Things you can compost!
| Materials | Carbon or Nitrogen | Details |
|---|---|---|
| Alfalfa meal and hay | Carbon | Shredding or chopping it up will help it break down quicker |
| Algae, seaweed and lake moss |
Nitrogen
|
Good source of nutrients and minerals. |
| Apple pomace (cider press waste) | Nitrogen | If dried use as a carbon |
| Ashes (wood, not coal) |
Neutral
|
Use only wood ashes since coal ashes can be toxic to plants. Use sparingly as a pest deterant. |
| Banana peels | Nitrogen | Shredding or chopping it up will help it break down quicker |
| Beverages, kitchen rinse water |
Neutral
|
Help keep the pile moist, but don’t over do it. |
| Buckwheat straw or hulls | Carbon | Shredding or chopping it up will help it break down quicker |
| Cardboard |
Carbon
|
If you have lots of this, consider recycling it. Otherwise, shred into small pieces in pile. |
| Cat litter (unused!) | Carbon | Ugh..make sure its unused |
| Clover | Nitrogen | Add it for a bit of luck! |
| Cocoa hulls | Carbon | Shredding or chopping it up will help it break down quicker |
| Coffee grounds (and filters) |
Nitrogen
|
Great source of nitrogen and worms love coffee grounds! The filter will break down so add it too! |
| Cornstalks, corn cobs | Carbon | A little tricky, so shred and/or break down and mix well into pile. |
| Cotton Bur | Nitrogen | Great to use to jump start your pile or warm it up |
| Cowpeas | Nitrogen | Add them if you got them! |
| Dog food |
Nitrogen
|
Best if not a meat based dog food |
| Dryer lint |
Carbon
|
Yum, lint. Make sure you moisten it a little before you add it. |
| Eelgrass | Nitrogen | If dry use as a carbon |
| Egg shells |
Neutral
|
These break down slowly, so make sure to crush these before adding. |
| Feathers |
Nitrogen
|
Slow to break down, shred if possible to speed up process |
| Flowers | Nitrogen | Green use as Nitrogen, dried use as carbon |
| Fruit peels (not limes) | Nitrogen | Best if you cut them up to small pieces |
| Grape pomace (winery waste) | Carbon | When dried and shredded best used as a carbon |
| Green Grass clippings |
Nitrogen
|
When green can be used as a Nitrogen |
| Dried Grass clippings |
Carbon
|
Make sure they are not too wet and mix with dry leaves for best results. |
| Hair |
Nitrogen
|
Good source of nitrogen. Make sure you scatter, so it doesn’t clump. |
| Hay |
Nitrogen
|
The best kind is hay that is not suitable for livestock and is starting to decay on its own. Make sure it is dry and weathered. |
| Hedge Clippings | Carbon | Shredding or chopping it up will help it break down quicker |
| Hops (brewery waste) | Carbon | When dried and shredded best used as a carbon |
| Kelp (seaweed) | Carbon | Good source of potassium (perfect for growing potatoes!). Use sparingly or sprinkle kelp meal in to get your pile cooking. |
| Leather (leather waste) |
Nitrogen
|
Shredding or chopping it up will help it break down quicker |
| Leaves |
Carbon
|
Shredding or chopping it up will help it break down quicker |
| Manure from herbivores (cow, horse, pig, sheep, chicken, rabbit) |
Nitrogen
|
Best if known to come from a herbivore |
| Newspaper |
Carbon
|
Shredding or chopping will help it break down quicker |
| Nut shells | Carbon | Shredding or chopping will help it break down quicker |
| Oak leaves |
Carbon
|
Shredding or chopping will help it break down quicker |
| Oat straw | Carbon | Shredding or chopping will help it break down quicker |
| Sawdust and wood shavings |
Carbon
|
Preferably not from kiln-dried wood |
| Paper | Carbon | Shredding will help it break down quicker |
| Peanut hulls | Carbon | Shredding or chopping will help it break down quicker |
| Peat moss | Carbon | Also great to add to your garden soil |
| Pine needles and cones |
Carbon
|
Shredding or chopping will help it break down quicker |
| Tea leaves | Carbon | Best if shredded to help it break down quicker |
| Vegetable peels and scraps | Nitrogen | Kitchen scraps are a great source of nitrogen |
| Vetch | Carbon | From the pea family, yup add it too |
| Weeds |
Carbon
|
Don’t add if your concerned about spreading the seeds |
| Wheat straw | Carbon | Best if shredded to help it break down quicker |
Things you should NOT compost!
