Dozens of seedlings in my compost tumbler, should I worry?

Howdy folks, I'm sure this has been discussed here before but even advanced googling of the site is not finding it, so please forgive a repeat topic!

Thing is, I'm getting dozens and dozens of seedlings in my compost tumbler this summer.  In autumn I used to fill the whole tumbler in one go and wait a month for it to break down, then repeat the process.  But I don't need compost as quickly as I did back then, so I'm able to be more relaxed about it this summer.  I'm adding about a quarter of a compartment once a week, and once the compartment is full I'll then leave it for a month before removing to the storage bin.  Meanwhile repeating the process on the other compartment.

Consequence is, of course, that my temps are much lower because my volume isn't yet big enough.  The max I've had so far is only 102°F, and I only saw that on one morning.  The other days this week it's been down in the low 90s.

I had a good old manual stir this morning and found dozens and dozens of little seedlings.  Should I worry about them?  My tumbler volumes aren't big enough to actually sanitise compost: even my hottest batch in autumn averaged only around 110° and that only for 7-10 days.  So, even once the compartment is full in a week's time I doubt it's going to get truly high.  Are these seedlings going to continue living in my lovely rich nutrients unless I get them all out???

KiwiSFGnewbie wrote:Consequence is, of course, that my temps are much lower because my volume isn't yet big enough.  The max I've had so far is only 102°F, and I only saw that on one morning.  The other days this week it's been down in the low 90s.

I had a good old manual stir this morning and found dozens and dozens of little seedlings.  Should I worry about them?  My tumbler volumes aren't big enough to actually sanitise compost: even my hottest batch in autumn averaged only around 110° and that only for 7-10 days.  So, even once the compartment is full in a week's time I doubt it's going to get truly high.  Are these seedlings going to continue living in my lovely rich nutrients unless I get them all out???

Last question first: No, let them die naturally and compost.

First question: No, they won't hurt anything, and they will eventually compost with the other material.

Those seedlings will die and be composted once the compost reaches a temp of 140 or higher. You need to determine if the problem is that there is not enough brown, or not enough green in the tumbler to cause the heat to happen, then correct it accordingly. Remember that too high a C:N ratio will cause prolonged composting duration, while too much nitrogen will cause rotting instead of composting. The fact that you are seeing seedlings, though, indicates that the C:N ratio is too high resulting in cool damp matter for the seeds to germinate in. If that is the case, add some nitrogen such a alfalfa meal, coffee grounds, or manure.

If you do not already have a similar book, try to get one similar to The Rodale Book of Composting.

Many thanks for this, OG

To be honest I don't know whether to regard it as good news or bad!  On the one hand it's a relief that maybe I won't have to pick through all that material and pull out all the tiny seedlings in it -- on the other, "all" I have to do is get the temperature high enough.....which never happened to my autumn batches

Back then I did actually try to put together a "recipe" using the excellent instructions for calculating C:N volumes in a thread here, I think you wrote it?  I'm a detail person and this sort of thing is right up my alley.  But I got very confused because of all the different C and N values out there on the web (for the same ingredients).  Also, since I was using a food processor to get my food scraps scraps chopped up nice and tiny (because I was in a hurry) my volumes were going to be different from what is normal for food scraps and I really wasn't sure how to adjust for that.

So, I ended up doing it basically by nose and moisture level.  My third and final autumn batch was a ratio of 38 greens to 51 browns (sawdust and shredded leaves) and this one took only about a week for the smell to come sweet but the temperature was only above 100°F for 9 days before reducing quickly to range 60-75.  By then we were in winter with ambient temps around 50, but then I remember you saying you get sanitising temperatures in your tumbler even in the depths of your winter!  So, .....?????

This summer I'm manually chopping the food scraps, so in bigger chunks than the food processor makes.  Because the mixture is therefore drier, I only add an equal volume of sawdust with them but then have been adding extra most mornings, to get it up to around 1:2 greens to browns by the end of the 7 day period before starting the process all over again.

I've also been adding coffee (again, at a 1:1 ratio with sawdust) and can certainly add more, I have access to essentially as much as I want, but had been keeping the volume fairly small -- just one quarter of my greens.  (I saw yesterday that you use a fair amount of it)  Could try adding a goodly amount (without more sawdust) and see what happens?  But I thought we should be aiming for 1:2 or 1:3 greens to browns?

Good news: my local library has the Rodale book, and no-one else has it out, so I ought to be able to get hold of it within the week

But I really do wonder if this tumbler is simply too small.  Each compartment is only about 4.25 cubic feet, after all.

Which raises the question: if I can't kill these seedlings, am I going to need to pick them out?? (she says with desperate hope the answer is not Yes!!)

