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How To Harvest Worm Castings

Written by Tumbleweed Admin

Harvesting Castings from The Cube
One of the many benefits of a tiered worm farm is the ability to harvest an entire tray of fine castings at once. Castings are created when food scraps are ground into fine particles in a worm’s gizzard, they are then digested by the rest of their bodies which eventually exit as castings or worm poo after a couple of days later. These casting contain valuable micro and macro nutrients which are essential for plants to grow strong and healthy. This article will go over when, where and how to empty an entire tray of castings to your garden/ back yard.
For a tray to be completely ready to harvest, here are the things to be on the lookout for:
  • Your worm farm should have a bottom (home tray) and a top tray
  • The top tray must have been added roughly 4 months ago
  • When inspecting the bottom tray, you can’t see any visible food scraps
  • The colour is a very dark chocolate brown, and is the consistency of fine mud.
  • The contents in your top tray must be about 1” below the lip of the tray
Harvesting worm castings
Picture: An example of what mature castings should look like in the bottom tray of a worm farm before harvesting.
If you’ve ticked all the boxes above, then it’s sure to say you are ready to harvest. One last thing to consider before emptying entire tray of castings, is to briefly touch on how densely packed in rich nutrients that casting are, and more specifically how they will benefit the soil.
  • Water retention: Castings retain a high volume of water when in your worm farm, this will continue when added to soil. Have you ever noticed that if you water a pot plant, water will run to the sides, rather than soak – adding castings will stop this from happening.
  • Micro and Macro nutrients which are essential for a plant to develop and grow evenly.
  • Things that you will visually notice an improvement on in your plants: leaves will develop properly; they won’t have any brown spotting which is a sign of iron deficiency.

There are quite a few scenarios in which you can add an entire tray of castings to. The general rule of thumb for castings to soil ratio, is that for every handful of castings added, you need 4 handfuls of soil (1:4). Here are a few situations in which you can add an entire tray to:
  • Raised garden bed with minimum dimensions of 1m x 2m or 3’x 6.5’
  • Lawn area, sprinkled on top
  • Side garden beds
  • Hedges
a fence and plants in a yard
Picture: An overgrown side garden with the dimensions of roughly 1m deep x 3m in length is where the tray will be emptied.

The last step just before emptying the tray is to separate the worms from the castings. Composting Worms prefer to munch on kitchen scraps, so it’s best to pick out as many and placing back in your worm farm before tipping the tray out. There are two preferred methods to do this, which are; light/ spiral method or sifting method – click the links to check out which one suits you.

a person holding a metal bin with dirt and shovel

Picture: The sifting method can be used with any tray/ drawer that has holes smaller than 1.5cm in diameter. 

dirt soil on the ground

          Picture: Worm castings straight after separating from worms 
After you’ve added your tray to the garden, it’s a good idea to lightly fold the castings in with the soil with a pitchfork. And ta-da you’ve emptied an entire tray of nutrient rich soil for your garden, jam packed with organic plant food. 
Tip: Don’t empty all the castings to your garden, save a few handfuls - These mature castings will act as a bedding block for worms in your new top tray. The worms will feel at home in these castings, it will also encourage worms venture up from their new home tray too much on your food scraps.


a small purple flowered plant in a garden

Picture: Flowering Tibouchina tree 1 week after planting 

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