Leaf Mold

Leaf mold, leaf mould, duff, humus

I've been giving leaf mold much attention lately. Online information is scarce. It seems to be a terribly overlooked, under appreciated, and especially useful material. I've been meaning to post some notes about leaf mold but it seems like the days are not as long as they used to be, even with setting the clocks.

Leaf mold, quite simply, is rotten leaves. To produce leaf mold, pile up a bunch of leaves and leave them alone. Just leaves, nothing else. It may take a year, maybe 2 if its cold or dry, but eventually they will decay. What you end up with is stable humus. The properties and benefits of using leaf mold are plentiful. I view leaf mold as being as important as compost and mulch. Being free, the price is right, and fits in my budget. It can take time to gather a pile of leaves, but there are plenty of people out there gathering up leaves for me, bagging them up and placing them beside the road in a neat stack-this really saves me a lot of work!

Leaf mold is not the same as compost. Compost is produced by bacterial decomposition. Leaf mold is produced by fungal decomposition. Compost is hot, aerobic, and quick. Leaf mold is cool, slow, and can be produced with little oxygen. This means you don't have to turn it. Where compost needs a variety of ingredients to attain the right carbon to nitrogen ration to feed the bacteria, leaf mold needs only the one ingredient-leaves. Leaves have a CN ratio ranging from 80:1 to 200:1. There is some nitrogen available, but not enough to allow the bacteria population to explode.

Down here in Florida, the state does not recognize the distinction between bacterial and fungal decay. The state's definition of compost includes any and all decomposed organic matter, and it must be sterilized in order to be sold. This is part of the reason why leaf mold is not available commercially. Another factor is the time it takes to produce the stuff. It's a darn shame. The fungus in the leaf mold, when added to the soil, serves as a nutrient superhighway. Sterilizing leaf mold would destroy the fungus. If the state had any idea what is going on, they would make the distinction, and create an entire industry overnight. I've looked high and low for sources of commercial leaf mold, found one in Texas. Where compost prices range from $20 to $35 per cubic yard, the dealer in Texas listed $100 per cuyd. That's 10¢/pound! For leaves! With the drought in Texas, the horse and cow people are buying up hay, driving up prices all over the south. An 800 pound bale used to be $20, now it runs me $40-that's 5¢/pound. The price of hay is through the roof, yet leaf mold is still twice the price.

Soil Conditioner
Leaf mold serves as a soil conditioner rather than a natural fertilizer. It primarily changes the structure of the soil rather than serving nutrient needs. Its the fungus. All the little hairs of the fungus grabbing onto soil particles help to bind loose soil, while at the same time the hyphae helps to break up compact soil. The natural growth habit of the fungus will move from the leaf mold to the surrounding soil in all dimensions. Start with a small area of leaf mold, end up with a greater volume of better soil. Leaf mold will continue to break down until the only thing left is stable humus which will remain in the soil for decades to centuries, taking a fire to destroy it. Until then, the leaf mold is rich in organic components: humic acids, carbohydrates, lipids, and stuff I never heard of. It is complex and impossible to manufacture. As the foundation of the soil ecosystem, there is nothing better.

Water Retention
I've read claims that leaf mold will hold several times it's weight in water. So I checked into it some...
I've been raking up the massive volumes of leaves around here. Some I ran over with a mower to chew into small bits. I sifted some of this material through 1/4" mesh, filled up a trash barrel so I'd have something to experiment with. It's real fine stuff let me tell you. I weighed out 4 ounces of this dry material, enough to fill a 16 ounce drinking cup. This went into a bucket. Weighed the bucket, then added water. The next day I drained off the excess water, weighed it again. The 4 ounces of leaves held 18 ounces of water. It's not a big enough data sampling to be greatly accurate, but it held 4 1/2 times its weight in water. Impressive.

