Compost Tea: Liquid Gold Or Waste Of Time

Compost tea. Made from steeping finished compost in water, has been promoted as a great source of both nutrients and pest controlling microbes for plants. The theory is that the components of solid compost, which does contain both beneficial plant nutrients and living microbes, can be extracted into water. Much like making teas from dried herbs.

Sounds great.  Concentrated liquid compost that can be used  as a soil drench or a foliar spray on plant leaves.  Feeds and protects plants from pest and disease.

There is aerated compost tea, where the use of a pump introduces oxygen to the mix.  This is to encourage microbe growth in the brewing tea.  Typically molasses is also added to feed this growing population of microbes.

And there is non-aerated compost tea, where the compost-water mix just sits and steeps for a period of time.  Occasional stirring allowed.

In both approaches, the mix is typically allowed to steep for anywhere from 24-48 hours to allow the compost to fully release all of it’s plant beneficial components into the water.  Those beneficial components are fungal and bacterial microbes, as well as base organic nutrients.

But producing a good quality compost tea requires some time and effort.  Is it worth it?

Making Compost Tea

I have been making my own compost tea over the last couple of growing seasons.  I have a five gallon bucket that I fill with pond water into which I submerge a mesh bag filled with compost.  I add a tablespoon of molasses and a couple of aerators that used to feed off of a fish aquarium pump.  I’ve switched pumps, as you will find out about later in this post.

Why pond water?  Because you don’t want to use tap water that may contain chlorine or other chemicals that will prevent natural microbe growth.  Instead of pond water, I will sometimes fill the bucket with tap water and let it sit out overnight to allow enough time for the chemical content to dissipate into the air.

After brewing for a couple of days, I will use the resulting tea to drench the garden.  If I’m watering into the soil, I’ll use the tea as is.  If I’m spraying directly onto my growing plants, I’ll dilute it with pond or untreated water.  Concentrated compost tea can burn plants.

But again, is this effort to produce compost tea providing any more benefits than if I just spread solid compost directly in the garden?

This year I decided to do some research to see if my use of compost tea was really providing the nutritional and medicinal kick to my garden that I was hoping for.

And what I have discovered is that there is a great debate over the value of compost tea in the gardening world.

Raising plants is like raising kids for many people.  So the how-to arguments can get pretty spirited.  Let’s raise our shovels and hoses and jump right in.

Compost Tea: A Garden Elixir

Proponents of compost tea typically adhere to the gardening is less about growing healthy plants and more about about growing healthy soil concept.  Soil is more than just dirt.  Good soil is a complex, symbiotic ecosystem made up of fungal, bacterial, mammalian and invertebrate life.  This system is often referred to as the soil food web where the organisms and animals in the dirt form a circle of life.

Compost tea, by adding bacterial and fungal microbes to the mix, encourages the growth of those organisms that support the soil food web.  And a healthy soil food web ensures that plants have a ready supply of nutrients available for easy absorption.  The soil food web is a complex system of living organisms that feed off one another.  We discuss what makes up the soil food web here.  But the bottom line is that as these organisms live and die, they leave behind compounds that are critical for plant nutrition in an organic growing environment.

In addition, beneficial organisms in the soil also feed off of many plant pests.  So, they are also a key part of an organic pest control program.

Compost tea advocates maintain that aerated compost tea can also provide a booster shot of pest fighting microbes to plant foliage.  Spray the aerial parts of the plant and these microbes can help cure and prevent disease and crawly pests from ravaging plant leaves and stems.

But even the most ardent compost tea fans admit that there are some best practices you need to be aware of to get the full range of benefits from a brewed batch of tea.

  • Aeration is key.  The more the better.  The microbes in compost tea use a tremendous amount of oxygen to grow and reproduce.  I have learned that using a typical aquarium pump in a five gallon bucket just does not provide enough aeration.  This year I have purchased an inexpensive, but far more powerful, pond pump to generate the air circulation needed to support microbe population growth.
  • Annual plants, including vegetables, tend to prefer soil heavily populated by bacterial microbes.  Thus you want to use green, nitrogen rich compost such as manure or green plant material as the soaker in your compost tea.  This will produce a tea full of bacteria just ready to jump into the soil food web that your plants need.
  • Perennials, including fruit trees and bushes, prefer soil packed with fungal microbes.  So, you want to use compost tea made from carbon rich brown compost materials such as dry leaves or straw.
  • After dispensing your tea, make sure you thoroughly clean all materials used in making the compost tea to prevent the growth of harmful microorganisms.

Now let’s cross the battlefield to see what the other side of this debate has to say.

Compost Tea: Just Not Worth the Time and Effort

Those who pooh pooh the benefits of compost tea maintain that there is no authoritative literature that attests to any significant fertilizer or pest control benefits from the use of compost tea.  In fact, a 2007 study at Cornell University concluded that due to the  wide range of brewing practices, the microbial content of most compost tea is typically very low and of no real benefit when compared to the time and effort required to produce it.

And forget about bottled compost tea you see on the nursery shelves.  If these beneficial microbes require all this oxygen to live and grow, how do you think they’d still be alive after being cooped up in sealed plastic bottles?

In addition, the naysayers warn, the conditions needed to brew compost tea, are also ideal for the growth of harmful organisms such as E-coli and salmonella.  Definitely don’t want to be watering my plants with water filled with those bad boy bacteria.  But keep in mind, if there are no pathogens in the compost, there will be no pathogens in the tea.  So, to get over the bad bacteria concerns, stay away from using any type of unfinished manure when making the tea.

And, they say, rather than going through the time and expense of making compost tea, just put down quality compost.  It will provide all the benefits associated with adding nutrients and healthy microbes into the soil.  You’ll just need more of it.

And the Winner Is?

I have no clue whether compost tea really provides that much more of a soil boost than directly applying compost.  Common sense tells me that if the compost extraction process is efficient and if the molasses and aeration do serve to grow the colony of healthy microbes, then compost tea does represent a concentrated source of soil nutrition and pest control.

Regardless, if produced correctly, applying compost tea to the garden can’t hurt.  So, I don’t mind investing the time to make the stuff.  I try to follow good brewing practices to maximize my chances of getting a good, rich tea.  And I typically use it once a month or so to drench the soil and spray onto my edible plants.

Is it working?  I think so.  I’m growing soil, and any treatment that adds beneficial friends in the dirt can only help.

Where do you stand on the great compost tea debate?

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  • Frank Komitsky Jr

    Use rain water if there is no pond handy. If there is a pond, make sure that it is not contaminated.

    • jdbell60

      Frank – you are absolutely right! In the absence of a pond or rain water, you can also use tap water after leaving it out for a day or so to allow treatment chemicals to dissipate. You can speed up that process by aerating the tap water to help force the chemicals release into the air.

  • Selene Jon

    Like always, this is a very interesting article.

    • jdbell60

      Thanks Selene!