"leaves should be composted separately because lignin is broken down by fungus and not bacteria"

Is there any accuracy to this statement?

If that were the case, wouldn't that mean that sawdust wouldn't break down in a compost pile (im thinking Jenkins) until the pile cooled down enough for fungus to infiltrate?

What does that mean in practical application for composting? Should leaves and wood chips be kept out of the compost pile?

I heard that leaf piles will heat up. I thought only bacteria give off heat when they are at work. What gives?

"Lignin is broken down by fungus and not bacteria" True. Lignin is a disordered polymer, hard for bacteria to digest; they do much better converting cellulose back into glucose and eating that.

Sawdust is mostly cellulose, so in a compost pile, the bacteria are humming away. That's why compost piles get hot.

Leaves also contain cellulose, enough so that piles of them can get hot from active bacteria.

As for the first part of the premise, "leaves should be composted separately", nah, I can't really be bothered to do that, I'm making compost, not haute cuisine. Just throw it in a pile and wait for it to break down.

I dunno....I've been making great compost with leaves and grass clippings for over 30 years! Heats up fast and breaks down in 2-3 weeks.

dan long wrote:Is there any accuracy to this statement?

I would say no because in a forest they are composted together naturally.

IDK Pardner.... I made my compost using 3 year old wood chips and horse manure last year. Not sure that was a good idea... It's really full of sticks. Kinda thought we might have to use it as "Mulchpost." The chip pile had been heating for months, and I used the California Hot Method, as usual. Pile seemed to heat up OK, but it sure has the sticks, still, and I wasn't prepared for that!. Best, TM

Tim Malacarne wrote:... I used the California Hot Method, as usual. Pile seemed to heat up OK, but it sure has the sticks, still, and I wasn't prepared for that!. Best, TM

So maybe sticks are not so good with the that quick method because of their size? Is that the 18 day Berkley method?

dan long wrote:Is there any accuracy to this statement?

Yup.
Leaves are primarily composed of lignin. Bacteria can not produce the enzyme Lignase, which is required to break down lignin. ONLY fungi can produce lignase.
Bacteria will break down cellulose, heating the heap in the process. A hot compost pile can kill off the fungi. When the heap cools, the fungi will move back in to finish the job. Without the leaves, the compost heap will be finished considerably sooner. Segregate the leaves into their own heap for decomposition. While there will be some bacterial decay, the leaf heap will not reach the extreme temperatures, giving the fungi the opportunity to establish a population and get to work sooner.

Leaf mold (Thread, Article) differs from compost. Where compost is rich in nutrients, leaf mold is rich in minerals.

Of course, you can just let the compost "finish" breaking down lignin in or on the soil. Fungal breakdown doesn't need a large hot heap.

I have to disagree. I've been making GREAT HOT compost with grass clippings and leaves (along with the kitchen waste) in 2-3 weeks for well over 30 years!
Apparently the thermophile bacteria on my land didn't read the same book(s) you did. I believe that a Google on composting with leaves would confirm this.

Ken Peavey wrote:

dan long wrote:Is there any accuracy to this statement?

Yup.
Leaves are primarily composed of lignin. Bacteria can not produce the enzyme Lignase, which is required to break down lignin. ONLY fungi can produce lignase.
Bacteria will break down cellulose, heating the heap in the process. A hot compost pile can kill off the fungi. When the heap cools, the fungi will move back in to finish the job. Without the leaves, the compost heap will be finished considerably sooner. Segregate the leaves into their own heap for decomposition. While there will be some bacterial decay, the leaf heap will not reach the extreme temperatures, giving the fungi the opportunity to establish a population and get to work sooner.

Leaf mold (Thread, Article) differs from compost. Where compost is rich in nutrients, leaf mold is rich in minerals.

Case in point...Here is the heap I built just 4 days ago. This heap was made with leaves, grass clippings (cut winter rye) and kitchen waste. The temp went to 80F on day 2, 120F day 3 and 4. In this photo the heap is broken down. I use my Mantis tiller with straight tines (designed to be used for lawn aeration). This chops and mixes the contents of the heap.
As you can clearly see, decomp is well under way in only 4 days. For moisture I use a hose end sprayer to lace the water with Grandmas unsulfered molasses.
(I restacked and will break down every 2-3 days until done.)

120*F is not considered 'hot composting'.
To do hot composting, you need to reach temps in the 160-170* range.

When you get to the 160-170 range, the fungi will slow down until your temps get back to a cold composting temp (+/-120*) after the bacteria have done their job (ran out of food), and begin dieing off.

