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How & Why to Make Worm Castings Tea

Learn how to make nutrient-rich organic worm castings tea for bigger harvests, healthier trees & pest-free gardens. Zach from Arizona Worm Farm shares his recipe.

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How to Make Worm Castings Tea: Zach's Recipe for a Pest-Free Garden

What is worm castings tea?

Worm castings tea, also known as vermicompost tea, worm compost tea, or worm casting tea, is a nutrient-rich, organic fertilizer brewed by soaking worm castings (and other ingredients), in aerated water. It’s a natural way to feed your plants and boost soil health, teeming with beneficial microbes and minerals.

How & Why to Make Worm Castings Tea

Zach from Arizona Worm Farm has spent the last five years perfecting his recipe, and now he’s sharing it with us so we can learn how to make worm castings tea at home.

How & Why to Make Worm Castings Tea: Zach’s Recipe for a Pest Free Garden

Guest post by Zach Brooks, Owner of Arizona Worm Farm

Why bother making it?

It’s a lot of trouble – so let’s start with why. Quite simply: Your vegetable yield will increase. Your trees will be healthier. Your flowers will be bug-free.

What are the benefits of worm castings tea?

There’s a lot of soil science – pure academic research and decades of field testing that backs up this basic concept: if you suspend microbes in clean water and add air, the microbes will multiply dramatically. When you then transfer that microbe-laden brew into your soils and onto your plants, the microbes thrive and do what they do almost immediately.

How to Make Worm Castings Tea: Zach's Recipe for a Pest-Free Garden

Here’s what all those microbes do:

  • Help produce thicker leaves so your plants protect themselves against frost, sunburn, and pests. 
  • Rapidly convert organic matter from the soil into food for your plants.  
  • Tell your plants there are pests present before those pests arrive, so your plant protects itself from the inside out.  
  • Extend the reach of your plant’s roots so your plants grow better with less water. 
  • Eat harmful microbes.  
  • Improve soil structure through the formation of soil aggregates. 
  • Increase soil porosity, resulting in better aeration and water retention. 
  • Stop the degradation of soil pollutants and provide pH buffering.

Convinced about the benefits of worm castings tea? Let’s talk about how to make it.

How & Why to Make Worm Castings Tea

Worm castings tea recipe development

Over the last five years, I have run more than 125 experiments where a standard recipe was compared to variations of ingredients or procedures.

We then looked for and counted microbes under a microscope.

How to Make Worm Castings Tea: Zach's Recipe for a Pest-Free Garden

Worm castings experiment findings:

  • The 27-hour brewing time increased protozoa activity.
  • Humic acid stimulated fungi activity.
  • Kelp stimulated protozoa activity.
  • Fish fertilizer stimulated fungi activity and increased nutrient content.
  • Worm castings resulted in increased fungi content.
How & Why to Make Worm Castings Tea

I am going to share our recipe and approach – although I will reiterate, that this is a bit of a bother, and you need the correct inputs to get this right. 

We sell it fresh every Saturday morning here at the Worm Farm. An easier option is to just come by a gallon or two.

Use fresh and varied inputs for the best tea

Start with as varied and healthy a collection of microbes as possible. Use your castings, fresh from your worm bin, and your compost, fresh from your piles. Use other sources of microbes like hydrated mulch that is breaking down or mushroom compost.  

Add vermicompost to make worm castings tea
Worm castings from in-bed vermicomposting bins

If you don’t have your own, buy them from a local farm where you can get fresh. The big box compost and worm castings sealed in plastic do not have much microbial life. If you come here to my farm and want inputs for your tea, tell us so we can sell you unscreened material.

How & Why to Make Worm Castings Tea
Decomposed hydrated wood chip mulch

We don’t screen any of the inputs before we use them to make our tea here. The compost and castings will have larger chunks of wood than our typical commercial product. This mostly serves to reduce microbe exposure to heat and dryness and to avoid breaking fungal hyphae strands.  

Worm castings from in-bed vermicomposting bins

The other ingredients are humic extract, kelp meal, fish hydrolysate, and Arizona Worm Farm’s BSFL Nutrient +. How many of these you use is up to you. The extra additives will improve the tea but are not essential.

