How to Make Actively Aerated Compost Tea

Eventually the gardening world tries a new technology in pursuit of bigger, better, and healthier plants. A trend that started several years ago and continues to grow is compost tea. These “home brews” of live, oxygenated soups brimming with microbes contribute significantly to the heath of soil and plants whenever they are used. Compost tea helps healthy plants resist disease and contribute to the overall well-being of the surrounding soils, plants and even the local ecological health of the surrounding garden, yard, or farm. Compost teas are scalable from small gardens to fields and farms. This article is an excerpt from Eco-Yards, written by Laureen Rama and Caron Wenzel.

Spreading good compost over your yard is the best thing you can do for your yard. But it can be time-consuming, expensive, and sometimes impractical. Enter actively aerated compost tea—the quickest and least expensive way to add soil micro-organisms to your yard. And it is about the only way to add microbes to the leaf surfaces of your plants. (Spraying compost tea has even helped some gardeners bring diseased trees back to health.) Regular applications of actively aerated compost tea will keep the microbe levels and diversity high in the soil and on your plant leaves.

Actively aerated compost tea is made by adding quality compost to water and heavily aerating it (blowing air into it) with a pump for at least 24 hours. This process fosters an explosion of microbe reproduction, creating a rich soup of micro-organisms to spray on your plants and soil. Foods for the microbes, such as humic acid and kelp, can be added to the tea while it’s being brewed.

There’s Nothing Like a Nice Cuppa Tea

Many of my clients have commented that their trees seemed richer and fuller and had fewer diseased leaves after compost tea spraying. Clients have also commented that their plants are healthier and grow larger, their yards have fewer weeds, and their lawns need less watering.

You may have heard of compost tea made by putting a bag full of compost into a rain barrel or a bucket and letting it sit. This tea does have ample nutrients, but it won’t have the microbes—most cannot live without oxygen. The liquid that may run out of your compost bin (leachate) is also rich in nutrients, but not in microbes. Only actively aerated compost tea has beneficial soil micro-organisms.

History of Actively Aerated Compost Tea

Forms of compost tea have been around since the beginning of agriculture. In the late 1970s, some Americans started experimenting with active aeration. The story goes that scientist Elaine Ingham’s neighbor in Oregon made actively aerated compost tea, and it worked magic on his roses. Dr. Ingham began to study it in 1990. Her studies and interest grew, and she is now one of the main proponents of actively aerated compost tea through her international network of Soil Foodweb Labs, whose research is mainly directed towards the use of actively aerated compost tea on agricultural crops.

Making Your Own

You can make actively aerated compost tea for your own yard. You just need some good compost and a compost tea brewer. A 5-gallon (20 liter) brewer will easily make enough tea for the average urban yard. Ideally you can use compost made from your own yard waste because you will be increasing the micro-organisms that are best adapted to your local climate and eco-system. If you don’t make your own compost, obtain good quality compost that’s made locally. Good compost has a wide diversity and high count of microbes. Best is one that has a woody component to promote fungal growth. Your tea will only be as rich in microbes as the compost used to make it.

Compost Stew

I mix a few different composts for my tea: my own worm compost, yard waste compost, and some local compost made from horse barn manure and wood chips.

Recipe for a 20 Liter (5 Gallon) Batch of Tea

1 kilogram (2 pounds) of compost (use a measuring jug: 1 L or 1 qt of volume is about a kilo or 2 lb)

To feed the microbes, add:

60 mL (2 oz or ¼ c) fulvic or humic acid

10 mL (2 tsp) yucca extract

30 mL (1 oz or 2 tbsp) liquid kelp (or a touch of kelp meal)

30 mL (1 oz or 2 tbsp) fish hydrolysate

These additives, and hydrogen peroxide to clean your equipment, are usually available in small quantities at hydroponic garden stores. They can order in some of the other additives if they don’t have them (e.g., yucca). Large quantities of these additives are available from online sources. The additives are food for the micro-organisms in the tea brewing process and once they are sprayed on your yard. You do not need all these additives, they just make for a richer, healthier soup of microbes. Do not add molasses, as recommended by some authors. It creates a brew that is too bacterial.