KiwiSFGnewbie wrote:I've also been adding coffee (again, at a 1:1 ratio with sawdust) and can certainly add more, I have access to essentially as much as I want, but had been keeping the volume fairly small -- just one quarter of my greens.  (I saw yesterday that you use a fair amount of it)  Could try adding a goodly amount (without more sawdust) and see what happens?  But I thought we should be aiming for 1:2 or 1:3 greens to browns?

Typically you want a higher C:N ratio, since the carbon provides the carbohydrates that microbes need for the energy to compost the material, but the nitrogen provides the growth of the microbial populations. As you noted, though, achieving that ratio is more of an art than a science. (For scientific review, check out this document from Cornell: https://compost.css.cornell.edu/chemistry.html).

Coffee grounds are a difficult to understand in composting due to many misconceptions. Many sites will tell you, for example, that you should never use more than 10% of the total volume with coffee grounds, but never explain why. I have Composted 100% coffee grounds (with the filters), and had excellent compost. Coffee grounds have a C:N ratio of 20:1, which is very close to the desired 30:1 ratio, so including the coffee filters for carbon makes a good balance of C:N to compost. If you are adding carbon at an equal rate of coffee grounds, you are adding way too much carbon -- sawdust has a C:N ratio of 500:1, and the coffee grounds are 20:1, so an equal amount of each would result in a C:N ratio of 520:2, or 260:1 -- way out of balance, and it will never provide enough nitrogen to heat the compost.

Good news: my local library has the Rodale book, and no-one else has it out, so I ought to be able to get hold of it within the week

But I really do wonder if this tumbler is simply too small.  Each compartment is only about 4.25 cubic feet, after all.

You will enjoy that book.

The size if probably not an issue. My two Jora JK-270 compost tumblers each have two bins of 4.75 cu ft each, and when a bin is filled it quickly reaches a high temp.

Which raises the question: if I can't kill these seedlings, am I going to need to pick them out?? (she says with desperate hope the answer is not Yes!!)

No, that would not be necessary. Even with cold composting you will find seedlings sprouting - some of our best cucumbers and winter squash came from seedlings that sprouted in the cold compost bin and spread over everywhere. Last year we had a cherry tomato that came up in the small area between the two boards of the pallet, and it grew out the top of the pallet to produce some great tomatoes.

As the compost is turned, the seedlings will die and be composted.

OhioGardener wrote:

KiwiSFGnewbie wrote:I've also been adding coffee (again, at a 1:1 ratio with sawdust) and can certainly add more [...]  But I thought we should be aiming for 1:2 or 1:3 greens to browns?

Typically you want a higher C:N ratio, since the carbon provides the carbohydrates that microbes need for the energy to compost the material, but the nitrogen provides the growth of the microbial populations. As you noted, though, achieving that ratio is more of an art than a science. (For scientific review, check out this document from Cornell: https://compost.css.cornell.edu/chemistry.html).

What a great series of documents!  I've had a moderate look and will work through the rather dense material slowly -- it gives me a great place to start, it's clear I need to refine my notion of compost "recipes".  When I gave up trying to calculate C:N I decided to just go with greens:browns since the browns are so much higher in C, really I was just trying to fake it and then adjusting via smell and moisture as time went by.

I have Composted 100% coffee grounds (with the filters), and had excellent compost. Coffee grounds have a C:N ratio of 20:1, which is very close to the desired 30:1 ratio, so including the coffee filters for carbon makes a good balance of C:N to compost. If you are adding carbon at an equal rate of coffee grounds, you are adding way too much carbon -- sawdust has a C:N ratio of 500:1, and the coffee grounds are 20:1, so an equal amount of each would result in a C:N ratio of 520:2, or 260:1 -- way out of balance, and it will never provide enough nitrogen to heat the compost.

Oh!   Oops.....  (well, I guess this stoobie mistake can maybe serve as useful info for other newbies out there!)  Perhaps I should be congratulating my microbes for doing as well as they are

The size if probably not an issue. My two Jora JK-270 compost tumblers each have two bins of 4.75 cu ft each, and when a bin is filled it quickly reaches a high temp.

Oh, OK -- I had a feeling (from last autum) that yours was a lot bigger than mine.  This is really motivating, can't wait to start seeing some truly high temps  

As the compost is turned, the seedlings will die and be composted.

Thank goodness for that!  Thanks, OG

KiwiSFGnewbie wrote:What a great series of documents!  I've had a moderate look and will work through the rather dense material slowly -- it gives me a great place to start, it's clear I need to refine my notion of compost "recipes". 

