5 Tips To Keep Correct Moisture In Your Worm Bin

A possible challenge for a beginning vermicomposter to get a handle on is keeping the moisture levels in the bin at a reasonable level. Thankfully, composting worms are very tolerant of a wide range of dampness, between 50-90%.  But “wet it and forget it” is decidedly not a winning plan.  A sopping wet worm bin can cause a slowdown in worm activity and reproduction and worse yet, stinky, anaerobic conditions which may spoil your entire bin.  The following tips assume you have an indoor plastic bin (the most common, but wettest bin set up) and should help you keep clear of turning your bin into your own personal Swampland (or Sahara) in a box.

1.  Measure Moisture in Several Places

Compared with commercial systems, home vermicompost containers are not uniform in their content.  Home bins will feature shredded cardboard and paper, peat moss, coffee grounds, corn cobs, apple cores, banana peels and whatever food waste that household is producing at the time.  I’ve even seen a fellow worm nut toss old t-shirts in his worm beds, presumably for insulation.

If you use some sort of a probe to measure moisture, this presents the challenge of inconsistent readings.  Sinking the probe into an area full of watermelon chunks is sure to give you a higher-than-expected result.  Likewise, insufficiently watered peat moss may wrongly give you the impression that it’s time to water the bin.  Take the average of numerous readings to get a more accurate result.

2.  Be Aware of the Moisture Content of the Food

BREAKING: Watermelons have a lot of water! 

While you’re picking yourself off the floor, let me take the time to admit I’m often guilty of feeding my worms according to the “a little here and a little there” without much regard to what exactly I’m feeding them.  Vermicomposting is not cosmic stuff, and a consistently-fed indoor bin is likely to maintain appropriate moisture levels with very little effort on your part.  But it’s always advisable to (research water content of various organic foods) to consider your worm food choices and how they might affect worm bin moisture.

3.  Pay Attention to the Weather

This is a no-brainier for outside bins exposed to the elements, but for indoor systems, ambient humidity still plays a large part in maintaining proper water levels.  (Ask me how I killed a bin of worms in a very dry winter recently). 

If you’re like me, and your spouse or roommates demand you keep your buddies out of sight, you’ll probably store your bin in the basement if you have one which, during periods of rainfall, will be pretty damp.  This is a good thing!  But if you have a dehumidifier working around the clock, keep an eye on how the desired humidity levels are affecting your worm bin.

4.  Harvest Castings and Add Bedding

By now you’re aware of the value of vermicast or worm castings.  The nutrient level and availability of those nutrients far surpasses that of conventional compost.  A lesser known characteristic, however, is how well worm poop retains water, able to hold 2 to 3 times it’s own weight in moisture.  This is wonderful in your garden or flower pots, nbut maybe not quite as helpful in a worm bin.  It is very easy in a plastic bin to find moisture levels that can turn your bin from a healthy, pleasant smelling aerobic environment into a malodorous nightmare for your house and your worms.

You may also choose to add more bedding (peat moss, shredded paper, coco coir) instead of – or in addition to – your worm castings harvest.

5.  Use Dry Cardboard or Newsprint to Regulate Moisture

If you open the top of your worm bin and find condensation on the bottom side of the lid, you may be at or approaching the top end of your humidity level.  Since I don’t care to leave the bin uncovered, I will often layer newsprint or some dry cardboard on top of the bedding, which wicks some of the moisture out of my bedding.  It’s an inexact technique, but it may help buffer your moisture levels.

Maintaining appropriate moisture is not that difficult.  But letting it get out of control can spell doom for your worms.  A little vigilance alongside following these guidelines should steer you clear of calamity.  If you have anything to add, let me know in the comments!

17 thoughts on “5 Tips To Keep Correct Moisture In Your Worm Bin

  1. I have just harvested the contents of 6 rubbermaid totes, the only alteration was to install four 3 inch vents in each tote, the moisture in the compost varied widely from semi mud to semi dry. Hoping to correct the situation I will try to formalize my feed and also line the totes newspaper. Any suggestions would be greatly appreciated. Also what would you recommend for storage I’ll have about 10 gallons

    1. Hey man,thanks for the comment! Rubbermaid totes are tough for that very reason. I think simply mixing the vermicompost will help even out the moisture levels in your case. As for storage, somewhere near a normal 72-degree room temperature in a breathable bag like a sand bag would suffice. You might consider laying a damp towel over it to help transfer some moisture without completely saturating it. You simply want it to breathe without evaporating away all of the moisture.

