Outdoor Worm Composting in Winter – To Do or Not To Do?

Most people start their worm farm in spring, get it up to full worm castings production mode in summer, a little less in autumn and then start worrying about outdoor worm composting in winter.

In this article you will find everything you need to know to protect your worm population against freezing temperature and help them survive cold harsh conditions. So come next spring they are ready to get back to do what they do best: turning plant based food scraps into natural, organic fertiliser and soil conditioner.

How Cold is Too Cold for Red Wigglers?

There are several temperature ranges to look at. One is the range of temperature where worms are most active and the second is at what temperatures do red wigglers stop eating and reproducing and when does it get dangerous for them.

IDEAL temperatures for red wigglers: 18-25°C (64-77°F)

This is the range where they will eat and have the highest reproduction rate (more info on ideal temperatures for red wigglers here)

TOLERABLE (Survival) mode temperatures for red wigglers:
0-16°C
(32 – 60°F)

These colder temperatures can be endured by red wigglers. However, they will eat much less and stop mating and laying cocoons. They are likely to move to more comfortable areas if they have a chance to do so. 

TOO COLD for Red Wigglers: Less Than 0°C (32°F)

Below freezing point, red wigglers are in danger to literally freeze to death. They have a high percentage of water in their bodies and frost will damage their cells.

Note: I have seen several worms still alive after they were emerged in water, under ice, inside a lump of spent mushroom compost. The tub had frozen overnight and there was a quarter of an inch of ice on top. I was pleasantly surprised to find the worms (which I didn’t know were in there) the next day when I retrieved that bit of compost. 

Red wiggler cocoons can survive freezing temperatures unlike their parents. So don’t worry, if you missed saving your worms from the cold, at least you should have cocoons ready for next spring. They will hatch when the weather warms up.

6 Ways to Prepare Your Worm Farm For Winter

1. Feed Less

For stackable, smaller worm bins: Fresh vegetable scraps will need much longer to decay. Coupled with less activity from worms at lower temperatures this can quickly lead to a rotting, smelly mess. Therefore, for temperatures between 10-15°C (50-°F) feed very little and monitor carefully how much the worms consume.

Below 10°C (50°F) you will need to add very, very little if any food. 

Larger worm farm designs can still take in vegetable scraps over winter. Even if they are not consumed by worms right away, larger amounts of fresh nitrogen rich food like most kitchen scraps can heat up easily and in fact can be a source of heat even in winter. That way the composting keeps going.

2. Do Nothing

This isn’t as stupid as it sounds. It’s always worth considering the option that requires the least input in work and energy.
As explained above, red wigglers lay cocoons before it gets too cold for them. Those cocoons will survive even frost and hatchlings will appear in spring providing you with new worms for the next season.

If you live in an area with mild winters where temperatures rarely go below freezing and even then not for long chances are that your worms survive as well.

3. Move a mobile worm farm to a warmer, sheltered place

Do you have space in the garage, cellar, pantry, greenhouse, conservatory, a hallway or kitchen? Finding a spot where the surrounding temperature is safely above freezing is the best way to keep composting during the colder season. I would highly recommend indoor worm composting if you want worm castings ready in spring when sowing and planting begins.

If you keep your worm farm in the house don’t be surprised if you find yourself keeping a closer eye on it than usual. Just make sure your pets can’t get at it.

4. Insulate

This is a compromise between ‘Do nothing’ and ‘Building a winterproof worm farm’. Adding even a lose insulating cover like a carpet, bubble wrap or moving blankets can make a difference for the odd spell of frost. 

5. Provide a heat source

You can always rig up a source of heating inside a worm bin. Heat mats and aquarium heat elements can be used as they are and don’t need any alterations. Spot heating inside the worm farm gives worms the space to wiggle as close or as far away as they find comfortable. It’s a good way to keep worms not just alive but also more active during winter.

6. Design and build a winter-proof worm farm

There are several design possibilities to keep your worm farm going through the winter. If you have outdoor space here are some possibilities. 

Go Large: Large Worm Farm Box.

Build a large box or recycle a high-raised bed. It should be at least 2 foot in length and width, the wider the better, depending on how much food scraps you will accumulate over winter. Make sure it is well protected against rodents at the bottom but can release excess leachate. A fine wire mesh is a good option.

Think ahead how to empty this when composted. Most people remove one side of the box to remove the finished compost. 

Fill with a 2-3 inch thick layer of carbon rich bedding material.
6 months aged horse manure, autumn leaves, compost,  or if you have no access to natural material use soaked shredded cardboard. Ideally you would start this over summer, early autumn to give worms a chance to move in and multiply.

Bear in mind that a box of that size will need loads more worms to get it going. Add food as and when it becomes available. Also, add about as much carbon rich material as you add fresh nitrogen plant waste. 

A large worm box like this is unlikely to freeze through in most areas and worms will be able to crawl deeper to safe levels when the frost hits the bin.

Build a Hot Compost with ‘Cold Compost’ underneath

Here is an example from Alberta where the ground freezes deep and still a worm population is being kept alive season after season.

Start with mulching through the summer (careful with this one if you have a slug problem). In winter a hot compost provides heat and, once it cools down, a source of food for worms. 

Add an electric heatmat to your outdoor bin

If you don’t have a natural source of heat or one that’s there anyway, for example from an air vent or a similar, a seedlings mat could be a good option even for a large outdoor bin, just to keep worms more active and keep turning food scraps into vermicastings. 

Conclusion

Wherever you are, with a bit of planning ahead worm composting in winter is possible. Keeping your worm team alive and having fresh worm castings ready for spring either for your own use or to give away to friends is well worth the extra little effort.

Leave a Comment

Your email address will not be published. Required fields are marked *