Worm Composting Bin Moisture Maintenance

Worm Composting Bin Moisture Maintenance

If you’ve ever walked down a sidewalk on a rainy spring day, you understand that worms don’t survive very well when there’s too much moisture in their environment: they will drown. Worms breathe through their entire outer bodies, and too much water can prevent adequate flow of oxygen.

However, if a worm’s environment gets too dry, the worm can’t breathe either. Worms require their mucous-coating for proper breathing, and a dry environment can cause the worms’ bodies to dry out.

Maintaining the correct moisture levels for your worms enables them to breathe easier and find food. The right amount of moisture also enables worms to travel through composting material with ease, encourages worms to reproduce, and helps to maintain their overall health.

How to Check Bin Moisture

The “squeeze test” is good for a quick estimate of the moisture content of your bin, but a moisture meter is recommended for more precise regular testing.

The squeeze test is done by taking the composted material / bedding mixture and squeezing it tightly in your hand. You can tell the bin is too wet if more than one or two water droplets ring out when the compostable material is squeezed.

The compostable material will also clump together if it is too wet, or it will feel sandy, dusty, and you might hear organic materials crumble under your fingers if it is too dry. Imagine ringing out a washcloth: the residual moisture of once-wet, wrung-out fabric is the same moisture that is ideal for worm bins.

A worm compost moisture meter is best for regular testing as it gives you a precise measurement of the moisture in your bin, alerting you when things in the bin are going haywire. The measurement they offer helps you figure out exactly what corrections need to be made in order to keep your worms in tip-top shape. Moisture meters are particularly helpful during seasonal shifts in climate or in geographic regions where outdoor conditions are particularly tumultuous.

Once the meter is inserted into the worm bed, it will indicate whether the habitat is dry, moist, or wet. Consider checking your compostable material in several different places to get an accurate moisture reading: depending on where food has been composting, moisture levels might be different throughout the bin. Try to mix and disperse materials evenly to mix and disperse moisture.

How Moist is Moist Enough?

The sweet spot (where moisture levels should be): should typically be somewhere between fifty and seventy percent moist. The sweet spot for moisture is typically whatever level of humidity you must keep your worm habitat in order to produce the healthiest, happiest worms. You will know when you’ve reached the sweet spot when your worms are reproducing, eating heartily, and look healthy.

Too Wet and Too Dry: What Causes Moisture Change

Most importantly, consider what type of material you are putting into your bin. Keep a fifty-fifty balance between “greens” and “browns.” “Greens” include materials such as vegetables and fruits, and “browns” include materials that we would consider high in fiber; for example, peanut shells, shredded paper, and shredded cardboard.

Moisture rich food includes high water content fruits, such as strawberries and watermelon. Both these fruits contain about ninety-two percent water per volume.

Next highest water-content fruits:

  • grapefruit
  • cantaloupe
  • peaches
  • pineapple
  • cranberries
  • oranges
  • raspberries
  • apricots
  • blueberries
  • plums
  • apples
  • pears

High water content vegetables include:cucumbers and lettuce, which average about ninety-six percent water. Vegetables with comparable high moisture content include:

  • zucchinis
  • radishes
  • celery
  • tomatoes
  • green cabbage

It is optimal to regulate moisture in your bin by considering the water content of the food you are adding to it rather than adding water when your bin seems dry because moisture rich food adds the essential minerals and vitamins that spray bottles lack. Adding compostable, high water compost scraps rather than spraying water in your bin to raise moisture also helps keep water from pooling at the bottom and prevents improper draining, because the moisture from the foods is released as it composts.  It is important to control drainage. Do not let water accumulate at the bottom of your worm bin.

Handling Worm Bin Moisture Issues

Bin too wet

Too much moisture can hinder the oxygen from adequately flowing through your worm bin, making it difficult for your worms to breathe. If your worm bin is too wet, stop adding or limit your addition of high-moisture food. Add some dry shredded paper, coir, or peat moss to your bin.

Adding a couple handfuls of newly prepared, fresh, dry bedding will help soak up much of the moisture. Make sure to mix dry materials in, distributing the dry bedding to moist areas as needed.