|
Materials
|
Carbon or Nitrogen
|
Details |
|---|---|---|
| Ashes (coal or charcoal) |
n/a
|
May contain materials that are toxic to plants. |
| Cat droppings/litter |
n/a
|
These may contain disease organisms and should always be avoided for composting. |
| Colored paper | ||
| Dog droppings |
n/a
|
Same as cats. |
| Lime |
n/a
|
High alkaline pH can kill composting action. |
| Meat, fat, grease, oils, bones |
n/a
|
Do not break down, can coat materials and “preserve” them, can attract pests. |
| Nonbiodegradable materials | ||
| Toxic materials |
Things that MAY be composted, but only with caution and skill
| Materials | C/N | Details |
|---|---|---|
| Bird droppings |
Nitrogen
|
Some bird droppings may contain disease or weed seeds |
| Diseased Plants |
Nitrogen
|
Make sure your pile gets to at least 135 degrees Fahrenheit for a few days to let it “therma kill” the disease |
| Milk, yogurt, cheese |
Neutral
|
May attract pests, so put it in the middle to deep into the pile |
| Weeds |
Nitrogen
|
For best results, dry them out until crunchy, then add them to your compost pile |
| Sod |
Nitrogen
|
Like diseased plants, make sure your pile gets hot enough to make sure the grass doesn’t keep growing in your pile. |
hi
thanks
i wonder about beans….are they like meat? i cook beans for two and inevitably have left over, can i compost? will they attract rats etc I live in the city…up til now i only am using raw fruit and veggie and grass leaves ….thanks (ex: pea soup, no oil, lental soup etc no oil)
thank you
_____________________________________________________
Hey there, Laura. Thanks so much for your question, it’s a good one! We’ve taken the time to answer it for you in the form of a video and blog post. Hope this helps. Have a great weekend, and good luck with your compost pile. Thanks for reading!
Terra Preta [black earth], found in the Amazon basin, is essentially compost with large quantities of charcoal. It creates very productive topsoil that is difficult to wear out. I’d like to attempt duplicating it; any recommendations?
———
I heard some NPR story or something about that, I think. I was not familiar with the concept at all until very recently, and I don’t know much about it.
I don’t know how to produce it, but I found this: http://en.wikipedia.org/wiki/Biochar
Oh, and I found the NPR story: http://www.npr.org/templates/story/story.php?storyId=92455289
Good luck!
Just starting wanting to do a compost bin. I made mine just out of chicken fencing wire. It is place under some trees so would not get real wet, nor real dry. Live in Iowa and have lots of corn shucks and cobs etc. Also, wanted to use it for my kitchen food waste, Did not realize until now that I could shred news print in with it to help.
Is there some kind of soil or stuff to mix in with it to get it started? Lois
————
There are plenty of compost starters or compost activators that you can use, but they are not required.
http://www.cleanairgardening.com/compoststarter.html
http://www.cleanairgardening.com/coac.html
http://www.cleanairgardening.com/compost-thrive.html
Corn cobs and shucks break down faster when you shred them before adding them to the pile.
Just want to check on using lake weeds in our compost pile! we live on Lake St. Clair and have lots of weeds growing up from the bottom of the lake. Can these be harvested and put into our compost pile? I know they are a good source of nitrogen. ALSO, we have a large community garden where we live…does the seaweed have to be composted before it is put in the beds? (Probably a dumb question, but thought I’d ask anyway!) Our veggie garden soil is low in nitrogen and phosphorus, which we can most likely amend next spring with organic fertilizers. Meanwhile, though, we do need to get those nutrients into the soil to help the poor plants which are struggling to survive! Ph yeah, and a coffee roaster friend of ours gave us a lot of coffee hulls, can they go directly into the soil? Any advice will be most appreciated!!!
—————–
Yes, you can compost those lake weeds. You should definitely compost them before adding them to your beds. Or at the very least, bury them at the beginning of the winter, so that they have all winter to decompose before you plant in the spring.