With a lot of leaves, you are better off doing them apart from the rest unless you have tons of greens (N).
If you have lots of greens, add enough leaves to get your 30:1 C:N ratio.
Too much N, your pile will just rot.
Not enough N, your pile stays cold (+/-120*).

I believe separate composting results in the precious material lauded by old time English gardening books, leaf mold, an "excellent humid soil conditioner" with characteristics of woodland ecology. If you want leaf mold, you pile your leaves up separately for a couple years. Do you want it? It depends...

Is there any truth to that statement?

Well, what exactly are you trying to do?

Are you trying to kill off weed seeds?
Are you trying to heat your water for showers?
Are you trying to make compost freakishly fast?

Or, are you just trying to make a good fertilizer? Because if it's any of the first three, definitely, you want to compost leaves separately. But if you are just trying to make good fertilizer and don't mind waiting a little while longer, it's probably not worth the bother. However, you do want to make sure you get the ratio of C:N correct, and leaves generally don't come at the same time as everything else, so I generally do have a separate bin to store leaves to add to the general compost pile a little at a time.

Actually the optimal temperature for 'hot composting' is 130-140 as temps too low and too high are less productive. I'm unsure of the accuracy of my compost thermometer (I'll need to test in a glass of ice water), but look at the picture and tell me that's not a respectable amount of decomp in only 4 days! Also I'll expect a temp rise after this first chop/mix/turning as the ingredients get more familiar then they were in the layering.
Still to the contention that leaves should be composted alone and separately into 2 year leaf mold, I say dry leaves are mineral rich and make an excellent brown in a compost heap.
Alternatively, there is a school of thought that suggests that cold composting (that is just pile organic waste and let it rot for a year or two) is better than 'hot composting'.
Better still is to just pile it all in the garden as mulch or in the fall (sheet composting - in areas where there is a winter) and let the garden soil food web process the material. This actually makes for less work and probably yields better overall results....promoting no till.

regards,
Mike

John Polk wrote:120*F is not considered 'hot composting'.
To do hot composting, you need to reach temps in the 160-170* range.

When you get to the 160-170 range, the fungi will slow down until your temps get back to a cold composting temp (+/-120*) after the bacteria have done their job (ran out of food), and begin dieing off.

With a lot of leaves, you are better off doing them apart from the rest unless you have tons of greens (N).
If you have lots of greens, add enough leaves to get your 30:1 C:N ratio.
Too much N, your pile will just rot.
Not enough N, your pile stays cold (+/-120*).

dan long wrote:Is there any accuracy to this statement?

If that were the case, wouldn't that mean that sawdust wouldn't break down in a compost pile (im thinking Jenkins) until the pile cooled down enough for fungus to infiltrate?

What does that mean in practical application for composting? Should leaves and wood chips be kept out of the compost pile?

I heard that leaf piles will heat up. I thought only bacteria give off heat when they are at work. What gives?

The accuracy to the statement is that lignin is broken down by fungus not by bacteria. That is factually correct.

The rest is debatable and depends on what you are trying to accomplish and how you wish to go about doing it. Leaves contain both lignin and cellulose, so there is material that bacteria can break down and material that they cannot. Bacterial composting will break down the cellulose, but not the lignin.

Pile the leaves separately and let the fungal processes do all the work and you wind up with leaf mould, which is different than the compost product of hot composting, and definitely useful and beneficial in its own right.

Put the leaves in a hot compost pile at appropriate ratios and you will end up with compost (that still has lignin in it waiting to break down, but the soil web fungi will be happy to do that) and that is useful and beneficial stuff.

Compost according to what you need to get out of it.

I dont follow any kind of scientific regime. I put grass clippings, leaves and any and all organic material in a pile and turn it about once a week. I just add to the same pile as I go. I mulch heavinly every thing with leaves becasue I have an endless supply of free oak and maple ;eaves that blow onto my property whether I want them or not. In the fall I spread my pile of partialy composted material on my garden with more leaves and let the worms finish it for me.
I have been doig it since I bough my half acre three years ago and it seems to do what I want it to in that my soil is getting better all the while. I do plan on chickens to process my compost pile next year and I will be getting some rock dust to spread around for micronutients but all in all it is working.

Just a followup: I checked the calibration of my compost thermometer and it is spot on. After the first turn, the temp held at 130F (up from 120F) for two days. I broke it down and restacked yesterday (really cooking nicely).

Another two days - the temperature was just under 140F, here's the pile broken down and restacked: