Outdoor worm bin, subpod, composting with worms outside

Outdoor Worm Composting: The Complete Guide with Outdoor Worm Bin Options, Tips, & What to Avoid (2022)

A common question we receive from customers in early summer and late fall is “can you compost with worms outside” in the winter or summer? Many people rightfully worry that harsh temperatures can harm or kill their worm population. Although there are a few risks, you can absolutely be successful worm composting outdoors - as long as you follow a few basic rules that will your compost worms the best chance at survival as temps rise and fall.

Why Outdoor Worm Composting Works

Composting with worms outside is done by individuals and professional worm farms for a variety of reasons, including:

  • Worms simply compost and breed better outside in a natural setting - everything from natural soil and microbes to air flow create conditions favorable for a thriving worm population.
  • Outdoor worm composting opens up a larger space so more of your food, yard, and organic waste can be vermicomposted (allowing you to divert more waste from landfills and generate more black gold - aka worm castings - for your garden, lawn, and house plants).
  • You will get outside more caring for and working along side your wiggly friends!

Outdoor Worm Composting: The #1 Critical Success Factor

The most important factor in outdoor worm composting is creating conditions that mimic those that worms use to survive in nature - namely an outdoor worm bin with enough surface area and vertical depth for the worms to find safe temperatures if surface conditions get too hot or cold. The more extreme the weather in your area, the more your outdoor worm composting needs to mimic natural conditions worms are accustomed to.  

In terms of options for outdoor vermicomposting, the most common are in-ground planters, compost piles, windrows, or outdoor worm bin structures 3x3x3 feet or greater in size.

Outdoor Worm Bin Options

If you’ve read this far you’re probably interested in the different types of outdoor worm bins. The great news here is that you can get very creative in the type of outdoor worm bin you use. Have an old bathtub, trough, or a bunch of 5 gallon buckets lying around? They can all be repurposed as outdoor worm bins. 

In addition, there are outdoor worm bins manufactured specifically for worm composting and many other structures you can buy and easily convert to an outdoor vermicompost bin. Not interested in building or buying a worm bin? That’s not a problem either as compost piles and windrows work very well for outdoor worm composting.

Here's a summary of the options to consider for your outdoor worm composting set-up:

Structure

Type

Summary

Plastic 5 Gallon Buckets

In-ground

This is an easy and very affordable option - simply drill 5 ¼ in holes in the bottom of the bucket and 10-12 ¼ in holes on the side of the bucket’s lower half. 

Next, find a shady spot in your yard or garden, dig a hole, and plant the bucket in the ground (the top of the bucket should be at ground level). 

Place topsoil or other bedding (coco coir, peat moss, or shredded cardboard) in the bucket to a depth of 6-8 inches (the bedding should be above the hotels you drilled on the side of the bucket).

Then place ½ to 1 lb of worms in the bucket and place food on the surface of the bedding. The worms will eat the food and bedding and also crawl out through the holes into the surrounding areas of your yard or garden.

Compost Pile

Above ground pile of organic matter

For outdoor worm composting, we recommend only using compost piles with organic yard waste (e.g., leaves, grass, branches) and/or vegetable and fruit food waste (no dairy, meat, etc).

Simply moisten an area of your compost pile and add worms. One important factor to keep in mind - the heat in hot compost piles can harm worms or cause them to leave the pile. It is a good idea to add your worms to a cooler or fully composted section of your pile. 

Windrow

Above ground pile of organic matter

Windrows are often used by commercial worm farms for growing and breeding worms. 

Windrows are very similar to compost piles. They can be an active compost pile or already composted material and waste that won’t heat up and harm the worms. 

In outdoor worm composting, windrows usually consist of bedding (composted material, composted manure, spent brewery grains, peat moss, top soil, etc) and feedstock for the worms is placed on top of the windrow. As worms process the feedstock and produce castings, more feedstock is added and the windrow grows in size over time. 

Eventually the windrow will be “harvested” using a tractor and sifter or trommel, which separates the worms from the castings. Then the process starts all over again with a new windrow.

Subpod

Manufactured Worm Bin (above or in-ground)

Subpod can be purchased online and then used as an outdoor, above ground or in-ground worm composting bin. We sell the Subpod in our store at Brothers Worm Farm and it is a well-reviewed product by customers.

Structures at least 3x3x3’

In-ground or above-ground and include:

  • Wooden Boxes
  • Plastic Storage Bins
  • Garden Beds
  • In-ground Planters
  • Steel Raised Planters or Stock tanks

Outdoor worm composting structures can be set-up similarly to windrows -  bedding (composted green or brown waste, composted manure, spent brewery grains, peat moss, top soil, etc) is placed in the structure to a depth of 6-8 inches. 

Worms are placed in the structure and feedstock for the worms is placed on top of the bedding. As worms process the feedstock and produce castings, more feedstock is added until the structure is full and the bedding and feed are fully processed into castings. 

 

Tips for Keeping a Worm Bin Outside in Winter or Summer

Keeping a Worm Bin Outside in the Winter

If you live in a colder climate and have an above ground outdoor worm bin, cover it with a tarp (or hay bales, really any material that can withstand winter ice/snow/cold). If your bin is in-ground or in a windrow, there isn’t much to do when winter comes except to wait for spring time when the worms become active again and start breeding again. Just remember that the more extreme the temperatures are in your area (e.g., sustained temps below 20 degrees F), the more important it is to have an in-ground worm bin or compost pile/windrow where the worms have access to the ground where they can find more moderate temperatures.

Keeping a Worm Bin Outside in the Summer

If you live in a warm or hot climate and you decide to have an above ground worm composter (e.g., raised garden bed), it’s also important to provide the worm bin with shade. This can be either trees or a shade cloth - the key is to ensure the outdoor worm bin isn’t getting full/direct sunlight for most of the day. Note that this applies to above ground worm bin structures and isn’t as important if your outdoor worm composting is done in the ground or with a windrow or compost pile.

