Although the word 'guano' is used to refer to both bat and seagull dung, and is defined in the dictionary that way, it originally came from the Quichua language of the Inca civilization and means 'the droppings of sea birds'.

Guano begins its 'life' as living plants. Eaten by insects that are eaten and digested by bats, or fish that are eaten and digested by birds, it is deposited on the floors of caves and on rocks. Add some carcasses, feathers, eggshells, sand and some beetles and microbes to process the waste and what's left is one of nature's best fertilisers.

The Value of Guano

The Incas used to collect guano from the coast of Peru and use it as a soil enricher. They treated the guano as a valuable material by restricting access to it and punishing any disturbance to the birds with death.

Guano from Peru is considered the best in the world. The Peruvian current brings cold water from Antarctica to the Equator along the coast, and the combination of cold water and warm air prevents rain from falling. The islands along the coast are baked in the sun, and the lack of rain means that the nitrates in the guano do not evaporate or leach into the rock, so the fertiliser maintains its effectiveness.

The United States also recognised the value of guano by passing an Act in 1856 that gave protection to any citizen that discovered a source of guano. The discoverer was able to take possession of unclaimed land that contained guano, and was entitled to exclusive rights to the deposits. The catch was that the guano could only be removed for the use of the citizens of the United States.

By the end of the 19th Century, artificial fertilisers made guano less important, although it is enjoying a return to favour for organic gardeners.

Nutritional Value and Uses

As the source of guano is so varied, the nutrients in guano vary too. Sea birds eat small fish; seagulls also scavenge. Bats of one species eat fruit, of another, insects. Guano can also be found fresh and fossilised. All these are factors in the amount of nutrients in the fertiliser, but an average would be 15% nitrogen, 9% potassium and 3% phosphorous.

Guano can be used on indoor and outdoor plants, applied the same way as any other fertiliser. It can also be used by hydroponic gardeners, by mixing it with water. Added to topsoil it can be used for laying lawns, turf and seed, and for planting trees and shrubs. Guano that is heavy in nitrogen is good for growth, when heavy in phosphorus it is good for developing buds.

Properties of Guano

• Soil builder - improves the texture of the soil.

• Lawn treatment - promotes healthy colour and growth.

• Soil cleanser - microbes help to clear any toxins in the soil.

• Fungicide - when fed to plants through the leaves.

• Nematocide - decomposing microbes help control nematodes¹.

• Compost activator - microbes speed up decomposition.