  2. i purchased a 20lb plastic bag og castings 3mo. ago was told do not let them dry out i thought that ment to keep plastic bag closed tight. however when i open bag there is lots of large balls an most have white stuff on them. i was told they are drying out to moisten them but to much will make mud.how do you know when is enough? LOST

    1. Hi Kenneth,
      It sounds like you may have mold growing on your castings, but I’m not sure.
      While you don’t want to let them completely dry out, keeping them sealed in a plastic bag isn’t advised either.
      When I am not using mine, I keep them in a bucket inside or in the shade and I will cover them with a wet towel that allows them to breathe without drying out too much!

  3. Hi Steve, I’m wondering how to balance the need to add bedding along with feedings, and trying to end up with a consistent compost to harvest. If I have to keep adding bedding, how do I end up with compost that has no bedding in it? Thanks.

  4. I keep my worms in a disused bath tube. I have used aging horse manure together with some semi-composted dry leaves. I also feed my worms with melons, bannanas, and cantilopes, paw,paw (which they love). I admit to overfeeding!

    Its summer here and I have noticed some creepy crawlers, mites?, bugs?, tucked under the cantiloppes, and honeydews -which I normally break in two halves with the exposed juicy bit tucked into the worm’s bedding and the hard surface showing but covered with card board.

    I am not sure these scary looking mites? buds etc are not also feeding on the worms themselves?

    How to get rid of them or at least control their numbers?

    I criten grubs, and other

    1. Hi Al,
      Yes, those mites are from the overfeeding and the excess moisture from the halves of the melons. The mites aren’t a problem by themselves but they do indicate that things are too wet in the bins. They will not attack your worms unless the worms are in distress. If this is happening, you would see evidence of it in the bin.

      1. I also have lots of reddish brown mites, which I believe are earthworm mites. What do you suggest to get rid of them?

  5. Steve, I just started my worm composting bins about a week ago. I have two twenty gallon rubbermaid totes that I drilled lots of small holes in the bottom, sides, and top then added peat moss , damp cardboard, and worms. One bin has one pound of red wigglers and the other has two pounds of African nightcrawlers. I am feeding them about half of their weight each day with kitchen scraps. This seems to be working but I wanted to know if I should keep adding peat moss on top of the kitchen scraps? When should I expect the worms to lay eggs? Thanks

    1. Hi Edward,
      It can take a few weeks before the worms acclimate enough to begin producing cocoons, but if the conditions are right, it will happen. And adding dry bedding (whether paper, peat moss, or coco coir) is always a good idea.

  6. I’m a beginner and I notice a lot of little white mites, 2 different looking ones and I have a high powered microscope and took a look! YIKES!! Some white see thru with ant looking like shape but a longer slender back end, and then another type kinda orb shaped. Do you have an idea of what they are specifically.

  7. Pingback: Why Are My Worms Going To The Bottom? – Bescord
  8. How do you best water your worm bin? Mine is inside right now and new to me. We have forced air heat which dries everything out. I have damp newspaper over all and everyday I lift it and mist the soil. It seems like a lot of work and a delicate balance. I want to succeed and keep it properly moistened.

    Secondly, do you add food even when there is plenty of food? If so do I take any out so there is not too much?

    1. Hey Sherry- Using a mister daily works great. Many people who live in drier climates or who have dehumidifiers in their homes deal with this. You can try to trap more moisture in by putting a piece of bubble wrap, cardboard, or a jute cover that we offer on our website on top of the material.

      It will be best to always wait until food scraps are mostly broken down before adding more food. Keep it to a layer about a quarter to half an inch thick. We have a Wiggle Wednesday video on YouTube that discusses this topic. I’m including the link below.


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