Worm castings and its delicious tea.

by Alex Robles

Greeting my fellow cultivators, I hope everyone’s day was close to perfect.  Today I’m going to preach about all the beautiful things I love about worm castings sometimes called vermicast, worm poop or worm manure, it’s all the same thing.  I want to start by mentioning that castings are the only fertilizer I know of that has very little order and is safe to use around kids and pets as well as indoors.   The easy rule that I use for spotting quality castings is “the darker the better”, I like them to be a little darker than wet coffee grounds.  Since castings are water activated, it’s ok if I get a bag of castings and it dries out a bit.

Growers Note:  When 10% – 20% of worm castings were mixed with composted dairy, horse, chicken manure, or plant compost almost all bad odors were eliminated within eight hours.

Worm castings aren’t really compost in the sense that a “hot” method isn’t used when it’s made compared to manure/plant compost.  Castings are made inside worms which like a temperature range of 60-80 degrees F, while compost needs temps of 130 -170 degrees F.


You cannot overfeed or burn your plants NPK with worm castings because it won’t let the plant absorb more nutrients then it needs.  Instead because of the beneficial microbes that are in it, the unused nutrients will be locked away in the soil until they’re needed.  It’s also known that worm castings are a great source of NPK but the levels are about 1% for each and that seems low when compared to chemical fertilizers.  But what we have to remember when we’re talking about nutrients is that availability is what’s important.  You can have more than enough nutrients in your feeding mixture but if the plant can’t absorb them then they’ll just get washed away during watering/feeding.   All of primary and secondary nutrients found in castings are in a form that can be absorbed by the plant because of all the beneficial micro-organism that live in castings.  The same or higher rate growth and a more balanced growth is seen in gardens where castings are used without having high concentrations of chemical fertilizer in the soils or waterways.  As a matter of fact castings are pathogen free and have a huge role in cleaning up the soil that they’re put in.

Pest control

This is my favorite part of worm castings because aside from being a rich in nutrients it also has a surprise for pests.  It helps the plant produce chitinase (kite-an-ase) in its sap.  Chitin helps make up the exoskeletons of most bugs that can infest your cannabis plant.  Chitinase breaks down chitin, so when a pest nibbles on the plant it gets a spicy dose of chitinase and it decides to move on.

Disease and Fungi

Some fungus is an essential part of healthy soil, but too much will cause problems when it gets out of control.  Fungus eating protozoa and nematodes are in worm castings and using it in the soil mix will help control most fungus.  It will also provide improved plant growth with the release of extra nitrogen as the soil fungus is brought under control.  Within a few weeks, plants that had a fungus problem will show noticeable improvement.  Because of the humus in the worm castings it has the ability to fight plant diseases by taking the toxins and bacteria from the soil and allowing them to be washed away as organic waste.

Soil benefits

Worm castings help make aggregates or mineral clusters in the soil or coco coir that help against water erosion and compaction, think of aggregates for water simply as clumps of sponges.  It will also help balance the pH levels in the soil and adjust the carbon-nitrogen ratio so plants can take up nutrients easier.

When you feed a plant dry soil amendments like worm castings it will take about a week them to start to be broken down and absorbed by the plant and noticeable benefits could take as long as 10 day to two weeks.   For faster absorption, worm castings can be made into a compost tea.  Here is my simple “worm tea” recipe that I feed my plants at least once a month.

Worm Tea Recipe

Things you’ll need.

  • 5Gal bucket of water
  • 5Tbls of fish and kelp liquid fertilizer
  • 1/3 cup molasses (the sugar feeds the microbes), sometimes the you’ll find a fish/kelp fertilizer with molasses already in it.
  • 1 ½Tbls of “Recharge” (beneficial microbe soil amendment)
  •  6 ½ cups of worm castings wrapped up tight in cheese cloth or old t-shirt, like a tea bag.
  • Air stone, air hose and pump (optional)

Now let’s put it together.

  1. Add the fish/kelp fertilizer and Recharge to the 5gallons of water.
  2. Drop in the tea bag of worm castings.
  3. Hook up the air stone to the air pump and put the stone in the bucket of water, then turn it on. It’s normal for the tea to start to foam up, it’s a good sign.  The tea should be ready in about 24hrs.

If you don’t have an air stone and pump, don’t worry you can still make this tea.  You’re going to do steps 1 & 2, but you’re going let everything sit in the bucket for 2 days.  Remember to stir the bucket often.

Well we’ve reached the end of what I know about worm castings, I hope this helped.  I’ll talk to y’all next time.

Here’s a short video

Grow, Learn, Teach

Worm castings

Kelp fertilizer


air pump

air stone

air hose


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