Be warned: there may be a foul smell if the bin is too moist.

Bin too dry

If your worm bin is slightly dry, place a layer of moist full sheets of newspaper over your worms’ food and bedding mixture. Re-dampen the moist newspaper cover with a spray bottle as needed and let your worms snack on some high-moisture foods.

If conditions in your bin are very dry, you can add a little bit of water to the feeding tray. Use a misting spray bottle for this, as it is easy to accidentally overwater your bin when you try to apply water directly.

The water you are adding should slowly trickle down to the lower trays. Pay attention to the progress of the moisture as you add the water to your worm bin. Note how the additional water is changing the moisture of the bedding and adjust accordingly.

Additional Considerations

Pay attention to changing seasons and shifts in climate. For example, when summer starts warming up the earth and temperatures outside rise steadily to constant eighty-degree days, and meanwhile, your worms are exposed to direct sunlight, this could dry out your bin.

Likewise, pay close attention during rainy seasons. This is especially important if your worm bin is permanently or nearly always outdoors.

This being said, be aware of the moisture in the area you place your worm bin in regards to moisture. If it’s continually too dry, consider getting the bin out of the sunlight and into the shade (or if it’s too moist, move it into the light!). If it’s constantly too moist, consider moving it to a more well-ventilated area.

We offer a worm composting moisture meter for sale in our shop. Consider picking one up today and making sure your worms stay in the best possible health!

Article by Natalya Cowilich

Readers Comments (7)

  1. thank you very much for your articles! it males my day know in that little effort I’m the beginning males a big difference in the long run!

    • Welcome, Svetla!
      We at The Squirm Firm are dedicated to educating, inspiring, and encouraging people like you to discover all the benefits of worm composting.
      Stay connected!
      Let us know if you have any questions and sign up now for our free monthly newsletter. Once a month we will deliver a useful set of tips, tricks, and tools for keeping your worm composting project going strong.

      • All the information that you post about troubles you may encounter when your “green” is truly very helpful. I have plastic lined bins and i blend up all the fruits and vegetables that i feed my lil wigglers. Yes they are very spoiled!! Recently i feed them with too much water and bedding became very soggy. So I quickly added more cardboard and a fresh layer of peat moss. All seems to be back to normal again! My best advice is… If you have several bins… If you blend up their food… Inspect one of them a day or two after you feed them to see what happening in the bottom of bin. Its a lil more work but better than buying all new worms. Thanks

  2. I live in the tropics and am having a major issue with moisture inside my bins. Because it can get so hot I keep the bins in an old concrete building out of the sun, but somehow because it is so humid water keeps condensing on the inside of the bins. I don’t want to overly disturb the worms, but it seems like every day I open the bins to find water dripping off the lids and keep mixing in shredded paper and cardboard to try and absorb the excess moisture.

    I don’t want to leave the bins uncovered though because I’m concerned other critters will go digging in them.

    One bin is the kind made from storage bins and the other is the same concept except made from 10 gallon buckets. Is there maybe a way that I could improve ventilation to reduce the excess moisture?

    • Great question! One thing to note is that if moisture is condensing on the inside of your bins, it is coming from the bedding itself. If you were to let that water run off the lid onto the ground, in time you would find your bedding gets drier. One thing you could do is use a piece of well-secured screen as your lid. That would allow for ventilation and would keep critters out. A simple sheet or two of newspaper would be enough to keep the worms in the dark and would also absorb some of the moisture. Using a drill to make holes all along the top and sides is another option that will allow for both airflow and evaporation as needed. Best of luck!

  3. Michele McBrayer June 10, 2020 @ 8:52 pm

    Is it OK to use tap water in your misting bottle?

    • Super great simple question. Thanks Michele. Tap water is treated with various chemicals that make it “clean” for drinking or cooking. But those treatments also can kill some of the beneficial bacteria we rely on in the worm bin. If you leave your tap water out overnight, it becomes dechlorinated and better for both watering plants and for hydrating your worm bin bedding. That means if you want to fill up a spray bottle and just leave it- it should be fine!


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