It seems that you can use coffee hulls as a soil amendment. It wouldn’t hurt to add some to your compost, too.
http://www.oisat.org/crops/economic_crops/coffee.html
“Return coffee pulps and hulls as organic fertilizer in coffee fields. These are rich in nutrients. A 60 kg bag of coffee pulps/hulls contains: 1 kg N; 0.60 kg P; .09 kg K and other trace elements. The pulp resulting from processing contains: 1 kg N; 0.84 kg P; 2.25 kg K and trace elements (Coffee Research Institute, 2001). “
I’m wondering about bread?
I’ve seen lists online that say both that it’s ok and that it’s not. Any recommendations?
————-
Bread is definitely ok to compost.
The only reason I could possibly think of someone saying don’t compost it is that it might attract animals that want to eat it. But if you’re adding it to a closed bin, or you bury under the top layer in your compost pile, that would solve that problem.
If you compost bread, what about the old bread on top of the fridge that has got moldy? Would this ruin the compost?
————-
It’s perfectly fine to add moldy bread to your compost pile. It won’t hurt anything.
Thank you for all your helpful advise
I’ve read cooked potatoes and citrus rinds should not be used in compost. Mostly because of the chemicals used to protect or feed them. Beside the potential rodent/vermin issues can I use cooked potatoes and citrus rinds in my compost?
Regards
————-
I would say yes to both things.
I’ve also read that in a few places about avoiding citrus rinds, but I compost them all the time and have never had trouble. The majority of composting books say that it’s fine to compost citrus.
The exception to that would be with vermicomposting. Worms don’t do well with a lot of citrus rinds. Regular composting is fine.
I’ve personally never read anything about not composting cooked or uncooked potatoes. Seeing how I sometimes eat the skin of a cooked potato, I can’t imagine that the leftover potato could be that bad for the compost if it doesn’t hurt me.
We’ve started composting recently and despite not adding any meat or dairy products, we have tons of maggots. It seems like they’re just eating everything and leaving very little but themselves behind. What to do?
Thanks!
————–
It’s normal for bugs and larvae to get into the compost. It’s not a big deal, and they aren’t hurting anything. They are helping the materials break down. Kitchen scraps often attract bugs more than yard waste, so I’m guessing you might be adding a lot of vegetable and fruit scraps and things like that.
Burying that stuff under more carbon rich materials like leaves will keep a lot of bugs from flying into the bin and finding the stuff, so that might help if you really don’t want to see any larvae.
Can I compost leaves from a black walnut tree? The leaves and nuts that fall from the one in our backyard seem to inhibit anything else from growing so I’m hesitant to add it to our compost pile.
———–
Please do not compost anything that comes from a black walnut tree, because it is toxic to plants, horses and even humans.
http://ohioline.osu.edu/hyg-fact/1000/1148.html
Great tips! Can diatomaceous earth be used to control insects in a compost pile? We currently use it in the hen house to diminish odor and flies. We also sprinkle a little around trees and plants but not sure how it might affect compost materials.
———-
My understanding is that diatomaceous earth doesn’t work very well when it is damp. And compost should be about the dampness of a wrung out sponge. So I’m not sure if it would be very effective.
I don’t think it would hurt anything to try it though.
I love to compost and have two active compost containers, which are doing very well, plus several large bins just for the end of the season garden cuttings. I was hoping that over the years it would turn into some nice usable compost, but it looks and feels more like dried straw material. My question is: will this ever amount to anything?
————
Sounds like you have the “too much of a single type of material” problem.
I would take some of that straw-like material and start adding it to your other active compost bins, a bit at a time. I think it will break down nicely if you mixed it in with other stuff.
Another tip is that if you have tough stalks of something that you want to compost, it helps to cut those stalks into smaller pieces. You can run over them with a lawnmower, or cut them with scissors, or run them through a chipper / shredder. Smaller pieces break down better and faster than large pieces.
Thank you for your response. Do you think its ok to use it to cover my plants for the winter. It all has been shredded with a chipper.
Thank you for your reply
I have been working with my red worms for 2 years and have had wonderful success with my garden using my worm’s castings for fertilizer. My husband saw a TV show about worms and wants to see if he can feed worms asphalt shingles, metal and wood. I am afraid that the compost would be toxic. I saw an article about super worms in Wales and it asks some of those same questions. Can you discuss this?
————–
Thanks for your question. I am only an intermediate vermicomposter at best. We have one worm bin going at work.
