The Vermicomposting Trench – Part II

Worm Composting Trench
My vermicomposting trench has helped me grow big, healthy plants this season.

I think I provided a decent overview of my vermicomposting trench system with my first post, but I thought it might not be a bad idea to add a follow-up – this way I can fill in some of the gaps and provide a general update on my progress.

As you can probably tell from the image above, my plants are continuing to thrive thanks to their close proximity to the trench (no I don’t have scientific proof to back it up – but let’s just call it a ‘hunch’ on my part! haha). As you may recall, I’ve added no inorganic fertilizers this year, yet my tomato plants are quite a bit bigger than the maximum size reached by my (fertilized) plants last year. I’m looking forward to seeing how my crop turns out – I’ve done absolutely nothing with the plants other than support them (after they started falling over), so I’m not sure that the quality of the tomatoes will be as good as it could have been, but we shall see. There are loads of really nice looking green tomatoes now, so I’m sure there will be at least a few good ones harvested.

My zucchinis have certainly been growing like crazy as of late. We’ve been enjoying some of them on the BBQ already – delicious! I can’t get over how quickly the plants are replacing the ones being harvested, and just how quickly the individual zucchinis reach a good harvesting size! I think just for fun I may let one of them continue to grow, just to see how big it will get!

There were some great questions asked after I wrote my last trench post, and while I did do my best to answer them in the comments section of that post, I thought it would be beneficial to include some of those topics in this post as well. Here then are some of the things people have been curious about:

Heat / Cold – One of the great things about an in-ground vermicomposting system is that it is protected from weather extremes. In comparison to an above-ground worm bin for example, it will generally be easier to keep temperatures cool enough during the hot summer months, and be able to prevent it from freezing during winter months.

I’ve definitely been having a lot more trouble with overheating in my large outdoor worm bin than in my trenches. That being said, when you first set up the trench (and add a considerable amount of organic waste at once), you will need to be more careful – at least if you are planning to add composting worms. You are probably better off waiting for a week or more, and even then you should take temperature readings to make sure it’s not too hot. If you are adding mostly ‘brown’ (carbon-rich materials), or are building the trench in the early spring or fall (when cool), this likely won’t be as much of an issue.

Someone asked about issues associated with being in direct sunlight (fairly important for the success of a vegetable garden). While I suspect that my approach just isn’t feasible in some locations where it is very hot and dry, I’ve personally found that keeping a nice thick layer of straw (and other ‘brown’ organic matter) really seems to help keep the moisture in and the heat out.

I can’t say for sure how well the system will respond to really cold weather. I suspect my larger sandbox trench will stay quite warm during winter months (assuming I add lots of food waste and bedding materials) – not so sure that the other trenches are large enough to hold significant heat. Either way, I’m sure a lot of the worms will still survive the winter (I’ll definitely add lots of straw and leaves over top before the snow starts flying.

Adding Materials to Trench – Depending on the quantity of wastes you have access to on an ongoing basis, you’ll likely want to go with either a ‘continuous’ or ‘batch’ approach. I suspect that for most regular homeowners the latter approach will make the most sense, since they won’t have a constant supply of organic wastes that need to be dealt with. In this case you would simply stockpile your materials, build your trench (likely in the fall or spring), then simply let it sit and compost without further additions. Or perhaps you would simply add more materials (lawn clippings, weeds etc) as they became available.

In my case, it’s been important for my trenches to be ‘continuous’ systems due to the large amount of food waste I’m receiving daily from the restaurant. When treating your trench as a continuous system, it becomes even more important to optimize your methods. As I’ve discovered, it is quite important to chop up materials fairly well before adding them to the trench. Out of curiosity I tried adding whole broccoli stalks (one of my most abundant waste materials) to my main trench. It was amazing how much more slowly they decomposed in comparison with those chopped up with a spade beforehand.

All I’ve been doing when adding new materials is simply pulling back the thick layer of straw (and grass clippings), adding a layer of waste 2-4 inches thick, then covering back up. On occasion I’ve been adding some egg carton cardboard underneath the food waste to help provide more structure for the worms and help to balance the C:N somewhat. Eventually, as the overall level of materials in the trench sinks, each top layer of straw becomes the base upon which new food waste is added, with a new thick layer of straw added over top. Straw is an excellent material to use if you are planning to have worms in your system – Red Wigglers just seem to love crawling around in and munching on moist rotting straw. When there is rotting food waste in there as well, it becomes an excellent combination of habitat and food source – not unlike a well-aged manure and straw mix.

Moisture in the Trench – As with any composting system, moisture is certainly an important consideration. This is especially true if you live in an area with really heavy clay soils and/or abundant rainfall. Too much moisture in the trench can create anaerobic conditions and slow down the decomposition process – something that it probably unavoidable near the bottom of your trench due to the lack of air flow. Situating your trench directly beside water loving crops like tomatoes and various members of the cucumber family should certainly help, especially during dry summer months. The composting worms themselves should also help to aerate the system somewhat via their movement within the decomposing organic matter.

As I discovered, things can really slow down during periods of consistently wet weather – I’m sure this wouldn’t have been so noticeable if my worm population in the trench at the time had been higher. I will definitely be interested to see how the system performs once the wet fall weather arrives. I should have a lot more worms by then, but I won’t have the jungle of plants and hot weather I have now so it might be a bit more challenging – I suspect the trench will become more of a windrow since the level of materials will likely continue to rise above the ground.

Anyway, looks like this follow-up post is getting a little longer than I had planned to make it – but of course, I still don’t feel like I’ve covered the topic completely. Oh well – I’m sure I’ll provide more information in the video I’m going to put together, and will almost certainly provide a few more updates over the next couple months.

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    • Roxanne
    • December 16, 2008

    Hi Bentley,

    I’m new to your site and I’m loving it. Any updates on your trenches? Are you still actively maintaining them?
    After reading about your ingenious idea I decided to trench around my vegetable garden. I live in TX on clay soil so digging 2 feet down is definitely not happening but I’ll try my best!

    • Bentley
    • December 18, 2008

    Good question, Roxanne. A final update is LONG overdue. I’ll be writing a post about it when I get the chance. Long story short – I don’t have any active trenches at the moment – have been putting all my focus on a single (large) winter worm bed.

    • Mary
    • April 6, 2009

    Hi Bentley,
    I just wanted to thank you for your advise on how to layer my trench so that I would have worms this year. I went out yesterday to finally peel back some of the layers of straw, cardboard and leaves to find…..WORMS!
    They looked fat, healthy and numerous. I am absolutely thrilled, even my family was happy for me!! (That’s all they’ve been hearing about for the past 4 months).


    • antuan
    • June 23, 2011

    I’m looking at switching to in-ground systems to raise my worms/vermicompost etc. I was thinking of just digging down say 3ft and making a pit 3×6 in a shady area -I live in No California, hot summers but have lots of cardboard/straw and egg cartons from cricket holders to dispose of weekly…Whats your thoughts? I’ve got a ton of castings and lots of little babies with no homes and tired of the bin system

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