Hopefully you were able to download the PDF file, "Composting to Reduce the Waste Stream - A Guide to Small Scale Food and Yard Waste Composting". It offers a lot of good info on home composting, including suggestions on building home compost bins. If you didn't see the link to download it, it can be downloaded here:

 https://ecommons.cornell.edu/bitstreams/f59e9ba5-2321-4774-9d0d-9a4f02ffaf05/download

One of my favorite quotes in that paper is this:

I used to use this calculator to get the ratios decent. Large volumes heat up and hold temps better than smaller volumes.
Conversely, temps over 160*F are not healthy. When mine hit that number, I had to frantically dismantle for thorough turning and letting the steam out. Somewhere around 140-150 throughout the material is nice, but it means mixing to make sure that all parts get the seed and pathogen killing temps.

Kiwi, at least you know you can make compost in your bin. Now just to fine turn the tumbler.

https://www.klickitatcounty.org/DocumentCenter/View/3523/Compost-Calculator

When I composted, I would collect culls from the evening farmer's market.  Then spend a few late-night hours chopping the produce to be ready by morning.  I found the sweet spot, or rather the sweet size, after thinking everything had to be diced.  If this looks like a lot, keep in mind my bin was 3'x3'x3'.  The rest of the volume was dry leaves and mowed bedding straw, with a few bags of Starbucks coffee grounds and 33 gallons of horse poop.  In hind sight, I should have aimed for 30:1 ratio and not 25:1.  

sanderson wrote:When I composted, I would collect culls from the evening farmer's market. 

Great way to get some extra compost material!  I pick up bucketfuls of fruit/vegetable pulp from a local juice bar, which is about the same thing except it is already chopped into small pieces.

OhioGardener wrote:Hopefully you were able to download the PDF file, "Composting to Reduce the Waste Stream - A Guide to Small Scale Food and Yard Waste Composting". It offers a lot of good info on home composting, including suggestions on building home compost bins. If you didn't see the link to download it, it can be downloaded here:

 https://ecommons.cornell.edu/bitstreams/f59e9ba5-2321-4774-9d0d-9a4f02ffaf05/download

Hey thank you, I didn't notice that link!  Will trawl through it in my 'copious' spare time   And what a comforting quote, to remind us all that "compost happens"

sanderson wrote:I used to use this calculator to get the ratios decent.

https://www.klickitatcounty.org/DocumentCenter/View/3523/Compost-Calculator

Hey, this is great!  And as a programmer I'm easily able to adapt the code and add a bigger ingredient choice and even the ability to have more than 4 ingredients in the mix.  I can provide it to anyone here in a simple .HTML file which you can double-click to run in your browser.

I've just written to them to ask permission, and once I hear from them I'll get back to you folks.

sanderson wrote:I found the sweet spot, or rather the sweet size, after thinking everything had to be diced. 

Wow, those pieces look way bigger than what I've been doing this summer -- I'm obviously putting far too much effort into this!  Thanks for the info, sanderson

Ohio Gardener wrote:I pick up bucketfuls of fruit/vegetable pulp from a local juice bar, which is about the same thing except it is already chopped into small pieces.

Ah yes, now I remember seeing you mention this in autumn, but at the time thanks to my food processor I didn't need the idea -- will start haunting the local ones, great idea

Coo-ool.  I have a bucket right now at the local juice bar, being filled with lovely pulp for my tumbler   Plus some grass clippings drying in the wheel barrow (so they hopefully won't clump).  Looking forward to some higher temps RSN!

So it's been two and a half weeks since I started working on the C:N ratio of my tumbler, and I've deliberately been waiting until I was sure the improvement in temperatures was real.  Last year I saw temps in the 115-130°F range, but only fleetingly.  However, both compartments have now been above 120°F for 7 days now -- highest I've seen is 135° -- and yes, we're not at 140° but surely they're good enough?  I never put plants of any type in the compost, so weed seeds aren't an issue for me and neither is killing off disease pathogens.

I ended up moving half the material from the nearly-full and not-hot-enough compartment, into the nearly-empty one.  Then the addition of fruit pulp from the local juice bar, and coffee grounds, got both sides cooking nicely as above.

My ratios are 1:60 and 1:82 -- again, yes, they're not at the ideal figures, but frankly I can't imagine how to get them there.  The material is already too wet; I'm adding a handful of sawdust per day, mindful of how potent it is.  I was looking for other dry ingredients I could add, but they all seem to have carbon levels about the same as sawdust, so really there didn't seem much point.  From the temperatures it's clear that even at these ratios there's an awful lot of microbial activity going on, and I sure haven't seen any seedlings for quite a while!

