When you think of tea, you’re probably not thinking about it having anything to do with compost. But while compost tea may not sound like a very appetizing drink, plants sure do love it.
What is compost tea? Compost tea is poorly named, in my opinion. This is not your grandma’s stagnant, water-soaked manure tea, and you don’t steep something in boiled water to make it either. Compost tea is made by moving microorganisms from compost into continually oxygenated (aerated) water and then giving them food to help them multiply. This aerated concoction is applied as a foliar spray or soil-drench to plants. Quite simply, it is homemade liquid gold.
What does it do? When applied to leaf surfaces, the microorganisms in compost tea act as a bandage and prevent plant pathogens from infecting plant tissues. When compost tea is applied as a soil-drench, the microbes cycle nutrients and make them available to plants. The benefits of applying compost tea include increased fruit and vegetable yields, increased disease and pest resistance, natural soil aeration and increased water retention capacity in the root zone. Plus, it’s natural, cost-effective and easy to make.
Different plants may need different types of tea, depending on whether the plant roots prefer to be dominated by bacteria or fungus (the good bacteria and good fungus, not the bad guys). Most veggies and grasses prefer bacteria-dominated tea while trees prefer fungus-dominated tea. If you want a fungal-dominated tea, then you need to start with a fungal-dominated compost source, such as worm castings, and use fungal-feeding ingredients, such as fish hydrolysate, humate and oatmeal. Most commercial bagged composts are bacterial-dominated except for a few. Ask your local independent garden center for help choosing which kind of compost to make tea with. Lucky for you, Mother Nature is very forgiving and adaptable. If in doubt, make a batch of compost tea and let nature happen.
How can I make my own compost tea? Making your own compost tea is simple using a 5-gallon bucket. All it takes is premium compost to inoculate the tea with microbes, an air pump, tubing, aquarium air stones and food for your microbes so they can multiply. You’ll want to start with a premium compost or vermicompost (worm castings) that is preferably made locally. Lastly, you’ll also need a way to strain the tea if you’re going to be spraying it on the leaves—paint strainers are inexpensive and work well. Avoid using anything too fine or you’ll filter out the microbes and defeat the whole purpose.
Food for your microbes can include liquid seaweed or kelp meal, unsulfured molasses or other simple sugar sources, fish hydrolysate, fish emulsion, ground oatmeal, humic acid or humate fertilizers and soybean meal. The meals also create more surface area, allowing microbes to attach and grow.
When making compost tea, water oxygenation is crucial. Use an air pump that can supply enough dissolved oxygen to create an aerobic compost tea. If the tea becomes anaerobic (lacking oxygen), you’ll be growing nasty microbes that can make you sick. Most aquarium pumps don’t produce enough air to use in a container larger than 1 gallon. Invest in an air pump that can supply enough oxygen (these range in cost from $35 to $50), is at least 20 watts and has an output of 45 liters per minute.
Then, use tubing and aquarium stones (more than one means more oxygen) that are weighted down so they sit on the bottom of the bucket without floating. Add the ingredients (see my recipe below) and brew in a shady location for 12 to 24 hours. It’s very important that you don’t brew for longer than 24 hours. You can add more water and brew for a longer period if you use a portion of the tea, but never add more food during the brewing process. If you accidentally allow the tea to go too long or sit too long after the aeration gets cut off, do not apply this to your plants. I like to pour it on fire ant mounds (the microbes help to destroy the ant colony) or dispose of it away from desirable plants.
Once the tea is brewed, use it as a soil-drench around the root zones of your plants or spray it directly onto the leaf surface—covering the top and bottom of the leaves. Spraying in early morning or late evening when temperatures are mild is best. I prefer to apply the tea undiluted as this has the most concentration of microbes. Apply the tea as often as you like—there is no prescribed timeline and it’s not possible to overapply it. I use compost tea a minimum of three to four times per growing season.
By Jessica Robertson • Illustration by Bambi Edlund