Seabird guano, or the feces of seabirds, has long been prized as an excellent natural fertilizer and soil amendment. However, some gardeners may wonder if it’s possible to add too much guano to their garden soil. Here we’ll explore what seabird guano is, its benefits and drawbacks as a fertilizer, and how much is too much when using it in your garden.
What is Seabird Guano?
Seabird guano refers to the feces and urine of seabirds, including gulls, albatrosses, pelicans, cormorants, and others. It forms as these birds congregate in massive colonies on islands and coastal areas and their waste accumulates in piles. Guano comes primarily from islands off the coasts of Peru, Baja California, and southern Africa. For centuries, guano has been harvested and transported to other regions to serve as an agricultural fertilizer and soil enrichment.
Fresh guano has a high concentration of nitrogen, phosphorus, and potassium – the three elements that plants need to thrive. As the guano ages, these nutrients break down further. Aged guano also contains beneficial microorganisms and organic matter that can improve soil structure and water retention. Using either fresh or aged guano provides an organic boost to garden soils and plants.
Benefits of Using Seabird Guano
Here are some of the top benefits of using seabird guano in your garden soil:
- Excellent source of nitrogen, phosphorus, and potassium for plants
- Slow release of nutrients over time
- Increases microbial life and activity in soil
- Improves soil texture and water holding capacity
- Can correct nutrient deficiencies
- Boosts plant growth and flowering
- Odor fades quickly after application
- Low incidence of weed seed contamination
- Can be used for container gardening
- Lasts longer than most chemical fertilizers
With this powerful combination of nutrients, organic matter, and soil enhancers, it’s no wonder that seabird guano has remained popular with gardeners for so long. The slow-release nutrients continue to feed plants over many weeks or months.
Potential Drawbacks of Too Much Guano
While seabird guano offers many benefits, it’s possible to go overboard. Using excessive amounts can potentially cause these issues:
- High nitrogen levels burn plant roots and leaves
- Excess phosphorus reduces plant absorption of important micronutrients
- Soil pH becomes too acidic
- Salts build up in soil
- Unpleasant ammonia odor
- Contamination of groundwater if over-applied
Thankfully, it’s easy to avoid these problems when you use guano in appropriate amounts. Read on for recommendations.
Recommended Application Rates
When applying seabird guano, it’s important to use no more than the recommended amounts. Over-application not only wastes this precious resource, but can negatively impact your plants and soil. Here are some general guidelines for optimal guano usage:
- Vegetable gardens – Apply 1-2 lbs per 100 square feet and work into the top 6 inches of soil. Reapply every 2-3 months during the growing season.
- Flower beds – Use 2-4 lbs per 100 square feet before planting and again halfway through the growing season.
- Trees & shrubs – Spread 1-2 lbs per inch of trunk diameter around the root zone, keeping it 12 inches away from trunks.
- Lawns – Topdress with 1-2 lbs per 100 square feet in early spring and fall.
- Container plants – Mix 1-2 tbsp per gallon of soil. Adjust rate depending on plant size and needs.
When using guano for the first time, start on the lower end of recommended amounts. Increase gradually on succeeding applications after observing your plants’ response. Always water thoroughly after applying to avoid burning.
Signs of Excessive Guano
Monitor your garden soil and plants carefully after applying seabird guano. Watch for these signs of over-application:
- Wilting leaves or leaf burn starting on tips and margins
- Poor seed germination
- Stunted plant growth
- Yellowing leaves
- Spindly, weak plants
- Decreased flowering and fruit set
- Ammonia or rotten egg odor from soil
- White crusting on soil surface
- Drop in soil pH below 6
If you observe these issues in your garden after using guano, leach the beds thoroughly with water to wash excess salts from the root zone. Hold off on further guano for at least 3-4 months and monitor soil pH and nitrogen levels before resuming use.
Alternative Organic Fertilizers
While seabird guano can be a wonderful organic fertilizer and soil amendment, take care not to overdo it. If trying to reduce your guano use, consider swapping in these other organic options periodically:
- Compost – Nourishes soil food web and provides slow-release nutrients.
- Worm castings – Rich in nutrients and enhances soil texture.
- Alfalfa meal – Moderate nitrogen fertilizer that lasts 8-10 weeks.
- Fish emulsion – Provides a quick nitrogen boost and micronutrients.
- Kelp meal – Supplies potassium, micronutrients, and plant growth enhancers.
- Bone meal – Long-lasting phosphorus fertilizer derived from animal bones.
- Cottonseed meal – Vegan alternative to bone meal, provides phosphorus.
- Rock phosphate – Direct mineral source of phosphorus.
Varying your organic fertilizers is a smart way to avoid overloading your soil with any one nutrient. Pairing gentle organic fertilizers with periodic light applications of seabird guano can give your plants a consistent diet of nutrients without the risks of excess guano use.
How to Test Your Soil
Routine soil testing is the best way to monitor the impact of seabird guano and determine optimal application rates. Here are some simple steps for testing your garden soil:
- Use a trowel to collect soil samples from around your garden, taking samples from at least 3-5 sites. Sample down to 6 inches deep.
- Mix all samples together in a clean container to create one composite sample. Remove any rocks, leaves or debris.
- Fill a clean jar with 1 cup of the soil sample. Follow the testing lab’s directions for mailing your sample.
- Choose a standard soil test that measures pH, nitrogen, phosphorus, potassium, and salt content. Most labs can email you results within a few days.
- Compare your soil test results to your plants’ needs and adjust your guano and fertilizer applications accordingly.
- Test soil every spring and fall to monitor changes over time.
With routine soil tests, you can achieve the right nutrient balance for vibrant gardens by using just the right amount of seabird guano.
Conclusion
Seabird guano is a time-tested, natural fertilizer that provides an array of key nutrients and organic matter to enrich garden soils. However, excessive amounts can potentially burn plants and create nutrient imbalances. Follow recommended guidelines for application rates based on your garden size and types of plants. Conduct periodic soil testing to dial in the optimal levels of guano and other organic fertilizers for your unique soil ecology.
With a little care and restraint, seabird guano can be a wonderful addition to your garden. Pay close attention to your plants and soil to enjoy all the benefits without going overboard.