The Truth About Salt in Worm Compost

The Truth About Salt in Worm Compost

Has it actually ever occurred to you that worm compost could even have salt issues? It came as a surprise to me! Somehow I didn’t equate my food scraps with toxic salt levels.

But that’s me. I’m not much of a worrier. I sometimes kinda jump in and figure things out as I go along.

Luckily, worm composting is a perfect platform for just that kind of free-spirited recklessness! But could that be dangerous? Might a happy worm farmer like me (or you?) be caught unaware… of too much salt in their worm bin?

Not today, cowboy. 

How does salt in worm compost affect worms?

First of all, let’s learn about salt.

According to, “Salt is a crystalline compound, sodium chloride, NaCl, occurring as a mineral, a constituent of seawater, etc.” Sure, that’s interesting, but there is one very important thing that it doesn’t mention.

Salt is hygroscopic, which means it absorbs or attracts moisture from the air… or anything else it touches.

Salt in the worm bin draws moisture out the air, bedding, and skin the worms live within. At nearly 90% water themselves, a worm requires very humid living quarters to stay well-hydrated.

And what’s so important about being well-hydrated?

It’s a matter of life and death. A red wiggler breathes through a slippery mucous membrane instead of the lungs. Drying out means they suffocate and you lose your worm work-force.

Does salt affect the quality of my worm compost?

Worm compost is a highly valued resource in the gardening world. It’s shown to heal soils, bring about lush verdant growth, and restore balance to barren areas. It bumps up the productivity of fruiting and flowering plants and is even called Black Gold!

However, when salinity offsets the critical balance- worm compost is no longer as effective or valuable. University of California Agricultural and Natural Resources poses that high salinity both prevents plants from getting the water and nutrients they need, while also toxifying them.

Effect of Salt Toxicity in Plants

Over time, the soil of many potted, garden, and landscape plants can become over-salinated. Interestingly, the addition of BALANCED worm compost and worms to salty soils has been shown to help reduce and reverse salinity in some areas.

Are your plants telling you their soil is too salty? This is how you might know:

  • Wilting during hot, dry conditions
  • Reduced plant vigor
  • Flower and fruit development delayed and/or smaller than normal
  • Fewer and/or smaller leaves than normal
  • Discolored foliage
  • Nutrient deficiencies

Despite the potential effects, the University of Massachusetts Amherst Center for Agriculture, Food, and the Environment shares some hope, “The extent of damage can vary with plant type, type of salt, freshwater availability and volume, movement of runoff, and when salts are applied.” Which leads us right into our next point.

How does salt in worm compost rise to dangerous levels?

Believe it or not, this could happen to anyone. It’s happening in all of our bins, all the time. Really. The buildup of salt is unavoidable- to an extent.

Salt shows up in the sneakiest places. No wonder it so easily ends up in the worm bin. Here are the most common sources to be aware of:


Coconut coir is one of the most common bedding starter materials. It’s great because it has super absorption, and allows for drainage as well as superior airflow. Unfortunately, coconut coir also retains a great deal of salt absorbed from the air and seawater where it is grown.

Food Scraps

Most natural food has at least a trace amount of sodium. Additions like those hardly make a difference. But just as often it’s our leftovers, our prepared foods, that end up in the worm bin. Were those foods cooked with seasonings? Add to that anything processed and already, the salt levels are soaring.


According to the Soil Guy, “Actively growing vegetable crops requires a continuous supply of balanced nutrients in the soil. Unfortunately, these are usually provided by the application of synthetic fertilizers which include soluble salts .”

As these accumulate, roots are damaged and eventually the tops as well. These commercial crops are the same ones that become our food scraps and thus, worm food in the worm bin.

Rock Salt

Plentiful, effective, and relatively cheap, de-icing salt is a winter lifesaver. But 22 million tons a year make their way into our soils and waterways.

Many of us use grass clippings, yard waste, and soil to feed our worm bins. How much of that comes from along walkways or roads that were covered in salt just months ago? Where is that salt now?


Another significant source of salts is in our irrigation water. Yes, the same water we drink from the tap and use to irrigate our plants has measurable amounts of salt in it.

As the water in the worm bin evaporates, it leaves behind the heavier elements that make up salt, sodium (Na), and chlorine (Cl). Over time, these accumulate, raising the overall salt content of your worm bin.

Is it too late?
How to Prevent or Reverse Toxic Levels of Salt in Worm Compost

It’s never too late. To find some solutions we need only look at the sources of all that salt.


If opting for coconut coir, just rinse and repeat! That’s not so hard. But other bedding choices work just as well without the need to rinse and repeat. Dry leaves, shredded cardboard, partially complete compost; a combination of things is best.


Only add what red wigglers can eat to the bin. Be sure to rinse all food cooked with salt before feeding it to your worms. Avoid adding foods that are processed or packaged as they are likely to be higher in sodium.


Avoid commercially produced foods as much as possible. Avoid using fertilizer on gardens and lawns that will be used as worm food.

Rock salt:

Be aware of what has been used on your property. Try to steer clear of using materials off the edges of sidewalks, driveways, and roads.


This one is key but in a different way. Proper drainage out of your worm bin is the best way to desalinate your worm compost.

A nice worm compost pour-over will rinse away much of the salt that has gathered over time. This can be tricky if you’re using a storage tote.

If that is what you have, drilled holes along the bottom and sides will provide a way out for that excess water. Lift your bin onto bricks to let the water flow freely from the bottom.

If however, you are composting with a Worm Factory 360 or other tray-style composters, a clean water flush will be much easier. Simply lift the top lid and use a watering can or pitcher to direct the flow of clean water over every bit of the top level.

