The best compost tea recipe

If you're a cannabis grower interested in the zero-waste movement, compost tea could be a good place to start. This is not the kind of tea that you pour into a mug and sip. Compost tea is an organic mix of active nutrients and microorganisms steeped in aerated water. The brew packs a nutritional powerhouse for soil, roots, and leaves, introducing healthy fungal colonies (think of how probiotics benefit the digestive system) and beneficial bacteria to cannabis plants. The results are a boost in plant growth and protection from disease.

Benefits of compost tea

Though not all growers agree on whether compost tea is any more effective than ordinary compost, some cultivators have pinpointed these potential benefits:

  • Reducing the presence of weeds and pests, which consequently helps cannabis plants fend off diseases such as blight. Compost tea may shield marijuana from pathogens that could harm or even kill the plant.
  • Infusing the cannabis plant with a strong dose of nutrients, which can potentially increase plant size due to a strengthened immune system from a diversity of trace minerals.
  • Eliminating the need for chemical fertilizers that ultimately harm the soil and the environment when contaminated water leads to runoff and seeps into public water supplies. With compost tea, you are creating something 100% organic, which facilitates a thriving and self-sustaining ecosystem.
  • Maximizing water retention in the soil, meaning less wasted water.
  • Improving the overall health of the plant with a beneficial cocktail of fungi, bacteria, protozoa, and nematodes of multiple species.
marijuana plants
Some cultivators have pinpointed potential benefits of compost tea.
Photo by: Gina Coleman/Weedmaps

How long does it take to make compost tea?

Making compost tea is a fast process that lasts between 24 and 36 hours. A slightly longer brew will increase the amount of beneficial microbes, but you should not brew the tea for longer than three days. Doing so will cause the microbes to die out for lack of food supply. One benchmark to know if the brew is fresh and effective is that it will emit an earthy fragrance. Some gardeners claim that compost tea will stay fresh in the refrigerator for up to 30 days, but there is no reason to keep it on hand this long if you're ready to apply the treatment.

Apply compost tea on sunny mornings when the plant stoma are most open to receiving and absorbing the mixture. A rule of thumb is to do it when dew conditions are favorable, so if you don't have time to apply the tea early in the morning, do it at dusk.

How do you make compost tea to enhance your cannabis harvest? Here is an easy compost tea recipe, complete with all the necessary steps and ingredients.

What is the best compost tea recipe?

To whip up the best compost tea to strengthen your cannabis plants and make them more resilient, you'll need five main ingredients:

  • Compost: The first and most important ingredient is compost with a rich biome of nutrients and microorganisms. The more developed the compost's fungal colonies, the stronger the compost tea will be. Organic compost from local sources provides the best foundation for this recipe.
  • Kelp: This sea ingredient feeds the fungal colonies and aids in development, ultimately activating the potency of compost tea.
  • Molasses: More commonly used as an ingredient in baking, molasses feeds the helpful bacteria, encouraging them to proliferate and maximize the benefits of compost tea. For an extra infusion of potency, try blackstrap molasses, which is saltier and more bitter than the ordinary kind, making it better for brewing compost.
  • Worm Castings: Though not the most appetizing ingredient, worm castings are dense in easily absorbed nutrients and introduce a host of microorganisms to the tea.
  • Fish Hydrolysate: Like kelp, fish hydrolysate feeds fungi, but it also contains nitrogen and chitin, the latter of which serves as an immune booster to marijuana plants.

Once you've gathered these ingredients, you'll need a few supplies before the tea brewing begins.

What you need to make compost tea

This simple compost tea recipe doesn't require many supplies in addition to the main ingredients. You'll just need:

  • Non-chlorinated water. It can be tap water that sits for 24 hours or, for a really organic experience, rainwater.
  • 5-gallon bucket, though larger gardens may need a larger size.
  • Watering can or spritzer.

In addition, if you would like to aerate the compost, which is recommended, you will need:

  • Air pump.
  • Aquarium bubbler.
  • 400-micron mesh bag or breathable fabric, such as pantyhose or any porous cloth.

The aquarium bubbler, kelp, and fish hydrolysate can all be purchased at a fish or aquarium supply store.

Steps to making compost tea

The three steps to making compost tea are straightforward:

  • Build the brewer: Place the aquarium bubbler in the bottom of the bucket and use plastic tubing to attach it to the air pump outside the bucket. Fill the bucket with non-chlorinated water.
  • Fill the teabag (aka the mesh bag):  Remove any worms from the compost before you proceed with this step. Then, pour the tea ingredients into the mesh bag. 
  • Brew the tea: Carve out at least a 24-hour period to let the pump run continuously and brew the tea. Be prepared to apply the compost tea to the soil as soon as possible, preferably within 36 hours of adding the bag to the brewer.

There is an optional fourth step. You can supplement the compost tea with items in addition to the kelp, molasses, and castings. Try a biologically active product such as Actinovate along with supplemental food for fungi and bacteria, if desired.

Once the compost tea has brewed, apply it to the soil. You can also spray some of the mixture onto the leaves for a more thorough treatment. This usage varies from plain compost, which is applied only to the soil and doesn't directly reach every part of the plant. Foliar spraying is one benefit of compost tea, offering a more well-rounded treatment than might otherwise be possible.

Can you burn your plants with compost tea?

It is possible to burn plants with compost tea, especially if you are using a compost high in nitrogen. Manure-based composts tend to contain higher levels of nitrogen, so be sparing as you treat the soil if you are using this type and don't spray it on the leaves. Otherwise, you can be more liberal in your treatment of the soil, especially since compost tea loses much of its potency within a few hours of brewing and long-term storage is not feasible. 

Bottom line on compost tea

Compost tea is relatively easy and inexpensive to make. But it has a very short shelf-life and needs to be applied to the soil immediately to enrich the health of cannabis plants.

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The information contained in this site is provided for informational purposes only, and should not be construed as medical or legal advice. This page was last updated on September 8, 2020.