Bedding & Feedstocks for Outdoor Worm Bins

When considering your set-up for an outdoor worm bin, it’s good to think through what you will use for bedding and feedstock. Usually it’s best to use those materials you have access to - this can be either kitchen waste, compost, composted manure, topsoil from your yard, or other decayed organic matter. 

Following are recommendations for bedding and feedstock for compost piles, windrows, and other outdoor worm bins.

Outdoor Worm Bin Type

Bedding & Feedstock

Compost Pile

This one is easy - worms love compost and usually thrive in a compost pile. As mentioned above though, it’s important to have areas of the pile that aren’t too hot so before introducing worms make sure a part of the pile has been through several heat cycles and is no longer active.

Windrow

Common bedding and feedstock for windrows are composted manure, compost, composted spent/brewery grain, and yard waste (e.g., e.g. grass, leaves, branches). Topsoil, cardboard, and peat moss are sometimes used as well. Note that leaves heat up when breaking down so we recommend composting them first or mixing them in with other material that won’t heat up.

In-ground or Above-ground Structure

For smaller structures (less than 3x3x3 feet), topsoil, shredded cardboard, peat moss coconut coir, or composted organic matter all work well. For larger structures, compost, manure, and the other items noted above for windrows are great options!

 

Outdoor Worm Composting: FAQs & Things to Avoid

When planning your outdoor worm composting approach, there are a few things to avoid. We’ll answer these through common FAQs we receive on outdoor worm composting:

1) How many worms should I add to my outdoor worm compost bin?

If you are new to worm composting we recommend starting small with ½ to 1 lb of worms. Once you have the hang of things you can add more worms or just wait for the worms to breed and populate the structure.

If you are more experienced with worm composting and want to process as much waste as possible, we recommend 1-2 lbs per square foot of bin space. This is the density that most professional worm farms target for vermicomposting.

2) Can I use my compost tumbler as an outdoor worm bin? 

We don’t recommend using compost tumblers for a couple of reasons:

  1. Compost tumblers will heat up too much, causing the worms to leave (or perish).
  2. Compost tumblers usually aren’t large enough to protect worms when conditions get too hot or too cold in the summer and winter.

Compost tumblers are great for creating compost for your worms, but put the worms somewhere else where they can thrive.

3) Can I use my indoor worm bin outside?

Indoor worms bins (e.g., Maze Farm, Urban Worm Bag, etc) aren’t great options outside for the following reasons:

  1. Most indoor bins aren’t built to withstand the elements and they are too small to offer worms protection during summer and winter temperature changes .
  2. Most indoor worm bins are not water tight, so rains will infiltrate the bins and can drown the worms (worms love water, just not too much of it!).

Indoor bins “can” work in carports, garages, and other areas that offer some protection from the elements, but if you live in areas with extreme temperatures (e.g., Texas in the summer or Wisconsin in the winter), these bins will likely not protect the worms from the weather.

4) Can I just use my garden for outdoor worm composting?

Yes - sort of, it really depends on your goals. Worms only eat decaying organic matter (they won’t touch living matter like roots or leaves), so they usually do well in a garden. 

However, having worms in your garden can make it difficult to vermicompost your excess organic waste as this set-up requires that you place the organic matter in your garden rows for the worms to process. And if your goal is to produce worm castings, harvesting the castings from a garden can be very difficult. 

If your goal is process waste and create castings, we recommend doing it in a different set-up or structure than your garden (having a small area near or part of your garden just for vermicomposting can work well!).

Harvesting Castings from an Outdoor Bin

We’ll close this post with a few thoughts on the last item folks usually think of when starting a vermicompost practice - harvesting castings. It’s good to start with the end in mind as castings need to be harvested periodically so that:

  • They can be used in your garden, lawn, or with houseplants
  • Worms aren’t living in them indefinitely (castings are toxic to the worms over time)

For compost piles and windrows, we recommend leaving space at the end of the pile or row for adding fresh bedding or compost. As the pile or row begins to get fully processed by the worms, set up the space you have set aside with compost (for the compost pile) or fresh bedding (for the windrow). The worms should migrate to that area as they run out of a food supply in the already processed areas.

For outdoor structures, similar to handling compost piles you can leave space in the structure to place new bedding and food so that worms can migrate there when the main area is fully processed. Or, allow worms to process the bedding and feed in the entire structure and then separate the worms from the processed castings as follows (this also works for windrows and compost piles):

1) Worms don’t like light so the idea here is to subject them to some light and encourage them to congregate in an area where you can easily separate the worms from the castings.

2) Form a pile by dumping or shoveling the contents of the outdoor worm bin on a tarp. If you have a larger structure you will need to make multiple piles (if the pile is too big the worms may not migrate to the bottom).

3) Wait an hour or 2 hour and most of the worms will migrate to the bottom of the pile.

Note - we recommend doing this in a shady spot so the worms aren’t subjected to too much direct sunlight or heat. If shade isn’t an option, cover the pile with a shade cloth.

4) Scrape off the top of the pile until you start to see worms in the lower areas of the pile.

5) Wait another 20-30 minutes until the worms move lower in the pile. Scrape as much of the pile as you can until you start seeing worms. Repeat steps 4-5 util you have a thin (1-2 inches) top layer of castings with the worms congregated underneath.

6) Once you reach this point it is ok to take the worms and the thin layer of castings and place them back in your structure (which hopefully has been set-up with fresh bedding for the worms!).

Thanks for reading and good luck with your vermicomposting! If you have questions please reach out to us at highfive@brotherswormfarm.com or through our contact us page.

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