It's Tea Time!

By Tad Hussey

Compost tea has become increasingly popular in the last few years as part of a grower's program. In fact, the current world record holder for giant pumpkins was grown using this technology. I'd like to take this opportunity to discuss different types of compost teas and share some of the knowledge we've gained in the industry over the past 5 years.

Let's start by looking at some of the different types of teas you can make for your plants:

Plant Tea - This is where plants are soaked directly in water for an extended period of time. Compost is not involved, and any bacteria or fungi on the surface of the plant will be extracted. May contain some soluble nutrients.

Manure Tea - Typically manure is placed in a permeable bag (burlap) into a bucket or barrel and left to soak for an (# of days) extended period of time. Compost is not involved, and will be dominated by anaerobic organisms (bacteria and ciliates). Pathogens will be present in most instances, and may burn the leaf surfaces of plants. These teas will contain some soluble nutrients, but may also contain antibiotics and growth hormones such as tetracycline, that are not broken down during the composting process.

"Put To Sleep" Tea - These teas are typically advertised as "instant" compost teas. Specific organisms are cultured or extracted from compost and then put into a dormant state. Even with hundreds of different species, it won't contain even 1% of the diversity or quantities you would find in properly made aerated compost tea. These teas may be helpful in certain instances when you wish to combat certain diseases and know the proper microbe that has been documented to prevent or suppress it (eg. trichoderma).

Compost Leachate - These teas is sometimes referred as "worm tea" as it is the liquid that leaches out of the base of worm bins or compost piles during the composting process. Leachates will consist primarily of soluble nutrients, but will contain some small amount of biology. This can serve as a good food substrate for the biology in your soil.

Compost Extract - Compost extract is where the microorganisms are stripped from the soil aggregates using water and extracted into a liquid form. This process will contain good biology for soil drenches, and can be made very quickly, as it does not require a brewing process. It does however require a large amount of compost relative to the final liquid product, and is primarily used in large commercial productions.

Non-Aerated Compost Tea - This is where compost is put into a container with water and foods are added for the microbes. The tea is then stirred occasionally or left to sit for a period of time. These teas may or may not produce beneficial results and could potentially harm your plants depending on the anaerobic organisms in your starting compost.

Aerated Compost Tea (AACT or ACT) - Similar to the tea above, this process involves adding oxygen to the tea and a food source for the biology in the compost. By creating optimal conditions for aerobic microbes, AACT allows you to multiply the biology in the starting compost by over 10,000 times. Many plant pathogens are anaerobic and prefer low to no oxygen conditions. By making sure the tea and the compost itself are well oxygenated and highly aerobic, you can potentially eliminate 75 percent of the potential plant-disease-causing bacteria and plant-toxic products.

For the past 5 years, AACT has become the standard within the organic industry in regards to compost teas. It's currently being used by golf courses, vineyards, farmers, and homeowners as a means of growing healthier plants. Here's a list of some of the benefits:

Compost tea has been shown to help in disease-suppression (pythium, phytopthera, powdery mildew, fusarium, etc.) when applied as a foliar spray and soil drench.

Helps extend root systems

Increases water and nutrient retention

Is 100% safe and natural

Creates healthier plants

Helps breakdown of toxins in the soil and on the plants

Enhances the taste of fruits and vegetables

Reduces or eliminates the need for chemical pesticides, herbicides, and fertilizers

Occupies the space around the infection sites so disease-causing organisms cannot penetrate into the tissues of the plant

Cannot be over-applied because it is completely natural and organic

These benefits are all attributed to well-made AACT. If the tea is not made properly, you will not see all of the benefits listed above. Let's take a closer look at what goes into making quality aerated compost tea.

  1. Good compost is very important! Without good biology in the compost, you really have no chance of getting high-quality tea. You can only multiply what you put into your brewer, therefore good compost that has been tested to have high numbers and a diversity of beneficial organisms is essential. A lot of science goes into making good compost, and unless you test your compost you really have no idea if what you are putting into your brewer is truly beneficial. By adjusting the type of compost you put in the brewer you can control whether your tea is going to be bacterial or fungal dominated. We use a mix of 3 different composts (Alaska humus, vermicompost, and a fungal compost comprised of woody materials) to increase the biological diversity in our teas.
  2. Food is critical for the microorganisms so that they can reproduce and grow in numbers. The goal is to maximize your output of beneficial biology without giving the bacteria and fungi too much food that they over-replicate and cause the tea to go anaerobic. It's important that dissolved oxygen levels stay above 6 mg/l during the entire brewing cycle. There are many different recipes out there, each of which will give you different biology in the end and some are much better than others. It is important to see the lab results of the recipe you use to make sure that you are indeed maximizing your final product.
  3. Oxygen! All living organisms need oxygen to survive, and your tea is no exception. If you're not getting enough oxygen in your brew, then your tea will go anaerobic and you will start brewing the "bad" organisms (pathogens such as e.coli or root feeding nematodes) that may have existed in your original compost. If your tea has enough oxygen and stays aerobic for the entire brew cycle, what you'll have at the end will be the good biology that you want for your plants.

In addition to these variables, other things to consider are elevation, temperature, brewing time, and water quality. All of these variables can have a significant impact on your final tea. With significant elevation, you may need to increase the brewing time, due to the lower oxygen content in the air. With high temperatures, where the water temps are 90 degrees or above, you'll want to shorten the brewing cycle and possibly cut back on the foods you're using. In cold temps., you'll want to increase the brewing cycle to give the organisms time to reproduce. In regards to water quality, different sources will have different mineral or chemical content, which will affect your final tea. In the case of chlorine or chloramines, these chemicals will need to be removed prior to adding the compost to the brewer.

In the next article, I'll be discussing application rates, recipes, basic pointers, and common mistakes people make when building a brewer or in making AACT.