Wednesday, October 27, 2010

Building a compost tea brewer

Over the past few weeks I have been working on putting together a compost tea brewer. Transitioning to organic farming necessitated a shift from conventional fertilizer and amendments to organic, and it made sense to build our own brewer after looking at how much use we would get out of it, not to mention how much money we would save. First, we looked at how much tea we would need for at least 2 yearly applications, one in the fall and one in the spring. All of our acres at the recommended amount of 15 gallons per acre puts our need at around 13,000 gallons per application if we did every acre. After looking at various tank sizes we settled on a 1400 gallon tank. When a batch is brewed in this tank we end up with around 1200-1300 gallons of tea. Our spray buggy holds approximately 450 gallons, so 1 batch of tea will give us nearly enough for 3 full buggy loads. 3 buggy loads will do about 70-75 acres. So one batch of tea a day will allow us to spray every acre in about 10-12 days. There are 3 main parts to the tank: The tank itself, the air pump, and the liquid pump. The air pump agitates and aerates the tea to allow the organisms to multiply. The liquid pump is for filling the buggy after the batch is done. I put a float valve on a fitting and attached a hose to it for filling the tank. It takes several hours to fill the tank to 1200 gallons. It took many, many trips to JTI Supply (the tank and fitting company) to get the correct fittings. We decided to put the air pump above the tank on a bracket to prevent backflow. We had previously tried putting it on the ground and looping a length of hose up over the tank to prevent backflow, but the head pressure in the tank was too great, and water flowed back into the pump. Next we tried a check valve between the air pump and the fitting on the bottom of the tank, but the check valve inhibited the air flow too much. When we put the air pump above the tank and turned it on with the tank full, it worked for about 2 hours until the air pump couldn't sustain enough air pressure to keep the tank agitated. Turns out the air pump can only perform with less than 65 inches of water. The tank, when full, is about 75 inches high. Because of this I tried putting another opening in the side to allow the air in. This worked but we determined that the agitation wasn't sufficient on the other side and the bottom of the tank. Ultimately we decided to put less water in the tank and keep the air coming in through the bottom fitting. This will also help prevent a layer of anaerobic organisms forming on the bottom of the tank, which could degrade the quality of the tea. I purchased a bag for the tea from Earthfort, a local company specializing in compost tea. The bag hangs down from a clasp on the underside of the lid, keeping it suspended in the middle of the tank. I used quick release fittings on all the connections to make cleaning easier, as biofilm on the inside of the tank, hoses, and fittings can harm the beneficial organisms in the tea. I started brewing the first batch of tea yesterday. I used 25 pounds of solid compost. About half is from Harry MacCormack at Sunbow Farm, and half is from Shepard Smith at Soilsmith Services. I also used about 28.4 pounds of 5-2-4 Organobloom as food for the tea. This is a very basic recipe that will probably need significant tweaking to get right. I'll take a sample in to Soil Foodweb for testing today when the tea is done brewing. If the results are acceptable we can start spraying tomorrow, although I'm sure I'll need to make some adjustments to the recipe to get it right. Big thanks to Joe Richard at JTI Supply for all the materials, Kevin at Earthfort for all the advice, Harry MacCormack at Sunbow Farm for the compost and great tips, and also Shepard Smith at Soilsmith Services for the compost.


  1. how did you manage not to kill all your beneficial bacteria while pumping through your pump while filling the buggy

  2. Some pumps are considered safe so long as not being used to circulate the water. Tank that size should have a diffuser, I'd say at least three, to have enough ppm of o2