose edible part does not touch the soil.

The USDA Agricultural Marketing Service guide to manures and composts calls this the 90-120-day rule. It also notes that certifiers may ask for tests if a manure source may be contaminated.

In practice, many growers look for a product on the Organic Materials Review Institute (OMRI) lists, then confirm with their certifier. A product’s listing can change, so check before each season. “Natural” on a bag is not the same as approved for certified organic use. Our page on the differences between sustainable and organic farming explains why those labels are not interchangeable.

Outside the US, organic rules differ. In Canada, the UK, the EU, Australia and New Zealand, ask your certification body whether a given guano product is permitted and under what conditions.

Is bat guano valuable? What sets the price

Bat guano is sold as a premium input in small bags for gardens and greenhouses, and in larger bags for farms. There is no public market price series for it. Prices depend on the supplier, bag size, analysis, origin and shipping. So the useful question is not “what does a bag cost” but “what does a pound of nitrogen cost”.

To work that out, divide the price per pound by the nitrogen share. A bag at 10% nitrogen means each pound of product carries 0.1 pound of nitrogen. If that pound costs US$3, the nitrogen costs US$30 a pound. Do the same for blood meal, feather meal or fish meal and you have a fair comparison. The calculator below does this for you.

For context, synthetic nitrogen is much cheaper per pound of nitrogen, though it carries no organic matter and is not allowed in certified organic systems. The World Bank tracks fertilizer prices in its monthly “Pink Sheet”. In its October 2026 edition, urea (Middle East, f.o.b. spot) averaged US$399 per tonne in July-September 2026, after US$694 in April-June 2026 (World Bank Commodity Price Data, October 2026). These are bulk export prices, not the price a farmer pays at the dealer.

Bat guano vs synthetic fertilizer

Bat guano cost per pound of nitrogen calculator

Enter your garden or field area, the nitrogen you want to apply and the prices you were quoted. The calculator shows how much guano you need and compares its cost per pound of nitrogen with a second organic product such as blood meal. The default numbers are examples only, set so both products cost about the same per pound of nitrogen.

Chart

World urea and DAP prices by quarter

US$ per tonne, quarterly averages; urea f.o.b. Middle East, DAP f.o.b. US Gulf

Try the numbers for your own farm below.

How to use bat guano: application methods

Always follow the rate on your product label. Guaranteed analysis varies by supplier and batch, so a rule of thumb from one bag does not fit another. These methods apply to most products:

1. Test the soil first. A soil test tells you whether you need nitrogen, phosphorus or neither. Your state or provincial extension service can point you to a lab.
2. Pick the type. High-nitrogen guano for leafy growth; high-phosphate guano for roots, flowers and fruit.
3. Pre-plant. Mix the guano into the top few inches of soil or into the planting furrow a little before planting.
4. Top-dress or side-dress. Scatter it around established plants during the season and water it in. Keep it off leaves.
5. Guano tea. Steep guano in water and apply as a soil drench. This is common in containers and greenhouses. Follow the label’s dilution, and keep it off edible parts near harvest.
6. Watch the crop. Look for greener, stronger growth in the weeks after application. Too much nitrogen gives soft, leafy growth and can burn roots.

Concentrated nitrogen sources can damage seedlings if they touch roots in high amounts. Start at or below the label rate, especially in pots. This is general guidance; follow the label and local rules, and ask your extension service for crop-specific rates.

Bat guano for cannabis and container growing

“Bat guano weed” searches usually mean cannabis growing. Container and indoor growers use guano for the same reasons as vegetable growers: concentrated nutrients from an organic source. The same rules apply. Match the type to the stage (higher nitrogen in leafy growth, higher phosphorus in flowering), follow the label, and handle dry guano with a mask in grow rooms, where dust does not clear. Growing cannabis is legal only in some places; check the law where you live.

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Bat guano and weed seeds

The other meaning of “bat guano weed” is whether guano brings weed seeds into your beds. Insect-eating bats eat insects, not seeds, so their guano is not expected to carry the seed load that raw livestock manure can. Fruit-eating bats can pass seeds, though. No extension source reviewed here gives a count of viable weed seeds in commercial guano.

