Vermicompost Vitality

Here’s a question from Corey:

Thanks in advance for all your work and info! It’s truly
appriciated. I have what may seem to be a silly question, but here it
goes : Does harvested vermicompost lose its virality/vitality over
time during storage? My concern is that harvested casings during the
off growing season would sit unused for a few cold months before being
incorporated into the garden-may lose its potency. Just a thought –
but it never hurts to ask –

thank you!

Corey in PA

Hi Corey – that is actually an excellent question (which is why I decided to post it on the blog). The short answer is definitely “yes” – but there are lots of factors involved (and potential scenarios) here so I certainly won’t leave it at that!

Using high quality vermicompost soon after it is harvested will almost certainly provide you with more benefits than if you use the material after it’s been sitting for 5 years. Unlike a fine wine, vermicompost doesn’t really improve with age (haha). A short ‘sitting’ period can definitely be advantageous in some situations however. You’ll notice I mentioned “high quality vermicompost” – well the stuff that often comes out of the bottom of a ‘Rubbermaid’ tub type of worm bin generally doesn’t fall into this category, in my humble opinion. This is especially true if there are no drainage holes.

This material will very often be overly wet, with anaerobic zones – and may in fact not even be finished vermicompost. Material like this should allowed to sit someplace where excess moisture can drain away and there is plenty of air flow to aid with the drying process and provide plenty of oxygen to allow the aerobic microbes to finish the job.

In the case of the really good quality stuff – material that is harvested from some type of flow-through system for example – the storage stage isn’t really needed, and it will likely be at its peak for beneficial microbial activity. If it is left to sit, microbes will gradually start to die off and/or become inactive since there won’t be all that much ‘food’ value left – it will be rich in humus and thus highly stabilized.

Now don’t get me wrong here – if we take the scenario you mentioned, in all honesty I don’t think you will lose a signficant amount of the potency during the winter months of storage – especially not if you are able to store the material in a cool, relatively dry (don’t let it completely dry out though) spot. Perhaps in your basement somewhere? The cool temperatures (and low moisture content) will slow down the microbial activity, thus also slowing down the ‘aging’ of the vermicompost.

You might also think about doing a gradual freezing of the material. While I probably wouldn’t recommend simply throwing a bag of fresh vermicompost straight into a chest freezer, if you start storing the material in an outdoor shed in the fall, my hunch is that you’ll get a higher percentage of microbes becoming inactive (forming resistant cysts), rather than being quickly killed.

Perhaps you have a spare fridge somewhere? I would think that this could be a good way keep your material fairly fresh as well.

By the way – some other ways you can really speed of the decline of your vermicompost include letting it sit out in the rain and/or hot summer sun. Precipitation is basically just going to wash away a lot of the ‘good stuff’, while the hot sun will likely just end up sterilizing the material.

Anyway – I hope this helps, Corey! Thanks for the great question.

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    • Uncle Jim's Red Wiggler Farm
    • August 14, 2009

    Another thought. Worm Tea (liquid collected from fresh worm castings) is only good maybe a day or so after collecting it. If you buy it bottled or store it, it really loses it power quickly.

    • Bob Packard
    • August 14, 2009

    Hi Bentley, I’d like to here what your friends at Worm Power have to say about this. I bought 60 each 30 pound bags of castings about a year ago and have been using them all along to fertize plants, trees and vegetables and everything appears to be thriving nicely here. I also use them for teas. I bought the large amount to save on freight.

    Also we have been in a drought here for over a year and I fear that the chances of burning plants with chemicals is even more reason to stick with castings and worm compost.

    • Bentley
    • August 14, 2009

    Glad you chimed in, Bob – that’s exactly it. When vermicompost/castings ARE stored properly, the shelf life is going to be much longer. I would still argue that the best castings are the ones that have been recently harvested – but it could be many months or years (assuming good storage) before the beneficial properties are reduced substantially.

    And of course, Jim is definitely right about the worm tea – that is a whole other matter altogether. I still have no clue how Terracycle does it – but I suspect their product simply isn’t as good as a fresh high quality brew of worm tea.

    • Heather
    • August 15, 2009

    My thoughts are that bottled vermi-tea might have same fertilizer impact (as fresh), but not the wonderful, impact of the beneficial organisms. No oxygen, no life.

    • allochthon
    • August 18, 2009

    On a local gardening list, there was an extensive discussion about freezing vermicompost to kill off the worms and cocoons. The worry was that fresh compost would allow the worms out into the local environment, where the non-native worms can do a fair amount of damage (

    That site states that red wrigglers can’t (yet) survive a Minnesota winter, but with a litle assistance they certainly can, as you’ve proven (such a cool project!)

    Have you given much thought to this, with your worm trenches and winter composting?

    • Bentley
    • August 19, 2009

    Hi Allochthon,
    I live in a farming region where Red Worms are relatively widespread (in comparison to northern regions). I am still a little skeptical about the notion of this species causing issues in forests to be totally honest – I have yet to find a population of Red Worms in forest litter. I find them around my property in funny locations, but they only seem to actually thrive in areas with lots of rich organic matter (such as manure, food waste etc).
    I’ve read that Canadian Nightcrawlers can cause serious damage in forests, and this makes a lot more sense since they live in soil and feed on materials like leaf litter (they end up greatly speeding up decomposition of litter and overall cycling of nutrients).

    Anyway, I am far from an expert on this particular issue, but I do know that the concern with non-native worms relates to northern forests (Minnesota is actually quite a bit north of me even though I am in Canada).

    There are likely some Red Worms living in various locations on our suburban block thanks to my vermi-activities, but I am not worried that they’ve invaded and are taking over our local forests.

    You HAVE piqued my curiosity though – there is a forest down the street from me. I’d be interested to see if I could find any Red Worms there.

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