But I am skeptical that you could feed the worms asphalt shingles, metal and wood. Pressurized wood, for instance, is sometimes treated with arsenic. So although it doesn’t hurt to test, I would be careful with overloading your worm bin with a bunch of stuff that might be potentially toxic and might end up killing all your worms. In small amounts though, I guess you could try and see what happens.
I would strongly discourage anyone from using treated lumber and asphalt shingles in their compost. Not only are these items hazardous to worms, but many of their chemical constituents are not biodegradeable and will stick in the soil for many years. These toxins, when absorbed by plants (and later ingested by you), are usually carcinogenic. A good rule of thumb is to keep your compost as clean of chemicals as possible. Stick with food scraps, yard clippings, and other organic matter.
what about onions?????
———
Yes, onions are fine. Onions are covered under the category of “fruit and vegetable scraps.”
ah!! thankyou so much!!! have found your site to be extremely helpful and interesting!!!! thanks heaps!!
Can you compose in the winter? If so how do you turn it when it freezes? Thank you Cheryl
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We have a page about composting in winter here!
https://www.compostinstructions.com/composting-year-round
What about Eucalyptus leaves? We have a tree in the front yard, the only one in the yard that shed leaves, and I think it is a Eucalyptus globulus tree(at least thats the best I can tell from the pictures online). Are the leaves safe to put in the compost? They are kind of thick(not succulants though), and have a potent smell when rubbed or broken.
———–
Great question! I didn’t know the answer to this one, and had to look it up.
It turns out that University of California Davis has studied this issue and determined that Eucalyptus leaves are safe to compost, but very slow to break down because of their oily leaves.
So I wouldn’t try to compost too many of them at once, because it might be a challenge to get them to break down well. But in limited amounts, you should be fine. And they are safe.
My husband and I are renting our first home and I’m excited to start composting as about 70% of our weekly garbage is compostable. It appears as if the family who lived in the house before us set up a wire composting bin directly behind the children’s swingset in the back yard. I was wondering if that was in any way dangerous in terms of toxic fumes, children eating the dirt, etc.
Thanks for your question.
I answered it here with a blog post:
https://www.compostinstructions.com/composting-toxic/
I saw peanut hulls on your chart but it doesnt specify weather its carbon or nitrogen? please let me know.
Thanks
Good question!
I’m not entirely sure of the answer, to be honest. It won’t be nitrogen rich though.
I’m guessing either carbon rich, or neutral. I would lean toward calling it carbon rich.
What about sugar? We have a box of confectioners powder sugar that the ants got to and want to know if we can compost it. The box says “w/out preservatives or trans fat”, ingrediants are “sugar, cornstarch”, and the brand is “C&H”.
Yes, it’s fine to compost, although it might attract ants.
Best to bury it in the center of the pile or bin.
I am currently composting using a rolling drum in my backyard. It was 50% full of kitchen waste. I dethatched my lawn and put all of the dry dead grass and moss in the bin. I just read that it isn’t ok to compost yard waste treated with weed-b-gone. I used Scotts fertilizer with moss control and now I’m worried that the whole bin of compost is toast. Any insight?
@Apryl,
I guess it depends on how long ago you used the moss control product on your grass.
The issue in question is that if you are composting something that has been treated with an herbicide and it hasn’t broken down completely, your finished compost might still have herbicide in it, which could harm vegetables, flowers or shrubs.
There is a solution though! Only use this batch of compost on your grass, where you already used that treatment anyway, and you’ll be fine.
I am tired of wrapping organic matter from the kitchen in plastic and sending it to the landfill. Can I just sprinkle my peels and celery tops etc around my acreage. Will it attract animals? I really don’t want another thing to maintain around here so a compost bin doesn’t appeal to me. Thanks
@michele,
Although just throwing it on the ground will indeed work, it can attract rodents and pests.
A better option would be to simply bury your materials if you don’t want to mess with a bin or a compost pile.
I have a few questions. I am a very beginner to composting, and I saw this online: http://dinnergarden.blogspot.com/2009/05/dinner-garden-learns-to-compost.html
I wondered if something like this bin thing would work? I have a very small garden, so we decided to try this bin thing.
We set up this bin thing like they said on their website, but I see from your information that I should probably drill some holes in the bottom, too, for drainage. Also, we put in a lot of dandelions and some thistles, with some leaves and some soil to get it going. What else should I use? How often should I turn something like this? We have a pet house rabbit (herbivore of course), and I see I can use his litter as well. Oh, and I see you have weeds in the “ok to compost” and in the “May be composted but with skill” section. Since we are definitely not skilled at this, is using the dandelions and thistles a problem?
