Manure tea, a liquid fertilizer derived from soaking manure or compost in water, is a traditional method for delivering nutrients and beneficial microorganisms to garden plants. This extract provides a readily available source of soluble nutrients like nitrogen, phosphorus, and potassium, alongside a diverse microbial community. Understanding the longevity and potency of this product is important to maximize its effectiveness. The shelf life of manure tea is surprisingly short due to its reliance on living biological processes, meaning timing its use is a primary concern.
The Optimal Window for Use
The usable life of manure tea depends heavily on the creation method: actively aerated or passively brewed. Actively aerated tea (AAT) is produced by vigorously bubbling air through the mixture, cultivating a large population of beneficial aerobic microbes. Since these organisms are highly oxygen-dependent, AAT must be used quickly once aeration stops.
The optimal window for applying AAT is typically very short, ranging from four to 36 hours after the air pump is turned off. Using the tea within this period ensures the highest concentration of live, active microorganisms. Passively brewed tea, often called manure extract, is simply steeped without continuous aeration. This passive method results in a lower microbial count and a slightly more stable, but still limited, shelf life. Passive tea should generally be applied within one to three days of brewing.
Factors Determining Biological Decline
Manure tea has a limited shelf life because it is a highly active biological system where beneficial organisms quickly face survival constraints. The primary factor driving this decline is oxygen depletion. The vigorous growth of aerobic microorganisms during brewing rapidly consumes the dissolved oxygen in the water.
Once oxygen levels drop, the environment quickly becomes anaerobic, causing the death of beneficial microbes and the proliferation of undesirable bacteria. Temperature also plays a significant role; warmer temperatures accelerate microbial metabolism, leading to faster oxygen consumption and a subsequent population crash. As temperatures rise, the window of usability shortens.
The third factor is the exhaustion of available nutrients extracted from the manure or compost. Beneficial microbes feed on these soluble compounds, and once this food source is consumed, their population cannot be sustained. This nutrient exhaustion leads to a sharp reduction in microbial activity, making the tea less effective.
Storage Methods to Slow Degradation
While stopping the biological decline of manure tea is difficult, several methods can temporarily slow degradation. Temperature control is the most effective strategy, as lower temperatures slow microbial metabolism and oxygen consumption. Storing the tea in a refrigerator or a cool, shaded area (ideally between 50°F and 68°F) can extend usability by a few hours.
Using the correct container primarily prevents contamination rather than slowing biological decline. Non-porous containers with tight-fitting lids should be used to prevent foreign material from entering. However, a sealed container traps carbon dioxide, hastening anaerobic conditions. This method is only recommended for very short-term storage or if re-aeration is an option.
Periodic re-aeration is the most direct way to temporarily prolong the life of actively aerated tea. Using a small aquarium pump and air stone to briefly reintroduce oxygen every few hours can delay the switch to anaerobic conditions. While this technique buys time, it only slows the inevitable decline in the tea’s biological diversity and nutrient availability.
Identifying Manure Tea Spoilage
The primary indicator that manure tea has spoiled is a change in its sensory characteristics, particularly its odor. Fresh, healthy tea should have a mild, earthy, or slightly yeasty aroma, similar to healthy soil. A foul, rotten egg, or sewage-like smell indicates the tea has gone anaerobic.
This unpleasant odor is caused by volatile organic compounds, such as hydrogen sulfide, which are byproducts of anaerobic decomposition. This microbial shift is undesirable because anaerobic bacteria can produce phytotoxic compounds that harm plant tissues. Visually, a spoiled batch may also show changes, such as a slimy surface film or excessive sludge at the bottom of the container.
Using anaerobic tea is not only less beneficial but can be detrimental to plants. The presence of undesirable pathogens, such as E. coli or Salmonella, is also a risk when the tea has sat without oxygen. When these sensory cues are present, it is best to discard the batch rather than apply it to plants, especially as a foliar spray.