Hot Weather Vermicomposting: 7 Tips to Beat 100°F Temps

Worms may be simpler creatures than humans, but they need what we need: food, water, and protection from predators and the elements.

One of these elements – heat – is cause for concern. And it’s far worse than cold for the health of your worms.

Even for indoor worm bin owners, the summer heat can cause problems.

This article will touch on why excess heat is far worse than excess cold and what you can do to keep your worm bin cool in the hot summer months.

Hot Vs Cold in the Worm Bin: They’re Not the Same

Most composting worms are best kept in the 72°-80°F range. And the accepted conventional wisdom is that worms will be fine between 55°F and 90°F.

You may envision a bell curve where the peak performance of the worms is at 72°F. You might expect a slow and symmetrical decline in performance in either direction like the image below.

This is NOT representative of how temperatures will affect your worms.

If you go below 55°F, what you’re likely to find is that worm reproduction and waste consumption declines slowly, eventually grinding to a halt. At temperatures near freezing, a full 20+ degrees colder than 55°F, the worms might survive.

Interestingly, the cocoons will almost surely survive as cocoons stay in viable in frozen material, ala Hans Solo from Return of the Jedi.

So in cold temperatures, things go south sloooooowwwwllly.

But if your vermicompost gets more than 10 degrees warmer than the 90°F limit, things go south in a hurry.

Unless your worms have somewhere to retreat to, you can expect all of them to die very quickly.

So here’s what you can do to manage high temperatures in your worm compost bin.

How To Keep Your Worm Bin Cool in Summer

#1: Do Nothing

You read that correctly.

If you’re on my e-mail list, you may remember an e-mail I did about keeping a worm bin warm in winter. Part of this post dealt with the concept of the natural insulating properties of a large worm bin.

While the outside temperatures are a big deal, what really matters is the temperature inside your vermicompost.

A nice, large full worm bin will provide a damping effect against temperature extremes due to thermal mass, ie, the ability of the material to absorb and store heat. Obviously, larger worm bins like the Urban Worm Bag can help provide more of this damping effect due to the higher volume.

The larger your worm bin is, the longer it will take to heat up. This means your vermicompost should be cooler than ambient temps during the day but possibly warmer than ambient temps during the evening.

The graphic below shows how thermal mass works to buffer against temperature extremes. The blue line represents the temperature inside your vermicompost.

So you might – and I stress might – be OK without doing anything.

#2 Keep Your Worm Bin In a Shady, Ventilated Area

This is kind of a no-brainer, but if your bin is subject to direct sunlight, you’re going to have a much tougher time keeping it cool enough. Get it into an area where it won’t experience direct sunlight, especially in the middle of the day.

Also, try to place it in an area with plenty of ventilation to draw excess heat away from the bin.

Believe me, I have many Urban Worm Bag customers who experience great results on shaded porches in Texas.

#3 Reduce the Feeding

The introduction of nitrogen-rich food waste into your worm bin can stimulate microbial activity which can raise temperatures in your bin.

I’m not talking about preventing full-on thermophilic hot composting. I’m talking about the mild increase in temperature that occurs after a rich feeding.

To reduce the risk of sending temps into the high-90s in hot weather, consider dialing back your feeding which will dial back the microbial activity.

And no….you will not starve your worms. You could stop feeding them today, forget about them for weeks on end and they’ll survive.

#4 Add Bottles of Ice

Lots of folks use this handy little trick which is to place frozen water bottles on (or in) their vermicompost.

The effect is temporary and you’ve got to stay on top of it, but this seems to work for lots of vermicomposters.

If you go this route with a storebought water bottle, drink a few sips out of it before freezing or the expanding ice may rupture your bottle.

Note: Do not add actual ice to your vermicompost as that would get your bin way too wet…and likely too hot as well!

Hint: Cooler packs are a great idea too!

#5 Try Evaporative Cooling

This one is a wee bit more involved but you could take the top off of your worm bin (or unzip the top of your Urban Worm Bag), drape a wet towel over the top of your open worm bin and run a fan over the towel.

This will work better in a more arid climate like Colorado or Arizona. Evaporative coolers work better when there is a significant difference in humidity between the drier outside air and the more humid, cooler air you’ll be trying to push into your bin.

I have not yet tried this technique, but I have some readers in the Southern and Southwest US who swear by it!

This handy YouTube video details some interesting DIY techniques for creating evaporative or “swamp” coolers.