Why does the compost start to mold? How do we get rid of it
I’ve been wanting to compost, and I am just beginning are u not suppose to compost cooked food….if they’re scraps.I know u can’t compost meat, but what about shells (specific) to sunflower seeds, or any other nut for that matter? Also bread…..Is it pretty uch anything that has not been cooked?Thanx
I’ve read that eggshells are great for composting, but what about the whole egg?
@Patti
Eggs (as opposed to just eggshells) can become putrid and stink and/or attract rodents if you add them to your compost pile or bin. So I do not recommend adding whole eggs.
Please read this article on the use of eucalyptus in composting: http://slosson.ucdavis.edu/documents/1993-19942140.pdf
More on the benefits of Eucalyptus in composting for plants and vegetables… A California research project on Eucalyptus leaves in compost:
http://ucanr.org/repository/CAO/landingpage.cfm?article=ca.v047n03p22&fulltext=yes
The finding that both sludge products similarly affect crop growth indicates Eucalyptus trimmings (present in the compost, but not in the heat-dried sludge) do not suppress crop growth at the rates being evaluated in this study. This is an important point because it was initially feared that allelopathic compounds in the Eucalyptus would inhibit crop growth. The authors hypothesize that the composting process degrades the allelopathic compounds into harmless products.
In summary, the field experiment showed that incorporating sewage sludge compost 4 inches deep as a soil amendment in spring plantings significantly increased yields of onion, snapdragon, turf and spinach. Greenhouse experiments produced similar results and demonstrated that the presence of Eucalyptus trimmings in compost does not depress yields.
I live in Alaska and just started my compost pile today. Is there anything I need to do to protect my bin and composting material in the winter? I live in an area that can get to -35 F.
@Renee
Anything that you do, the pile will still freeze solid during the winter. But it’s no big deal. The composting process will stop when it’s freezing, but it will start back up again naturally when the snow melts away next year.
I’d be worried more about the bin itself than the materials, but I’m not really an expert on super cold weather like that, so I don’t think I’d have anything constructive to recommend.
Wait, can you compost nitrogen items and carbon items together?
@HannahDaizy
Yes, absolutely. You are supposed to have a mix of carbon rich and nitrogen rich materials for optimal composting. Too much of one or the other will cause problems and slow things down.
Hi Lars!
I LOVE this SITE!!!! So helpful!!! I’m new at composting… I took a Plastic plant container, cut out the bottom, turned it upside down on the turned over Soil, and put my kitchen scraps in it to start. What should I do next? Should I add anything to it to get started in breaking down, or should I just wait? Thank you so much!
Oh, I put a wire cage around it and on top of it to keep out Cats in the neighborhood… So, my Container is technically “open” and moist…there is a Water Source nearby…
O.k…I bought a compost bin yesterday and put it together! It came with come Composting “Seed” I think is supposed to help it along… I put some Grass shavings on top of my Kitchen Scraps and poured H2O on it… Do I need to do anything else to it? I did give it a toss. I put it in a great area that gets lots of sunlight. Thanks!
When the composting process is finished and you have your product compost, do you have to use it right away or can you store it until you are ready to use it for your garden?
Soil doesn’t loose its nutrients unless there is something to use them. Feel free to store the compost away, just check on it every here and there to make sure that there are not any plants growing in it.
Can you compost left overs from the kitchen such as spaghetti or casserole dishes?
I like to go to Starbucks and get the spent coffee grounds to add to my compost. It seems to really heat up after I add a fresh batch…
A month ago I composted some of my expired dried herbs, including about 6 oz. of black walnut hull powder (BWHP). I didn’t realize that black walnut hulls might be poisonous to some plants, birds and worms. My compost pile doesn’t get superheated and is about 4×4 in diameter with about 12 inches of material in it. Would it be alright to use this compost in my garden with the BWHP in it, or should I start from scratch and dispose of the pile? Or do think that 6 oz. won’t harm anything?
can i compost drum rolling tobacco butts in my tumbler compost bin?
thanks!
I did not see bread in the list of things that can be composted. Can starchy foods like potatoes and rice can be composted ? What is the problem when we see mold appears in parts of the compost.
