Gardeners know that compost works wonders by nourishing soil and plants. Compost improves soil structure, helping it drain well, yet still hold adequate moisture for plants. It makes nutrients more available to plants; adds important microbes to the soil; and improves the workability of soil. But compost can be heavy and bulky to transport and spread. Compost tea offers the benefits of compost in a lighter-weight package. It's a liquid version of compost, making it easier to apply to plants and soil. Plus, nutrients are more readily available.
The traditional method of making compost tea uses water to extract nutrients from the compost. The technique can be traced as far back as 4,000 years ago in ancient Egypt. It's very simple: Suspend a burlap sack filled with compost in a bucket or barrel of water and stir occasionally. The longer the compost is left to steep in the barrel or bucket or the more compost you use in relation to water, the more concentrated the liquid. This produces an extract of the compost.
Brewing compost tea is a more active process. By adding a food source, such as molasses, and adding more air to the mixture, you not only extract nutrients from the compost, but also grow a diverse population of beneficial soil microbes within 1 to 2 days. Adding the microbe-rich liquid to your soil boosts the number of 'good guys' and provides many benefits, such as increasing the uptake of nutrients and protecting plants from disease.
To make a simple compost extract, add 1 gallon of finished compost to a 5-gallon bucket. Fill the bucket to within 6 inches of the rim with water and stir it occasionally. After 3 to 7 days, strain the liquid through cheesecloth into another bucket, and use straight or diluted when to water your plants.
Commercial compost tea brewing systems make this process easy by supplying all the compost, equipment, and instructions you'll need. However, you can brew your tea with components you purchase at a pet supply store or hobby shop. It all starts with good, healthy, finished compost. You can use your own compost if you make sure your pile heats up to 140oF to kill harmful pathogens and weed seeds, or you can purchase commercially made compost.
Here's how to make a home brewed compost tea:
Add 1 gallon of compost to a 5-gallon bucket. Next, add air and food to the bucket. Attach air tubes to an aquarium pump and dangle it in the compost, keeping the pump outside the bucket.
Add 1 ounce of molasses to the compost, fill the bucket with water, and stir. Turn on the pump and let the mixture percolate for 1 to 2 days.
After brewing, strain the tea through cheesecloth, pouring the mixture into another bucket. For best results, use the tea soon after making it - aerobic microbes will die within 12 hours without the benefit of aeration and a food source.
Whether you make compost extract or compost tea, it should smell sweet and earthy. If it has a foul smell, then it may contain harmful microbes, and you shouldn't use it on your plants. Even better, to be sure your brew is free from pathogens, have your compost tested at one of the national labs that offer this service.
You can use a watering can or a garden sprayer to apply compost tea. If you're using a sprayer, filter the tea a second time through a cloth mesh or cheesecloth-like bag to strain out any pieces of organic matter.
Clean out your hand-held pump sprayer and fill with an appropriate mixture of tea. The rates of application will vary depending on your gardening situation. On poor soil it should be used straight, while on fertile soil it should be diluted - one part tea to 10 parts water. Apply it every two weeks.