Minerals
NPK values of leaf mold are nothing to write home about. I've seen it listed around 2.2 - .8 - 1.6, or so, depending on the species. What leaf mold brings to the table are minerals. The roots of trees accumulate nutrients from deep in the ground, sending plenty to the leaves. While the nutrients are drawn back into the tree before the leaves are shed, most of the minerals remain as they are part of the leaf structure.

www.composterconnection.com wrote:Pound for pound, the leaves of most tress contain twice the mineral content of manure...And they provide the perfect nutrition for beneficial microbes. In short, they make soil come alive.

For this sandbar of a state I live in, there's not much in the soil. I'll take all the help I can get. Leaves are abundant. With the drought of the last couple of years, the leaves out back are 6 inches deep in some places. The woods around here are a mineral warehouse.

Excellent post!

I love leaf mold, we have a friend who's little front garden completely fills up with leafs every autumn. For the last couple of years I have collected it and rotted it down in a big hoop of chicken wire. After a year or so it has turned into beautiful rich black humus, it really improves my heavy clay soil and is always filled with mycelium, worms and other bugs and beasties.

Nice thread. Leaf mold is a great soil amendment. For fastest decomposition, leaves need to be in direct contact with the soil.
Urine will greatly speed up the decay...a little nitrogen does wonders for the process.

Here are a couple links regarding leaf mold:

http://www.paghat.com/leafmold.html

http://www.bbc.co.uk/gardening/basics/techniques/soil_makeleafmould1.shtml

Ah, thanks!! A friendly neighbor who has been regularly giving me bags of soiled lucerne for free (lots of vegetarian pets in her home) just popped around with ten huge bags of already decomposed leaf mulch. Apparently it's been sitting around in her backyard causing her grief as she has no time for gardening. I feel like all my Christmases have come at once

2 easy ways that I have incorporated leaf matter . Mulch around fruit trees , it helps to get that woody matter into the soil and fungal biota started. I also turn some into the garden soil where I will plant potatos. Then the following year they have broken down into soil .

Thanks, great info. I copied this post and am going to print it out for my mother. Hopefully it'll make her feel better about the 30ish bags of leaves stacked oddly around the garden, that are being used in place of/in conjunction to regular raw compost.

John Polk wrote:Nice thread. Leaf mold is a great soil amendment. For fastest decomposition, leaves need to be in direct contact with the soil.
Urine will greatly speed up the decay...a little nitrogen does wonders for the process.

True...however...nitrogen promotes bacterial decomposition. Without the nitrogen, fungal decomposition will be the primary means of decay. The difference is subtle and I'm just starting to get my noggin around it. If I am understanding things correctly, the high lignin content of leaves combined with fungal decomposition produces more humus than the compost process. Lignin is a precursor to humus. It's the humus that serves the soil, increasing the CEC, cation exchange capacity, which plays a significant role in holding available nutrients in the soil. This humification process also sequesters more carbon in the soil than the compost process, which releases it as CO2.

edited for spelling

Should I sweep up all my leaves and pile them up between the shed and the back fence where it's shady and cold and I have no intention of gardening? There's only a metre width there and obviously it's in permanent shade.

It would be a way of putting that space to good use.
Mind you, decomposition of wood in the shed wall and fence boards will also be promoted if kept moist and piled high with leaves. Protect your infrastructure.

I had a big mound of leaf mold in my front yard, and noticed insane germination and astonishing growth of weeds. Lambsquarters grew about seven feet tall! Later on I learned that the fungal decay involved produces gibberellins, and I suspect that's what produced the phenomenon. Since then I've incorporated it into my seedling mixes to good effect.

Leaf mold is said to be an excellent substitute for peat moss in potting mix. I used to buy peat moss, about 10 bucks for a compacted bale 1'x1'x2' or so, uncompacted was 3 cubic feet. Finely shredded leaves is also a pretty good substitute, and the price is right.

Wikipedia's gibberish on Gibberellin.