How much you use depends on how full of worm compost your tower is. You want to use enough so that what goes in will be able to filter all the way down and out. Be prepared; the catch basin at the bottom will fill up with leachate!

Here’s an opportunity you don’t want to miss.
Collect that leachate to make a fresh batch of worm compost tea.


Now this one is my favorite because it’s a sure way to actually rid the bin of any material that may harm the worms. Every few months you should be able to harvest a load of finished compost. Whatever you remove can go right out into the garden or grass, along with the salts that will soon be washed away by the rain.


Worms who rely on a moist environment have a low tolerance for super-salty conditions. Keep your workforce happy with a low-sodium diet and proper worm bin maintenance. A regular schedule of harvesting will ensure the buildup stays to a minimum.

If any of this sounds like a lot, don’t worry, The Squirm Firm is here to help. Let’s worm together! Sign up here and once a month we’ll send you a free newsletter filled with tips, tricks, and expert advice to keep your worm composting fresh!

Thanks for doing your part to reduce waste and heal our soil! We appreciate you.

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Happy worm composting,


Readers Comments (9)

  1. Francesca, Thank you for this very thorough description of salt and its’ effects on our little buddies (worms). If I understand your information correctly, can one determine the salinity of the compost being generated in the Worm Farm 360 and correct this before the compost is harvested for worm tea or compost?
    I’m so grateful for your wealth of knowledge and the clear and concise way you present this information.
    Respectfully, Bruce

  2. Ty,
    I learnt something new.
    I compost and do have two worm beds.

  3. Thank you for the warning about being sure to rinse coconut coir, Francesca! I wondered why so many of my worms seemed to disappear when I rehydrated a brick of coir, mixed it with newspaper & cardboard, and tucked the worms in. Eeeeeee, poor things. They probably got dehydrated. 🙁

  4. Hello, my name isNate and you mentioned using the leachate from the worm bin…that is something nobody should use it is filled with sodium and is bad for plants, you should really discard of all leachate and stick to making or purchasing worm tea made with castings, it is safer and wonderful results all year round. I make worm tea constantly and pour over all my plants and the yeild and growth is through the roof, im not trying to start any problems im all about the facts and truth in everything just try to help, God Bless all.

    • Thanks for your input, Nate. You are right on target with much of what you’ve shared. Leachate will never be a consistent product. You can never assume exactly what is leaching out of your worm bin. In fact, there will be times that your leachate is higher in sodium than ideal for some plants. It can be full of stinky bacteria, and a low pH too- that’s why we’d always, always dilute it and aerate it if possible before using on safe areas of the landscape. Never directly onto plants that are edible. But for sure, worm compost tea is the way to go if you really want a high quality liquid fertilizer. I consider leachate bonus material that’s good for adding back into the hot compost too.

  5. Just harvested my first batch of castings! I was given a free slightly used worm composting system similar to a 360. Came with kelp? Rock dust. Bought some worms locally from a friend ( mostly juveniles and cocoons, maybe 3/4 of a pound) . 13 weeks later I harvested the 1st tray, with a second tray completely full and well established. I started a 3rd tray using everything I sifted from the castings in tray#1 plus rinsed coco coir and torn up egg cartons.

    I decided I just had had to save the cocoons! Spent 2 full days picking out cocoons before sifting the big bits of paper out and pieces of corn (I won’t put corn in there again) . I found nothing else but the uneaten paper and corn shells and a few longer fibers from the coco coir. I saved at least 300 cocoons. Getting the worms to migrate down was easy. Only found a few worms. The worm population has doubled if not tripled, lots are adults. I feel I need to keep 2 full trays going so they have enough room.

    The castings look, feel and smell amazing! After 2 applications a week apart in our vegetable garden. The plants look much greener and have grown tremendously!

    Things I do with food:
    After the first feeding I got a face full of fruit flies. Food was buried and covered with newspaper. So now I spend a few minutes once a week and run my scraps through the blender adding egg shells ground in a coffee grinder to a fine powder a little used coffee grounds, tiny pieces of egg carton or brown paper and a little mineral powder and freeze in portioned containers. Not 1 fruit fly since. I found they plow through the food faster and it doesn’t sit long before they are all over it.

    My bin is in the laundry room in air conditioning since I live in Florida. There’s no smell. The temperature is 73-77 humidity inside the bin is 80-82% consistently. It’s completely dark with the light off and door closed. No worm has tried to escape! The washer, dryer and air handler noise doesn’t seem to bother them.

    Bedding: 1st tray: organic coco coir , cardboard run through a micro shredder.( I sifted a lot out of the castings) A little torn up newspaper -it disappeared . Egg shells ground by hand. I can see this in my castings. I bought a coffee grinder for my eggshells now I’m only going to add to the food. Is this okay or not? Does it need to be distributed to th I was hoping I couldn’t see them in the castings this way….2nd tray has coir, leftover bits of cardboard from tray 1 and egg cartons torn up .Tray 3 has coir and egg cartons only. I use some strips of brown paper to line the spot where I Dig a hole and feed to sop up some of the moisture. That paper disappears too. I feed 3 times a week usually. I’ve tripled the amount at each feeding since I started. I check to make sure food is almost gone before adding more. I fluff all the bedding once a week, avoiding the place I last fed , to distribute the moisture. It gets dryer on top and kind of wet towards the bottom and this helps and I enjoy digging around in there!

    Anyone thinking they might want to try composting with worms I say go for it! It’s really simple once you learn the basics. You can be put minimal effort with huge rewards.

    • Thanks for your detailed breakdown of how you’re finding success with worm composting. It sounds like your well-oiled machine is paying off in huge ways! Awesome, keep it up!


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