Ok- so I am so so new to this composting thing….I have a tumbler composter and I threw in a bunch of saved up veggie/ fruit/food scraps, then some leaves, then some tree clippings, topsoil and hay. Now, if I keep adding more veggie/fruit/food scraps, how will the compost ever be “done” and ready to add to garden? Do I just add enough to make one “batch”, then empty that and then start over?? Thanks so much- great website…best I have found!!
Do you recommend composting rice and pasta, since bread is ok?
Can you compost used fish water ? like what you get when you clean it out ?
@Dereck
Yes, you can pour the used aquarium onto your compost pile and it’s okay. If it’s safe enough for fish to swim in, it’s safe enough for your compost pile!
what about activated carbon from water filters? It is carbon but it’s made from charcoal which the above says that charcoal may be toxic but the carbon is purified from it. I’m unsure though this is what I’m talking about. http://en.wikipedia.org/wiki/Activated_carbon
@dereck
I’d probably skip the activated carbon from the water filters, just to be safe. It probably wouldn’t hurt. Because after all, the fish were living in water that was circulating through it. But I’m not totally sure about that, so I probably would just skip it.
I am now ready to compost. I bought a popular brand 18 bushel compost tumbler. I live on a one acre sight with lots of prairie type grasses. I de-thatched my one acre this year ane have a pile of what is mostly carbon. I understand mostly what and what not to put in the rolling bin and the moisture of what I do put in the compost bin. I understand that I will need to add the nitrogen and want to use manure. The manure I am planning to use is from my home gardening store but it says it is steralized and I dont know how much to put in each load. Thank you, Samuel
@Samuel Roberts, Start with a 4 to 1 ratio. Four parts carbon to one part nitrogen. Keep it as moist as a well rung out sponge. I assume it has vents so over watering is not a problem, excess water will drain out. You typically know if you have too much nitrogen if it begins to clump up in balls. You will know if you have too little nitrogen if nothing is happening, i.e. it is not heating up.
I have two guinea pigs at home and I was wondering if their bedding can be added as well. I understand the herbivore droppings being used but what about urine soaked pine and cedar shavings??
Thanks
Bill
@Bill
Yes, but.
It’s okay to add those, in my opinion. But cedar / pine shavings take a really long time to break down. So if you’re going through a lot of that bedding, you could easily overload your compost pile and end up with too much cedar that isn’t breaking down.
@Bill Parson, Yes, you can use them.
hi,
can you add lemons to compost, or is to acid?
thanks
@lenne, Typically I avoid them, however if you only add a few and its a very small part of the overall compost mix you should be fine. I would not make a habit of adding more than a few per batch of compost. You may want to chop them up as well and maybe even set them out to dry out before adding them to your compost pile or compost bin.
Hi,
I heard it is good to add ‘compost’ to compost,
but what about ‘used soil’ that for example I’ve had for my indoor plants? (since it usually contains peat, and the air is sort of out, can this be damaging?)
Kind regards
@Sarah, Yes, adding finished compost to a new pile is helpful. It basically jump starts your new pile by giving it the needed microorganisms that break down the compost in the first place. Adding used soil even from a potted plant should not cause a problem, especially in a limited amount of a few plants
hi i hope im on the right track> the wife and i built are first compost box yesterday. it is 6feet long and 3feet wide and 3feet high we divided it it to two boxs all walls have a one inche space between boards. we started out with twing and leafs on the bottom some straw horse manure grass and some chicken manure some cardboard we are about 1/4 full so far shouid i just keep repeating this step thankyou for your knowledge and God blessing to you Rod and Gloria
one other thing I would like to ask yesterday when putting is some older garden compost that we had in a pile just outside on the ground had some worms in it. we put a good couple of pichforks in the new compost box of this stuff and a wheel barrow full of one year old horse manuare it also had worms in it. is this ok Thankyou Rod and Gloria God Blessing
one thing i would like to ask, it is correct that the compost pile must be covered with a plastic to produced heat? i just wondered, could it affect the passage of oxygen?how about the activities of the bacteria
could it vary the decomposition process???
thank you for helping me.
@chariz, Typically plastic is used to keep the bin from drying out. If you do cover it, just make sure you turn it once or twice a week and it will be fine. I guess another reason someone might cover it during the winter is to help keep it warm.