It is interesting that the Wikipedia article has a picture of a perky little cannabis sprout under the influence of gibberellin. Maybe leaf mold will be the new bat guano and potheads will leave those little bats alone. Leaf matter under fruit trees is the best way to eradicate sod and free ranging chickens will tear it to shreds and get quite a few bug meals from it too. And fertilize the trees.

I have always raked the leaves off of the lawn paths into the borders around my property and even off the paths in the woods and left them under the trees, and we have had some pretty severe droughts here in Michigan lately..and the areas that have the leaves piled up and decomposing are seldom dry..even with 2 months with no rain last year..they stayed moist and cool.

My other gardens that had no leaves dried out terribly even the mulch I put on got gobbled up by worms so fast I could hardly keep any on top of the soil ..but in the beds with the leaves piled it was rich, cool, moist.

I am cautious about bringing anything raked up on strangers properties though, as you never know what kinds of chemicals or pet diseases might be in them..i used to bring home leaves from town, but then our maple trees got infected with something that looked like cigarette burns on them and I noticed that it was in the leaves I brought from town..not good..so I don't do that anymore.

Thanks, Ken, for posting. As you pointed out, leaf mold is dominated by fungi, while compost is (usually) dominated by bacteria. Compost made specifically from cow manure has more fungi than most other compost. One can make fungi-dominated compost tea by using leaf mold as an ingredient, which means it is really leaf mold tea. You can also do this by using molded oatmeal as an ingredient. To really boost the bacteria, use fish puree and epsom salt to enhance the breakdown of the fish, releasing lots of nitrogen. You can even make protozoa dominated tea by using fresh grass clippings as an ingredient, but let me get back to my main point which is about how we can use these microherds to manipulate soil pH.

Fungal-dominant microherds in molds, mulch, or teas are more acidic than bacterial dominant microherds. To simplify, I'll call the former fungal innoculant, and the latter bacterial innoculant. If the soil is too alkaline, you can use fungal innoculant to lower the pH. If it is too acidic, use bacterial innoculant.

I use both, depending on what I am growing. Our soil is naturally too acidic for most of our fruit and nut trees and most of the other plants as well. That's because most of those plants are mid-succession species that like the soil pH in the middle range. So, I make bacterial innoculant most of the time. It helps apples, pears, peaches, pecans, etc to adapt to our acidic soil. For acid lovers like blueberry, blackberry, sweet potato, watermelon, basil, rosemary, potato, I use fungal innoculant like leaf mold and molded oatmeal tea.

I think every location has it's own specific challenges and the key is understanding what to do with the soil and climate that you have to work with. Our soil is so acidic, that I felt I had to incorporate some lime for many of our trees. Lime, because the calcium and magnesium are not readily soluble, has a more lasting effect even than bacterial innoculants. We get so much rain during the wet season, a lot of the soil nutrients get washed down through the sand deep beyond the reach of many plants' root systems. I suspect that it will be critical for the deep tap rooted deciduous trees in our food forest like pecan, chestnut, persimmon, paw paw, jujube, and mulberry to get large with very deep roots to capture those nutrients and bring them back to the surface of the soil when they drop their leaves. I'll probably have to import a lot of mulch over the next few years until that happens. I'm glad a lot of people don't value leaves and wood chips and gather them up for me to take for free.

Thanks again for starting this topic.

Just after submitting the previous post, I happened to notice my blueberries looking chlorotic. We've had 15-20 inches of rain in the last 3 weeks. I suspect the deluge has washed away nitrogen or raised the soil pH or both. So, I'm now making two batches of leaf mold tea to be applied in 2 days to try to restore some order. I'm also going to add 3 more inches of shredded oak mulch. Several months ago, one of our neighbors made a pile 6 feet high on the side of the road and put a sign in it reading "free mulch". It already has some good fungal micelia. Sometimes things just work out.

turns out you need leaf mold to break down the flavinoids in the leaves.
They are antibacterial, so the mold works first, then the bacteria can come in and finish the job