#6 Use Reflective Solar Material

Many thanks to longtime reader Shaul for this handy bit of advice.

If you can’t shield your worm bin from direct sunlight, then deflect it with a solar reflective cover.

While there are no off-the-shelf solutions for bins like the Urban Worm Bag (yet), you can buy an inexpensive roll of reflective material and drape it or cut it to fit over your bin.

#7 Move the Bin Indoors

We’ll put this one in the “No Sh&t, Sherlock” advice category, but if your housemates can tolerate having your buddies indoors at least for the summer, then this is your best option.

To keep the peace with your worm-skeptical co-habitants, it may be best to scale the feeding way back to reduce the risk of fruit flies and other critters.

If you want your worm bin out of sight, then basements and utility rooms are great places for them!

Summary: If You’re Not Cheating, You’re Not Trying

“Work with nature” is a common mantra in composting circles and in most cases, that mindset can lead you to success with vermicomposting.

But if you’re working with a manmade worm bin, then sometimes you need manmade help to harness the natural wonders of worms.

So there’s no shame in using air conditioning, fans, solar reflectors, frozen ice bottles, and shade from porches to keep your vermicomposting journey alive.

How are you guys keeping your worm bins cool? Let me know in the comments below!

Want to Learn More?

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14 thoughts on “Hot Weather Vermicomposting: 7 Tips to Beat 100°F Temps

  1. A note for evaporative cooling. You’re right about arid climates. Here in Kansas with our high humidity, swamp coolers aren’t much good. Past about 75-80 degrees F. they just make the air heavier.
    Evaporative cooling may work outside, but inside an insulated structure it’s pretty much a lost cause.
    Keep up the good work & God Bless. <

    1. I always appreciate your insight, Wayne! Makes you wonder why they call them swamp coolers when they don’t work in the swamp! 🙂

    2. What’s worked best for me. Is to create a connector between earth and your bin. So the worms can go in and out of the bin and into the soil beneath it where it will be much cooler. They won’t all run away, because they’ll stay where the foods at! That and shade is all you need.

      (SOUTH GEORGIA weather, 100 degrees is the norm for many months of the year with hunidity almost always 80% and up.)

      1. A”Subpod” that can be buried in a garden does just that, have had one for several years now works well. Just don’t put to much green waste or you will cook your worms. Speaking from experience.

  2. We have had Temps. Here up to 110 outside. In the room where I have the UWB,Temps. Reach over 100 degs.
    I use 2 .5 gal ice bottles morning and nite change when ice melts and re freeze.bbag is .75 full and Temps. Range from high 70s to mid 80s. Works good for me. Happy Worms. So far.

  3. I use Reflectix form Lowes for my 4×12 flow thru beds. It keeps the moisture in, blocks light and the worms love the bottom side. Not exactly cheap but it works very well.

  4. We had some “extreme” Temps for Oregon, reaching 117 degrees F a couple days, my worms survived outside simply by keeping in shade. I am going to try the frozen water bottles as we have another extreme heat warning ⚠️.

  5. Hey Steve;

    I’ve got several 2×4 homemade flow thru bins which I keep in a shed. To keep bins cool in high temps I just add a “little!” more moisture to keep them from drying out. I’ve found that even though the temps in the shed can reach over 100+ degrees the evaporative cooling keeps bin temps at about 78 to 82 degrees. The trick is to add enough moisture to keep the bins from drying out.

  6. My Rubbermaid bin is in my unfinished basement, but I did notice the bin temp reaching for 85 one day. Now when it reaches 77 or so, I add frozen food. I put bedding below and above so it doesn’t touch the worms. I figure it takes a day or 2 to defrost and the bin gets back down below 75.

  7. Good Idea with the plastic water bottle, I was considering adding Ice but was worried about excess water, my first vermi summer is around the corner, and the Cairo sun can get up to 38-44C.
    I’m getting a kitchen thermometer to keep track as well, might use insulation if necessary but let’s see how things go first.
    Thanks for the info!

  8. I live in New Orleans, hot and humid. I use freezer bags from a weekly meal service. At about 80 degrees I plop one on the top of the inner cardboard cover (I think it gives some insulation to the worms and bedding material) The worms still work in the upper part of the bin and the condensation has been enough to cheap the bedding damp. Don’t let the bag leak it contains some sort of chemical that probably would not be good for the worms.

    WARNING don’t believe everything you read on the internet, I am no expert nor do I have any scientific proof. But seems to work for me so far.

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