If clean media matter, as in seed-starting mixes, ask the supplier how the guano was processed, use a product with documentation, and watch new beds for odd seedlings.

Bats, sustainable sourcing and supply

Guano supply depends on healthy bat colonies. Bats are worth far more to farmers alive and eating insects than as a fertilizer source. A study in Science by Boyles and colleagues estimated that the loss of bats in North America could lead to agricultural losses of more than US$3.7 billion a year (Boyles et al., Economic Importance of Bats in Agriculture, Science, 2011). The authors linked the threat to white-nose syndrome and wind turbine deaths.

That gives growers good reasons to buy with care:

• Ask where it came from. The University of Washington Miller Library suggests asking suppliers where they get their guano and whether it is harvested without harm to bats, their habitat or the health of harvesters.
• Prefer documented origin. California requires proof for any origin claim on the label.
• Avoid disturbing roosts. Never collect guano from caves, barns or attics where bats live. Many bat species are protected, and disturbing them can be illegal.
• Use it where it counts. Because supply is limited, guano makes most sense in small, high-value uses such as gardens, greenhouses and specialty crops, not as a bulk field fertilizer.

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Where bat guano fits in a fertility plan

Bat guano is one input in a soil fertility program, not a replacement for soil testing. On a field scale, compost, manure, cover crops and, in conventional systems, synthetic fertilizers supply most nutrients. Guano fills a niche: a concentrated, organic-approved boost when you need it.

A simple plan for using it:

• Base the rate on a soil test and your crop’s needs.
• Use bulky compost or manure for organic matter, and guano for concentrated nitrogen or phosphorus.
• Add potassium separately if the soil test calls for it.
• Check results in the season, not only at harvest.

Checking results in the season is where satellite crop monitoring helps on larger plots. Vegetation index maps show whether the canopy is greening up evenly after a fertilizer change, and where it lags. The Farmonaut Satellite + AI Farm Monitoring System shows these maps for your own fields; they point to where to look, and a field visit and soil test confirm the cause.

▶ How satellite NDVI maps show crop stress across a field before it is easy to see from the ground. · 4:09

FAQ

What is bat guano fertilizer used for?

It is used as an organic source of nitrogen or phosphorus, mixed into soil before planting, scattered around plants during the season, or steeped in water as a liquid feed. Kansas State University lists high-nitrogen bat guano at about 10-4.5-2.

What are the dangers of bat guano fertilizer?

The main risk is breathing in dust that can carry the Histoplasma fungus. The CDC says most people who breathe in the spores do not get sick, but symptoms can start 3 to 17 days later. Dampen guano, wear a mask or respirator, and work with good airflow.

What is the NPK of bat guano?

It varies. Published extension analyses include 10-4.5-2 (Kansas State), about 8-5-1.5 (University of Washington), 5.7-8.6-2 (University of Maryland) and 0-5-0 (UW-Madison Extension). Use the guaranteed analysis on your bag.

Can I use bat guano on an organic farm?

In the US, yes, with restrictions. It must meet the raw manure rules in 7 CFR 205.203, which include 90- and 120-day gaps before harvest unless it is composted. Check the product’s OMRI status and ask your certifier.

Is bat guano better than blood meal?

Not on nitrogen alone: Kansas State lists dried blood meal at 13% nitrogen and bat guano at 10%. Guano also brings phosphorus. Compare products on cost per pound of nitrogen with the calculator above.

Does bat guano contain weed seeds?

Guano from insect-eating bats is not expected to carry many seeds, but guano from fruit-eating bats can. No extension source reviewed here gives seed counts, so ask the supplier how it was processed.

The bottom line on bat guano

Bat guano is a useful, concentrated organic fertilizer, but it is not one standard product. High-nitrogen types run around 10% nitrogen in the Kansas State table; phosphate types may have almost none. Read the guaranteed analysis on the bag, compare cost per pound of nitrogen with other organic options, handle dry guano damp and with a mask, follow the 90-120-day rule on organic food crops, and buy from suppliers who can show where it came from.

Related pages on our site: essential plant nutrients, fertilizer innovations, product traceability, carbon footprinting, large farm management, web app, satellite data API and API developer docs.