Bat guano, the accumulated droppings of bats, is a highly prized natural fertilizer source used by gardeners for centuries. This organic material is rich in beneficial nutrients and microorganisms that significantly improve soil quality and plant health. Its primary benefit lies in its potent, readily available nutrient content, particularly phosphorus, which supports robust root growth and prolific flowering. Because bat guano is so concentrated, it must be properly diluted into a liquid solution, often called “guano tea,” to prevent the risk of burning or over-fertilizing plants.
Determining Guano Type and NPK Profile
The nutrient concentration in bat guano is not uniform, varying significantly based on the bat’s diet and the age of the deposit. Before mixing any solution, it is important to check the Nitrogen-Phosphorus-Potassium (NPK) ratio printed on the fertilizer packaging. This ratio indicates the percentage of each macro-nutrient by weight and determines the guano’s best use.
High-Nitrogen (High-N) guano, typically sourced from insectivorous bats, is ideal for the vegetative growth phase of a plant’s life cycle. These formulas often have NPK ratios such as 7-3-1 or 9-3-1, supporting vigorous leaf and stem development. Conversely, High-Phosphorus (High-P) guano, often from fruit-eating bats and older cave deposits, promotes flowering and fruiting. These bloom-boosting varieties may show NPK values like 0-7-0 or 1-14-0, delivering the phosphorus required for energy transfer and bloom formation.
Standard Dilution Ratios for Bat Guano Tea
The amount of bat guano used per gallon of water depends on the guano’s NPK ratio and the desired application strength. A general rule is to start with a conservative amount, as it is safer to under-fertilize than to risk nutrient burn. The following ratios provide a safe starting point for a one-gallon batch.
For a standard, general-purpose soil drench, use 1 to 2 tablespoons of powdered guano per gallon of water. This concentration is suitable for consistent feeding throughout the growing season and for younger plants. It delivers a steady supply of nutrients and beneficial microbes directly to the root zone.
When using High-P guano as a potent bloom booster during the flowering or fruiting stage, a stronger ratio of 3 to 4 tablespoons per gallon can be used. This higher concentration is reserved for mature plants that are actively drawing heavy amounts of phosphorus to support dense bloom formation.
For a light foliar spray, the mixture must be much weaker to prevent leaf scorching. A ratio of 1 teaspoon of guano per gallon of water is sufficient for this application. This provides a fast boost of micronutrients and beneficial microbes directly to the leaf surface.
Preparing and Brewing the Fertilizer Tea
Water Preparation
The method of preparation is important to ensure the nutrients are properly extracted and microbial life is preserved. Use non-chlorinated or distilled water, as chlorine can harm the beneficial microbes within the guano. If using municipal tap water, leave it in an open container for 24 hours to allow the chlorine to dissipate.
Steeping and Aeration
The guano should be mixed into warm water, but never hot, as excessive heat will kill the living microbial community. Simple steeping involves placing the guano in a mesh bag and allowing it to soak for 24 to 48 hours to passively extract the soluble nutrients.
For a more biologically active fertilizer, the solution can be actively aerated using a small aquarium air pump and an air stone. Aeration introduces oxygen, which encourages the growth of beneficial, aerobic bacteria and fungi. This process, often called brewing a “compost tea,” should run for at least 24 hours.
The finished tea must be strained through a fine cloth before application to remove all sediment. Straining prevents the solid particles from clogging spray nozzles or irrigation lines.
Application Methods and Feeding Schedules
The prepared guano tea can be applied using two main techniques. The most common is the soil drench, where the solution is poured directly onto the soil to saturate the root zone. This delivers nutrients and microbes to the roots, allowing immediate uptake and enriching the soil structure.
The second method is foliar feeding, which involves lightly misting the plant leaves with the finely strained, low-concentration solution. This allows for rapid nutrient uptake through the leaf stomata. Foliar applications are used to quickly address a specific nutrient deficiency or to deliver a microbial boost.
The timing of application should align with the plant’s growth stage and the type of guano used. High-Nitrogen guano tea is best applied during the vegetative stage, typically every two to four weeks. High-Phosphorus tea should be utilized as a supplement once the plant begins its transition into the flowering phase, and monitoring the plant’s color and vitality is the best way to determine if the current feeding schedule is appropriate.