How to Make Compost Tea
Fatten up your perennials with a cup of tea—compost tea, that is.
Natural and nutritious, compost tea not only provides beneficial microorganisms for healthy plants and soil but also helps prevent disease. For best results, experts recommend an aerated brew (those microorganisms need oxygen to thrive). Brewing kits are available but you can easily make your own. Compost tea doesn’t store well, so make small batches as needed.
To brew 11 to 15 liters of tea, you’ll need:
- Chlorine-free water*
- A 5-gallon/19-litre bucket
- A medium aquarium pump (rated for a 50-gallon/190-litre aquarium) or small pond pump
- Plastic tubing that fits the pump
- Good quality compost (homemade or purchased)
- A paint strainer bag or mesh laundry bag
- Two sturdy sticks
- Unsulfured molasses (optional, available at grocery stores)
Tea Compost Step By Step:
1/ Set up your brewer in a shady spot, near a power outlet. Run the plastic tube from the pump down into the bottom of the bucket, center it, and weigh it down with a stone or small brick. Some people like to use a gang valve with several tubes fitted with aquarium air stones that break up the bubbles. That is an option but not vital. The key is getting lots of oxygen into the tea.
2/ Put 454 to 680
grams of compost in the bag and tie the top. (You can also put
the compost lose in the bucket and strain the tea afterward.)
Suspend the bag from one stick laid across the top of the bucket
and add water to within 7 centimeters of the rim. Turn on the pump
and adjust the flow so the water is bubbling as if it were at a
vigorous boil. With the second stick, stir in 30 ml of molasses to
feed the microorganisms, but don’t overdo it, especially in hot
weather. Let the mix bubble for at least 8 hours and no longer than
3/ Remove the bag and put the used compost on the garden or compost pile. The remaining tea should have a yeasty, earthy smell. If it really stinks, it means the microorganisms are dead. Don’t use it—throw it back on the compost pile. Apply the tea immediately, pouring 250 ml or so around the base of each plant and/or spraying it on the leaves, which helps to prevent problems like powdery mildew. Clean the equipment with a stiff brush after brewing each batch.
Know you the Magic of Compost Tea
Gardeners have been making compost and manure tea for many years — probably even for many centuries. Compost tea is easier to apply than dry compost and it’s also a good way to make a small amount of compost go much further. Brewing methods are typically very low-tech: Put some compost in a bucket with water, let it sit for a few days, and then apply.
Elaine Ingham and her team are developing crop-specific compost teas that can be used on a commercial scale. Soil biologist Dr. Elaine Ingham has spent the past 15 years studying compost and especially compost tea. She has devoted her professional career to learning about the complex web of bacteria, fungi, protozoa, nematodes, microarthropods, earthworms, and other soil critters that work together to feed plants, fight pathogens and pests, and improve soil texture.
Dr. Ingham refers to this web of soil life as the “soil food web.” The research being conducted by her company, Soil Foodweb Inc., is yielding some fascinating discoveries.
Here are some of the Highlights:
For best results, compost and compost tea should be produced in an oxygen-rich, aerobic environment. This ensures that the finished product will be rich in nutrients and beneficial organisms. When compost (or compost tea) is made in anaerobic conditions, nutrients are lost to the atmosphere(which is why anaerobic compost stinks). The end product of anaerobic decomposition may also contain alcohol, phenols, and organic acids that are toxic to plant tissues.
The most productive soils in the world are those that contain the most organic matter. This wealth of organic matter can be used by beneficial bacteria, fungi, protozoa, nematodes, and microarthropods to build soil structure and feed plants. Productive soils always contain an abundance of beneficial bacteria, but the world’s most productive soils also contain a rich diversity of fungi — 1,000 times more fungal biomass than bacterial biomass.
The soil food web that’s ideal for growing a lawn is different from the soil food web that’s right for vegetables or shrubs. Dr. Ingham has found that most flowers and vegetables grow best in soils that are dominated by bacteria rather than fungi. To produce tea with a high level of beneficial bacteria, you need to start with compost that’s been made with about 45% green materials, 30% woody, and 25% high-nitrogen materials.
Effect on Diseases is Questionable
The most promising reports on compost tea come from its use in leaves to suppress diseases, especially dusty mold and gray mold (perhaps because the former is quite superficial and the second is a weak pathogen). Theoretically, “good insects” — tea microorganisms — sprayed on plant leaves could move or oppose “bad insects” — microorganisms that cause disease. Before you start using compost tea per gallon, keep in mind that most of the statements made about this liquid were anecdotal and even then inconsistent. The positive results of scientific studies have been few and, again, lack significant results for gardeners.
Compost Tea Used on Lawn
This Oregon lawn was sprayed in June, and by August, the benefits of compost tea are clear. Compost tea has proven to be valuable as a foliar spray as well as a soil drench. When leaf surfaces are coated with a layer of beneficial bacteria and fungi, “bad” bacteria and fungi are overcome and are prevented from infecting the leaves. Coating leaf surfaces with compost tea increase the biological activity on the leaf surface, which also lengthens the time plant stomates are open. This increases the opportunity for nutrient uptake, which improves growth and boosts yields.
Dr. Ingham’s organization, Soil Foodweb, Inc., has a commercial lab that will test compost and compost tea to determine the numbers, types, and activities of each important group of microbes. They can test for active bacterial biomass, total bacterial biomass, active fungal biomass, total fungal biomass, protozoan numbers, nematode numbers and community structure, and mycorrhizal root colonization.
In an aerobic environment, the microbes in compost tea will multiply exponentially.
The foam should start appearing on the surface after just 12 hours. With adequate aeration, compost tea will reach its “richest” state (most biologically active) in just 24 hours. Circulating the water and maintaining a high level of dissolved oxygen is important. Dissolved oxygen levels should be above 6.0 parts per million. Gentle agitation of the “teabag” (which contains the compost) is necessary to release the multiplying fungi into the tea solution.
Dr. Ingham’s soil research is attracting more and more attention each year. She and her team are now working in Africa, Central America, Australia, Holland, and almost every state in the U.S., devising crop-specific compost teas to improve a wide range of difficult soil conditions.