Small Trenches and Coffee Grounds

A couple of questions from Kathleen:

What’s the smallest trench that you can use for worms? I have a number of holes dug by my dogs that I would like to fill and be useful at the same time. I can do a little digging to enlarge but physically not able to do much. Is there any hope for the mine field in my back yard?

I’ve been doing a lot of web searching and remember seeing something about “aged” coffee grounds. Is it necessary to age them before adding them to the bin, and, if so, how do I go about aging them?

Hi Kathleen,
I don’t know if I’d say that there is a specific “minimum size” for vermicomposting trenches and pits – but there are certainly some important considerations. Likely the primary factor of importance is your local climate. Do you live in an area that gets really hot? Really cold? Really wet? Really dry? If you deal with one or more of these extremes, you’ll likely need to put a little more time and effort (and thought) into the construction of your pit/trench.

In most cases, it’s likely going to be a good idea to dig down at least a foot – but if you if you plan to add an above-ground element (eg windrow, backyard composter etc) and/or add lots of protective materials you may be able to get away with less. Straw and leaves are great materials (although the latter tends to blow away so best if sitting under a layer of straw or some other type of cover), and even something like an old carpet or blanket (although not the most aesthetically pleasing) can work as well.

In locations with really hot summers and/or really cold winters, you’ll almost certainly need trenches/pits with greater depth (2-3 feet), plus lots of protective materials over top.

My hunch is that your dogs aren’t likely digging 1 ft+ holes for you, so you may need to get someone (aside from your dogs – lol) to help out. But if you live in a location with pretty moderate weather all year, simply adding protective materials over top may do the trick!

As for coffee grounds…

While it’s not vitally important for grounds to be aged before adding them to a vermicomposting system (especially in moderation), there is an advantage to doing so. As is the case with a lot of waste materials, aging provides the time/opportunity for a community of microbes to become established on the grounds. This in turn makes them more appealing to the worms.

My suggestion for aging them would be to simply mix them with other compostable kitchen wastes and (ideally) some bedding materials, and then leave them to sit in some sort of ventilated container (that still helps them to stay fairly moist) for a week or two. Alternatively, you might try a more active “pre-composting” stage instead, using something like a compost tumbler or some other large composting system (this might be more applicable if you had lots of coffee grounds to deal with). Again – same idea as the aging. You definitely should mix the grounds with some other materials, including some carbon-rich bedding.

If your mix ends up smelling foul – do NOT add it to your vermicomposting system (at least not if you are using a small bin of any sort). Simply add some more bedding materials and take some steps to insure better aeration.

Hope this helps!

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    • sue
    • April 1, 2013

    I am not sure of what volume of coffee grounds you are talking about in the above article on coffee grounds and vermicomposting. I have used on average 2 persons’ supply of coffee grounds per day in my enclosed worm bins for about 20 years now, and the worms seem to thrive, there has only been anaerobic odor once (I think due to a huge input of cruciform vegetable remains at the time). There is a modicum of vegetable and fruit waste in the bin also, and some cardboard. I live in San Francisco, so the bins tend not to get dry or overheated. Plants do well with applications of both the worm compost and the compost tea.
    My cool maggot experience was with the rattail maggot (the larva of the drone fly, a harmless pollinator) whose “tail” is really a breathing tube for when the maggots are submerged as they were in my worm bin at the time. These were mainly only seen when something had happened (storm; theft) to keep the lid off for several days.

    • Bentley
    • April 2, 2013

    That’s really interesting, Sue!
    I would think that that quantity of grounds would pile up fairly quickly (but perhaps you have multiple bins going at once).
    I’ve had good success with coffee grounds added in moderation to enclosed plastic bins as well. It’s much more of a pain-in-the-neck, in my experience, when added to really well ventilated systems and/or when a huge amount is added at once.

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