One thing I am seeing is larvae, I suspect from the black soldier fly.  I've seen some crawling in through the air vents, so yesterday I taped some tulle over them and hopefully that'll solve that.  I can't permanently attach any sort of screen, since the vents are on the walls of the tumbler, not the ends as with the Jora, so need to be cleared every few days.  I don't exactly enjoy seeing creepie crawlies on the top of my compost, but I'm reminding myself that as the Rodale book says (which I am making my way through currently), they're physical decomposers and are munching up my fruit pulp for me!  I'm not normally squeamish but these puppies are on the hairy edge of being just too...well...ookie for me.  If I call them larvae to myself I can handle it better than maggots!!

Their life cycle seems pretty quick, so my hope is that by the time I unload the tumbler they'll have mostly hatched and can fly away??  Or perhaps if I spread it on the lawn and let it dry a bit, they'll die??

So, all in all the tumbler is going much better and I'm looking forward to being able to start a batch with something much nearer to a proper C:N ratio, in about a month's time!

KiwiSFGnewbie wrote:One thing I am seeing is larvae, I suspect from the black soldier fly.  I've seen some crawling in through the air vents, so yesterday I taped some tulle over them and hopefully that'll solve that.  I can't permanently attach any sort of screen, since the vents are on the walls of the tumbler, not the ends as with the Jora, so need to be cleared every few days.  I don't exactly enjoy seeing creepie crawlies on the top of my compost, but I'm reminding myself that as the Rodale book says (which I am making my way through currently), they're physical decomposers and are munching up my fruit pulp for me!  I'm not normally squeamish but these puppies are on the hairy edge of being just too...well...ookie for me.  If I call them larvae to myself I can handle it better than maggots!!

Their life cycle seems pretty quick, so my hope is that by the time I unload the tumbler they'll have mostly hatched and can fly away??  Or perhaps if I spread it on the lawn and let it dry a bit, they'll die??

Yes, those are Black Soldier Fly larva, and they are your friend. They are there only because they have found food that is spoiling rather than composting, and they are cleaning it up for you. The frass from the larva is great food for the microbes needed to break down the compost for you. Rather than blocking them, or trying to remove them, let them do their work. They are not harmful in any way, and help enrich the compost.  As your composting techniques improve you will see fewer and fewer of the Black Soldier Flies visiting your compost.

OhioGardener wrote:Yes, those are Black Soldier Fly larva, and they are your friend. They are there only because they have found food that is spoiling rather than composting, and they are cleaning it up for you. The frass from the larva is great food for the microbes needed to break down the compost for you. Rather than blocking them, or trying to remove them, let them do their work. They are not harmful in any way, and help enrich the compost.  As your composting techniques improve you will see fewer and fewer of the Black Soldier Flies visiting your compost.

Oh!   Maybe they're there because of the clumps of fruit pulp?  The first two weeks I tried to 'crumble' it in by hand, but with material that wet there's only so much you can do.  This week I manually mixed it with coffee grounds (which I've always pre-crumbled) before adding, and got a much finer mixture.

I'm still finding clumps which I assume are left over from the first two weeks, which I crumble and then cover with other material.  Hopefully this will reduce in time.

I shall try to view the larvae as a positive

The BSF loves fruit and kinds of other stuff.  I thought I would grow some little red compost wigglers and actually ended up raising a couple summers worth of BSF.

Only fruit pits and frass left behind.


How mom got into the box in the first place and how the new flies got out. Climbing tubes are recommended if raising them intentionally.


Open bottom setup originally for the little red wigglers.


https://www.bing.com/videos/riverview/relatedvideo?q=black+soldier+fly+larvae+eating+a+hamburger&mid=9004DA35A54157BF029A9004DA35A54157BF029A&FORM=VIRE

  Man, they're thorough, aren't they?!  (reminds me of how doctors use maggots to remove gangrenous flesh)  I love that they leave behind much more of the hamburger than the pear!

sanderson wrote:The BSF loves fruit and kinds of other stuff.  I thought I would grow some little red compost wigglers and actually ended up raising a couple summers worth of BSF.

Only fruit pits and frass left behind.

Back before the windstorm took out our apple tree, it was always fun to watch the BSF larva and the bees/hornets compete for the bruised fruit on the ground. The bees/hornets were trying to get sugar from the fruit, while the BSF larva were busy eating the whole thing. Neither one seemed to bother the other one, though. The adult BSF does not feed, and has no capability to bite or sting. 

Check the post I just put in titled,  "Black Soldier Fly Composting":

https://squarefoot.forumotion.com/t24046-black-soldier-fly-composting#309201

Wow!  Who'd a thunk it, using larvae for composting!  Sometimes the world of gardening sure throws up some weird stuff, to this newbie