Preparing Your Compost for the Tea

To promote the growth of fungi, protozoa, and nematodes, you can prime your compost before brewing. Stir oats into your compost up to about 10 percent of the volume you have, so about 100 g (3 oz). Quick Quaker oats work best for me; some experts say stone cut oats are best. Add enough of your liquid ingredients to bring the compost mix to about 50% moisture. Let the mix sit for four to seven days, stirring only a few times (you don’t want to break up the fungal strands).

The Compost Tea Brewer

Ready-made brewers can be found on-line. There you can also find instructions on how to make your own brewer too.

Making Compost Tea

If you are making tea with chlorinated water, remember to let it bubble with air for two to three hours, so the chlorine evaporates before adding your compost. Put your heater in now (if you need it). Don’t fill the pail of your brewer to the top; leave at least 15 cm (6 in) of space to account for bubbling and foaming.

Put your compost in a mesh bag or paint strainer and add extra ingredients (if you use them) or have leftovers from preparing your compost. Let your tea brew for 24 hours at about 20ºC (68ºF). If the mixture temperature is lower, brew a few hours more. If the liquid foams, you can add a bit of olive oil on top to keep the foam down.

Once the tea is done, take the compost out and set it aside (you can add it back to your compost pile). Leave the air pump going and take the tubing and diffusers out of the pail (so they don’t backflood with compost tea). Once the tubes are blown out, you can turn off the pump. Strain the tea through a fishnet into another clean container.

Spraying Your Tea

To spray your compost tea on your yard, you can use a small handheld sprayer found at local garden centers. Just make sure you get a big enough nozzle for fungal strands to pass through and so it doesn’t clog (at least 35 mesh). Don’t use a sprayer that has been used to spray chemicals. Some authors recommend using a concrete sprayer, which is about the same size as a garden sprayer and less likely to clog.

If you have a little sump pump (a clean one!) you can pump the tea through your garden hose on to your lawn, trees, and shrubs. Spray the tops and bottoms of your plants’ leaves as much as you can. For spray effect, I use a little plastic hose end spreader and widen about a third of the holes with skewers. The standard recommended spray rate is 75 liters (20 gallons) of tea per acre for your soil. That is about 8 liters (2 gallons) of tea for a standard city-sized yard. If you are spraying the leaves of shrubs and trees too, then use 16 liters (4 gallons) or more for an urban yard. I dilute the tea with non-chlorinated water (from the rain barrel or bubbled to de-chlorinate for an hour) so I have more volume of tea to spread over my entire yard.

Whatever sprayer you use, use the least pressure possible. The microbes are alive and can get pulverized and squashed if they hit the soil or leaves too fast. If you live where ultraviolet sun radiation is strong it’s best to avoid spraying plant leaves between 10 a.m. and 3 p.m. The microbes take from 15 to 30 minutes to attach to the leaves, and UV rays may fry them before they can. This is not so important when you spray your soil, however, as microbes will burrow down into soil quickly. You can spray too while it’s raining, though the microbes may wash off the plant leaves if the rain is strong. You cannot spray too much tea; it’s all great for your yard!

Spraying once a month is optimal during the growing season and three times a growing season is enough. It’s good to spray in the spring to energize your yard and plants. Spraying in late fall will help the decomposition of organics, like leaves.

Clean Your Equipment

Cleanliness is the key to long-term success with compost tea brewing. Otherwise, nasty biology will grow on your equipment and harm the good stuff. Scrub off all the parts and soak any diffusers and tubing in hydrogen peroxide at about 8 percent strength at least overnight. Most hydrogen peroxide you buy at hydroponic stores is 35 percent, so dilute it to a quarter of that strength. Rinse everything well and allow drying.

This article is an excerpt from Eco-Yards by Laureen Rama and Caron Wenzel. Caron Wenzel is the owner of Blazing Star Inc. a native plant seed nursery and environmental consulting and education business. For more information visit Blazing-Star.com.