How to Make Worm Castings Tea: Zach's Recipe for a Pest-Free Garden
The ingredients for worm castings tea

Gather the supplies

How & Why to Make Worm Castings Tea
  • A seven-gallon bucket (This size allows you to make 5 gallons of tea.)
  • A “tea bag” (You can add the material to the water and aerate it, but the bag makes it easier to spray and use in our gardens.)
  • A pump that can produce a “rolling boil” – bubbles that make the water look like it is boiling hard – with no heat. We recommend this home brewing kit from Compost Tea Lab. It contains a pump, a bubble snake, and a tea bag.
  • Hose end sprayer
  • Fresh worm castings
  • Unscreened compost
  • Decomposed hydrated wood chip mulch
  • Humic extract
  • Commercial kelp meal 
  • Fish hydrolysate
  • Arizona Worm Farm’s BSFL Nutrient + 
How to Make Worm Castings Tea: Zach's Recipe for a Pest-Free Garden

Zach’s Worm Casting Tea Recipe

Serving Size:
5 gallons
24-27 hours


  • 5 Gallons (19 liters) of pure well water, collected rainwater, or city water allowed to sit out overnight. *see note
  • 12 oz (340g) worm castings 
  • 4 oz (113g) of unscreened handmade compost
  • 4 oz (113g) decomposed wood chip mulch (hydrated)
  • 2 Tablespoons (30g) humic acid
  • 2 Tablespoons (30g)  kelp meal
  • 2 Tablespoons (30g) fish hydrolysate
  • 2 Tablespoons (30g)  AZWF BSFL Nutrient+


  1. Place the bubble snake in the bucket.
  2. Add 5 gallons of water to the bucket. (see temperature note below)
  3. Fill the compost tea bag with castings, compost, and mulch.
  4. Tie the tea bag to the snake.
  5. Add liquid and powdered ingredients to the bucket.
  6. Turn on the pump.
  7. Replace ingredients in the tea bag with fresh castings, compost, and mulch after 1 hour and again after 2 hours. After the 3rd hour of aeration, take the tea bag out of the bucket. (Add spent ingredients to garden beds or containers.)
  8. Continue aerating the tea for 21-24 hours, but not longer.
  9. Use tea within 2-3 hours. The microbes begin dying when you take the tea off the bubbler. After 4 hours, the numbers return to where you started. 

* A note about water: Most city water has chlorine to kill parasites, bacteria, and viruses. It kills the bad stuff but also kills the good stuff. If you only have access to city water, add water to the bucket and let it sit overnight. The chlorine will dissipate. If you are in a hurry, boiling for 15 minutes will have the same effect. Allow to cool before use.

Temperature: Keep water temperature between 60-70°F (15.5-21°C)–above 85°F-90°F (29-32°C) is too hot.

Recipe courtesy of Zach Brooks, owner of Arizona Worm Farm

Printable copy of the worm castings recipe:

How to apply worm castings tea

How & Why to Make Worm Castings Tea

There are many ways to apply tea – and they are all easy. 

As a soil drench: Pour it on the soil around your plants. Add 2 gallons of water to each gallon of tea for a soil drench. Or use it at full strength and then water the soil well.

How & Why to Make Worm Castings Tea

Foliar feed: Add it to a hose-end sprayer and spray it as a foliar feed.

How & Why to Make Worm Castings Tea
  • Strain the tea through an extra fine mesh strainer before use.
  • Put the dial on the “most product” level and fill the jar with undiluted tea.
  • Rinse the filter in the hose end sprayer frequently. The hose end sprayer should empty quickly. If it is not emptying, the filter may be clogged.
How & Why to Make Worm Castings Tea
Straining the tea and rinsing the filter will allow the tea to spray freely.

Irrigation injection system: Follow system instructions for use.

 When to apply worm castings tea

1. At the beginning of each season

  • In the fall to get your plants ready for frost.
  • In the spring for a harvest boost.
  • Just before summer to get plants ready for the heat. 
  • Use it as often as weekly; it only does good. However, more than four times a year is probably not worth the time and money.

2. When setting up new garden beds or adding fresh soil

Apply tea when you set up a new bed (to get the soil ready). For best results, apply it a week or two before you plant, and then keep the soil watered like you had plants in it.

3. When planting new trees

Using worm castings tea when you plant new trees has been shown to dramatically reduce transplant shock and help new trees establish roots.

How to Make Worm Castings Tea: Zach's Recipe for a Pest-Free Garden

4. To add microbes when fertilizing your fruit trees

Adding microbes in the form of worm castings or worm castings tea is the first of four steps to fertilizing fruit trees. Learn the additional steps in this blog post.

Arizona Worm Farm offers fresh worm castings tea most Saturdays. They also offer mobile tea sprays. See their website for availability.

How to Make Worm Castings Tea: Zach's Recipe for a Pest-Free Garden

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