How to Ensure the Moisture Level of Worm Bin Bedding Is Right

The excess liquid that is drained from a worm farm tap is called worm farm leachate (worm juice). It's similar to worm tea.
The excess liquid that is drained from a worm farm tap is called worm farm leachate (worm juice). It’s similar to worm tea.

Worms need moisture in order to breathe oxygen through their skin. If a worms skin dries out, they will suffocate. Likewise, if the moisture level of worm bin bedding is too high, they will drown. And when conditions are too wet, it deprives oxygen that is needed to support the breakdown of foods. This results in all kinds of anaerobic activity in the worm bin and a toxic environment.

There’s always a moisture level sweet spot, where your worms are reproducing, eating happily and look healthy. However maintaining a consistent moisture level can be a challenge, especially due to changes in weather. Luckily composting worms are tolerant of a wide range of dampness (50%-90%). The ideal moisture level of worm bin bedding is about 80% moisture content.

Most of the moisture in the bin comes from the food that you add. Did you know that watermelon is 92% water? You may find our guide on what do worms eat interesting.

Too Wet

Worms don’t like too much water. Too much moisture can down your worms. If your worm bin is too wet, the worms will seek dryer conditions. And if you notice your worms are becoming pale in color or are skinny then your worm farm moisture levels are probably too high.

A wet worm bin can cause a slowdown in worm productivity. And even worse it can become a stinky mess of anaerobic activity which may spoil your entire bin. You might also see some white maggots  (soldier fly larvae) appear as they prefer sloppy conditions. The acidity in the worm bin may increase due to the anaerobic conditions. In this scenario, it is also common to see lots of fungal growth. In addition, too much moisture makes it difficult to harvest worm castings and separate the worms from it.


A wet and soggy worm farm may be the result of:

  • Adding too many foods that are high water content – It’s not rocket science to figure why they called it Watermelon. It’s 92% water!
  • Adding too much water  – You should not need to add any extra water into the worm bin. That is unless the temperature is extremely hot. There should be enough moisture supplied by the food scraps you add.
  • Insufficient bedding – Fresh bedding helps to soak up any excess moisture. If you don’t continually topped up your worm bin with fresh bedding as it disappears, any excess water will have nowhere to go.
  • Improper drainage – It’s not uncommon for the worm bin drainage holes can get clogged up with worm castings. The worm castings and bedding can also get become too compact which negatively impacts drainage and ventilation.
  • Depending on the design of your worm farm, the water from rain can sometimes get inside through the ventilation holes (if any) on the lid.


The quick solution is to add some dry paper or cardboard on top of the bedding to soak up excess moisture. You should also check the drainage of the worm bin to ensure there are no blockages. Stop adding food for a bit so the bin can dry out a bit more. And stop adding water in your worm bin if you have been doing this. There should be enough moisture provided by the food scraps you add.

The longer term solution is to add lots of bedding material such as straw and paper. And more importantly, make sure you are not over-feeding the worms as this can cause excess moisture. And be aware of the water content of foods you add into the worm bin (e.g. cucumber and lettuce are 96% water).

How to Fix Common Worm Farm Problems

You might want to check out this comprehensive “goto” guide on common worm farm problems and how to fix them.

Too Dry

Worms need moisture so that their skin can absorb oxygen and give off carbon dioxide. A mucus coating on the worms skin helps this process. If the worm bin moisture level is too try, the worms body will dry out and they will eventually suffocate. If you start seeing ants invade your worm bin, it’s probably a sign that your worm bin is too dry.


A dry worm farm may be the result of:

  • Low C:N ratio – Carbon such as newspaper and cardboard soaks up moisture. Not adding enough food will also reduce the supply of moisture.
  • Changes in weather – Hot dry weather will obviously dry out your worm bin and remove moisture from the air.


The quick solution is to add some water using a spray bottle until you have the correct moisture level.

The longer term solution is to keep a 50:50 balance between Greens and Browns. Greens include vegetables and fruits whereas Browns are higher in fiber and include carbon materials such as paper and cardboard. Always make sure you have plenty of damp bedding on top to keep the moisture in. A worm blanket also does a good job.

Moisture Content of Food

Be aware of the water content of foods that you add into the worm bin. Cantaloupe for example is 90% water.
Be aware of the water content of foods that you add into the worm bin. Cantaloupe for example is 90% water.

Aside from the list foods that you should be feeding your worms, you need to be aware of the water content of foods as well. Feeding too many high moisture foods such as zucchini and watermelon can cause a worm bin to become too moist.

Here’s a list of fruits and vegetables and their percentage of water content for reference:

Fruits Vegetables
  • 92% – Watermelon and strawberries
  • 90% – Cantaloupe
  • 97% – Pineapple, oranges and raspberries
  • 91% – Grapefruit
  • 88% – Peaches
  • 86% – Apricots
  • 85% – Blueberries
  • 84% – Apple, pear and tomatos
  • 81% – Cherries and grapes
  • 74% – Bananas
  • 96% – Iceberg lettuce
  • 95% – Cucumber, celery, zucchinis and radish
  • 93% – Green cabbage
  • 92% – Peppers, cauliflower, eggplant, red cabbage and spinach
  • 91% – Broccolli
  • 87% – Carrots
  • 79% – Green peas

For interest, worms are 90% water. In comparison, humans are about 75% water.

The Ultimate Worm Farm Guide for Beginners

Are you thinking about starting a worm farm? This guide will teach you everything you need to know about how to start a worm farm.

Checking The Moisture Level of Worm Bin

Maintaining a consistent moisture level in the worm bin can be a real challenge. The moisture level of the worm compost material is what we care about. So don’t worry if you see condensation on the lid and sides of the bin. The moisture levels throughout the win will be uniform as well. There are many factors at play inside the worm bin which influence the moisture level. This includes:

  • Temperature
  • Humidity
  • Foods
  • Bedding
  • Ventilation
  • Drainage

There are 2 methods for checking the moisture level in the worm bin:

  1. The Squeeze Test – This method provides a quick and rough estimate of the moisture level in the worm farm.  The moisture in the worm bin bedding should be as moist as a wrung-out sponge. Grab a handful of bedding and squeeze it tightly in your hand. You should see only a few drops of water. If you can’t, then your worm farm may be too dry. The material will also clump together if it is too wet, or it will feel sandy, dusty and crumbly if it is too dry.
  2. Using a Moisture Meter – For a more precise measurement of the moisture level in the worm bin, a moisture meter is recommended. The ideal moisture level of worm bin bedding is about 80% moisture content. Make sure you take the average of numerous places for a more accurate result, as the contents in the worm bin are no uniform. Sinking the probe into an area full of watermelon for example will obviously show a higher than expected reading. Likewise, insufficient watered peat moss may give the false impression that the worm farm is too dry.

Other Tips

  • You can drill some holes all along the top and sides of the bin to increase for both airflow and evaporation as needed.
  • Always remember to drain the worm farm leachate. Do not let the water accumulate at the bottom. I keep the spigot open at all times with a plastic container underneath to catch the leachate. This prevents flooding.


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