Bat guano, or bat droppings, is an organic fertilizer that can boost soil nutrients and help you have stronger plants. There are many benefits to using bat guano as fertilizer, but there are also concerns and scare stories.
The natural fertilizer has been used for centuries in farming and is still used today by organic gardeners and farmers. Thankfully, it is now available as a pre-formulated dried fertilizer, so you don’t need to venture deep into caves to collect it yourself. These products are used as a soil amendment, added as a top dressing, or turned into a liquid guano tea.
Bat guano remains a beneficial fertilizer for a vegetable garden, flower border, or container garden, and this bat guano at Amazon is even OMRI-listed for organic gardening. If you are concerned about the safety of using bat guano as fertilizer, there are a few key points to remember. I spoke to some experts about bat guano and how best to use it in a garden.
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What Is Bat Guano?
(Image credit: Stan Tekiela Author / Naturalist / Wildlife Photographer / Getty Images)
There is no sugar-coating it: bat guano is the poop produced by bats. It accumulates quickly from large colonies, and commercial companies harvest it from caves to convert it into fertilizer.
There are environmental issues with removing guano from a cave. It should be done properly and not interfere with the bats’ ecosystem, which causes them to abandon a roosting site.
Gardeners looking for a new organic fertilizer for flowers or vegetables can buy packaged bat guano fertilizers or collect small amounts from bat boxes or bat houses by placing a container underneath. It is never recommended to enter caves to harvest it yourself.
You may wonder, is bat guano fertilizer safe? The main health issue with bat guano is a fungus called Histoplasma capsulatum, which causes Histoplasmosis in humans. Scott Kent, a soil microbiologist and worm farmer, warns that collecting any bat guano potentially exposes you to the fungus.
He adds: ‘Thankfully, commercially produced bat guano has standards for safety for preventing disease, is shelf-stable in its packaging, and is safe to handle – although you should still wear gloves and avoid inhaling any of it or getting it in your eyes.’
Check the packaging on any bat guano product to ensure it is properly processed under USDA National Organic Program guidance and regulations.
How to Use Bat Guano as Fertilizer
You can use bat guano on flowers, vegetables, and fruits, but with caution. Bat guano contains essential nutrients that plants need for healthy, strong development. It is often high in nitrogen, which helps plants put on lush green growth. It also contains good levels of phosphorus for root development and potassium for flowers and fruits.
However, the exact NPK levels can vary depending on what the bats have been eating and any additional materials added to the product.
‘Some guano fertilizers are relatively high in nitrogen, while others are processed or formulated to provide more phosphorus,’ warns Heidi Grasman, a professional gardener and the co-owner of Garden Crossings. ‘That makes reading the NPK analysis on the package especially important.’
Nitrogen-rich bat guano benefits plants early in the season to support vegetative growth. On the other hand, phosphorus-rich bat guano helps develop flowers and fruits later in the growth cycle.
Use Bat Guano as a Soil Booster
(Image credit: Future/Ruth Hayes)
Gardeners can add bat guano to the soil before planting and mix it into the top few inches of soil to boost the soil’s nutrient levels. It makes an excellent supplemental slow-release feed to use along with compost in the ground or containers, rather than as a standalone fertilizer to improve soil health.
Siobhan Shaw, sustainable gardening expert and founder of Growing to Give, says bat guano makes an ‘excellent organic fertilizer when used correctly’ with compost to add nitrogen to the soil and have healthy, productive plants.
‘Compost is the foundation of my garden because it improves soil structure, moisture retention and feeds the soil biology,’ she adds. ‘I think of guano as a concentrated nutritional boost when plants actually need it.’
Established plants in the ground, raised beds, or containers can also be side-dressed during the growing season for a fast-acting dose of nutrients. Sprinkle the recommended amount around the soil, taking care not to get any on the stems or leaves, and water it in thoroughly.
Using it correctly includes sticking to the manufacturer’s recommendations. As bat guano is highly concentrated, you can easily over-fertilize plants.
‘If you apply too much, you can give plants more nutrients than they can use and potentially damage roots,’ warns Dr Russell Sharp, a plant scientist and founder of Eutrema. ‘It’s especially easy to overdo concentrated feeds in pots, where there’s less soil around the roots.’
Use Bat Guano as a Liquid Feed
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Processed bat guano products can be used as a liquid fertilizer to feed plants through the growing season. Check the recommended amounts of product and water, and let the mixture steep for 24-48 hours, stirring occasionally.
The brew will have a strong, undesirable odor. The liquid can be used to water the plants and give them a fast-acting dose of nutrients or applied as a foliar spray.
Dr Russell Sharp warns of the dangers of making a liquid feed from any guano you have collected. ‘I wouldn’t make fertilizer tea from raw droppings,’ he claims. ‘You don’t know its nutrient strength or what organisms may be present, so there’s no good reason to take that risk when processed gardening products are available.’
When making a brew to use bat guano as fertilizer, use the mix quickly rather than storing it for extended periods. And again, always use it at the recommended rates, as bat guano can burn plant roots when applied excessively.
Shop Bat Guano Fertilizers
A final way to use bat guano as fertilizer is to add small amounts to your compost heap. However, wear gloves, eye protection, and a mask when handling it, and ensure your compost heap gets hot enough to kill any pathogens – ideally 140-160°F (get a compost thermometer from Amazon to check).
If your compost heap is not heating up, the ratio of brown and green ingredients may be off, or the pile might be too dry. Turning, watering, and adding more green ingredients can help to boost a dry pile.
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