Guanos have been used for centuries as a fertilizer. The Andean people of South America have used guano as a fertilizer for more than 1,500 years. The Incas placed so much value on guano they restricted access to it under the penalty of death to anyone who disturbed the guano producing birds. Control over islands laden with seabird guano were the driving issue in the Chincha Islands War of 1864 to 1866 between Peru and Spain. Fortunately, Buried Treasure has made seabird and bat guano readily available by bag or bottle so you don’t have to go to war or extreme measures to get what you need for your garden.

The two main types of Guanos available on the market are, bat guano and seabird guano. Although these products may appear similar, there are also some substantive differences. Seabird guano tends to be high in nitrogen, phosphorus and calcium because of their high protein fish-based diet. Bats have two main food sources, fruit and insects. Fruit eating bats tend to produce high levels of phosphorus, while insect eating bats produce guano with higher nitrogen levels. Most guanos on the market have very different ranges when it comes to their NPK’s. This is due to several factors concerning the diets of these animals. Weather and seasonality have a huge effect on the NPK levels of guanos. As weather patterns and seasons change, bats and seabirds are forced to eat what is available to them. Because of this, the stability of measuring NPK’s becomes difficult. Some years guanos extracted from the same locations can have huge variances in their elemental makeup.

Another distinctly different guano are those that are void of (or contain low amounts of) nitrogen. These can be found in both bat and seabird guanos, and is generally due to the guano being aged or fossilized. The nitrogen is lost over time either through leaching and or volatilization. The fossilized guano has been processed over time by microbial action and pressure, essentially mineralizing it. 

Besides N-P-K, guanos contain various micronutrients and natural microbes that can be beneficial to increase quantity and diversity of soil life. Top dressing, blending Buried Treasure Guanos or watering in Buried Treasure Liquid Guano can help to activate these dormant microorganisms in a grower’s media.