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Compost Teas for Healthy Soil

July 20, 2016

While many professional cannabis growers use compost as a plant nutrient, not as many brew it in water and air to make tea. But compost teas are gaining ground as a powerful additive. They jump start the soil and combat pests and soil diseases. Teas enhance the microorganisms that break down soil waste, yielding additional plant nutrients. The tea can also be sprayed directly on plants instead of liquid plant nutrients.

Enabling healthy soil is every bit as important as growing healthy plants. Soil is comprised of “good” microorganisms that sustain plants and their overall health. But it also contains “bad” microorganisms that can harm plants by starving them of crucial nutrients. These microorganisms thrive in anaerobic conditions (that is, without oxygen).

A closer look at compost tea

A variety of helpful microorganisms or microbes can be found in compost tea. These include bacteria, protozoa and fungal hyphae. The more diverse the microbes are, the healthier the plant will be. Some growers even use microscopes to examine the tea and ensure the proper amount and types of microbes. Tea-brewing kits can be purchased online, and it is expected that soon these kits will include microscopes.

Many growth contributors already exist in soil, such as worms and insects. These along with the microbes are referred to as the soil food web. A feeding cycle begins when microbes start multiplying after the roots release substances that the bacteria consume. The bacteria then fall prey to protozoa, which excrete other substances that convert into nutrients for the plant. This cycle occurs millions of times over during the plant’s life.

So, good bacteria consume bad bacteria. The helpful bacteria also compete against the harmful bacteria for nutrients and space and produce natural antibiotics that can inhibit the harmful bacteria.

The other helpful microorganisms in soil are fungal hyphae, which take the form of long strands. These special fungi serve to:

  • Retain soil moisture
  • Store nutrients
  • Act as a food source to other microbes
  • Create pathways in the soil to transport moisture and nutrients to the roots
  • Eliminate other harmful fungi
  • Decompose organic material

Compost tea machines, or brewers, introduce water and air into the plant. When cannabis growers make compost teas that are highly aerated and aerobic, they are doing their fair share to eliminate up to 75 percent of the harmful, disease-causing bacteria that could otherwise plague their precious plants.

Recipe for compost tea

Here’s a common compost tea recipe:

  1. Fill a 5-gallon bucket with filtered water, pond or rain water (anything that does not contain chlorine).
  2. Further oxygenate the water by using a bubbler. Compost tea microbes use up a lot of oxygen as they multiply, so a pond pump can work wonders.
  3. Fill a cotton bag or cheesecloth with compost and two tablespoons of black strap molasses. Do not use unfinished manure due to its existing, harmful pathogens. Instead of cheesecloth, other filters that can be used include nylon stockings, laundry bags, “aged” burlap or paint bags. Just don’t use any poly-woven materials, since the helpful fungal hyphae can get trapped in them.
  4. Brew the tea for 36 to 44 hours at 65° to 72°.

As soon as the tea is ready, water your plants and spray it directly onto leaves. However, the nutrient level within the tea will decline if left sitting around.

Substitutes for molasses include fish hydrolysate, kelp meal and humic acid—or you can mix several of them in your filter for the ultimate soil boost; for example:

  • 1 gallon water
  • ½ cup compost (or vermicompost)
  • 1-1/3 to just under 2 tablespoons molasses
  • ½ teaspoon fish hydrolysate
  • ½ tablespoon kelp meal








By Mary Kaye Eisele
Cannabis Cultivation Today articles are for informational purposes only and should not be considered legal guidance or advice on grow practices. You should contact an attorney or a qualified cultivation consultant for specific compliance and cultivation advice.

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