Building soil: what to do with leaf mulch

Last fall in an effort to build up soil in my so-called "raised" beds I put in a lasagna garden of sorts. Topped the bed (4 x 25 ft) with paper feed bags, then compost that was sorta kinda on it's way to becoming soil, then dumped a bunch of soil I scraped off the forest paths in my woods, and finally topped it all with lots of fresh, dried big leaf maple leaves.

I noticed the other day that the leaves look hardly any different than when I first put them on the bed last fall. But when I walked over and looked underneath the leaves I had gorgeous new soil!

I'm not sure why the leaves didn't rot, but it occurred to me maybe I could leave them there when I go to plant in a couple of months, thinking maybe they would help keep the soil moist, and keep heat inside during the colder months of early spring. Is that a good idea?

I'm not sure you can expect the leaves to decompose in such a short period. I know that all the dried leaves I piled in my various beds haven't broken down entirely. Even the volunteer lettuce that got killed by super-low temps this winter is still kinda goopy-stringy looking.

If you don't mind a bit of light tilling, maybe turn them into the soil a bit? Might help them break down faster.

But I would think they might be doing a better service as much at the moment. Figure they'll break down in their own due time.

I would take the leaves off in the early spring in order to allow the soil to get warmed up. If not, the leaf mulch will insulate the cold soil against the warming air temperatures and delay your season. After that, I think leaves are great to use as mulch during the summer and fall.

I have alot of large maples in my yard and get a huge amount of leaves each and every year. I put them in a pile in the garden in the fall. The stuff on top will decompose a bit, and the leaves on the bottom will rot into mulch, but the stuff in the middle will look the same in the spring. I use alot of them when I double dig sections of the garden, layering them in with the sub soil, the rest I spead out over the garden. You can till them in and they will rot much quicker, or you can let them on top as mulch. They will eventually rot up. They will keep the soil cooler, not warmer if left on top of the ground. You can just rake them back, plant your seeds and wait untill they sprout. Then rake the leaves back around the plants to hold moisture. If you use them every year you may want to add some lime occationally to sweeten the soil a bit, the leaves are a bit acidic.

Leaves you can use as mulch... or compost them.

Either way, they end up in your soil. Either way is good. Leaves are the leftover nutrients from your trees, minus the chlorophyll.

Leaves fertilize the trees they fall from... so if you rake them up and move them somewhere else, the trees will lack. Prioritize.

I've heard that 60% of the nutrients trees uptake in a year are discarded in the form of their leaves.

I pretty much have to rake mine up and manually redistribute... the flat land means that winds will carry them off somewhere else well before they have a chance to decompose if I don't. So into the beds they go!

Now that I live out here in the woods I've given considerable attention to leaves. The things are abundant-I can't rake them all up even with machinery to help, the things are easy to handle, and the price is right.

Deciduous trees draw up nutrients and minerals from the ground, grow leaves to make use of the sun's energy, then withdraw the nutrients from the leaves at the end of the season. What falls to the ground has limited nutritional value, but the mineral content is what makes them particularly useful. They also contain high levels of lignin and cellulose.

How the leave break down matters. With all that lignin and cellulose, the CN ratio is high. Depending on the species this can range from 60:1 to as high as 300:1. Adding green material to the leaves will give you a fine compost. Adding leaves to your soil before they have decomposed will promote the soil bacteria to use up available nitrogen to break down the leaves. This will slow down growth in the treated area until the nitrogen levels return to normal. The magic is what happens without the added greens. Fungi can decompose the leaves without the N, and can do it with limited oxygen. This is leaf mold (mould), the properties of which are different than compost.

To Make Leaf Mold
1 Pile up a whole bunch of leaves.
2 Get them wet if you like.
3 Come back in 2-3 years, remove the top few inches to reveal a rich, black, stable, mineral rich humus.
This process takes time and there is no speeding it up. Adding greens does not speed up the process, it makes a different process known as compost. You don't have to turn it. You can keep it moist, but it's a multi year process. The heap will warm up quickly at first as the bacteria take the upper hand. Once the nitrogen is used up, the bacteria die off and the fungi take over. If you want some of this stuff, you have to make it and wait for it. It is not a commercially available product. It takes too long to produce to be commercially viable. Furthermore, some states require that soil amendments be sterilized. Part of what makes the stuff awesome is the fungal population.

Leaf mold can be applied to your soil any way you like: as a surface mulch around plants or spade/till it in. Because of the manner in which the trees withdraw nutrients before discarding the leaves, leaf mold does not offer nutrients for your plants. However, the structure of the lignin, cellulose, and humic acids provides a highly active bonding strata. This means the stuff will hold on to nutrients and minerals, but not so strongly as to lock them up. The process keeps the nutrients and minerals available in a manner the soil microbes can access readily. Since it has already decomposed, it will not rob your soil of available nitrogen. Leaf mold adds the minerals your plants need: manganese, copper, iron, boron, magnesium, zinc, and god knows what else.

The material is lightweight for its volume. Adding it to the soil improves tilth. As a soil conditioner, leaf mold can't be beat. If you've walked around the floor of a dense forest, you've experienced how spongy the ground is.

The material holds a great deal of water. My measurements show about 4 times it's own weight in water holding capacity. 2 pounds of leaf mold will hold a gallon of water. 2 pounds of leaf mold per square foot will hold the equivalent of 1.6" of rain. There is not really a limit to how much leaf mold you add to your soil. I've seen estimates of 10% leaf mold content per cubic foot still improving the soil. A cubic foot of soil will weigh somewhere around 100 pounds. A growing horizon can easily be 2 feet deep. These numbers suggest 20 pounds of leaf mold per square foot. That would be a ton of leaf mold for a bed 4' wide by 25' long. This would correspond to a water holding capacity of 1000 gallons of water.

The fungi that have broken down the leaves will still be active within the leaf mold after you have applied it to your soil. Barren soils are quickly improved as these fungi are added, giving your soil the transportation system for all those nutrients and minerals.

It's hard to find information on leaf mold on the internet. It has not been widely studied. Fungally decomposed leaves, leaf mold, is different than bacterially decomposed leaves, compost. Both types of decomposed material are needed.

They also work well in a deep litter poultry system and I find they decompose quicker than pine shavings, so I'm using them almost exclusively now in my coop.

A slowish composting rate is actually good. It means that you are leaving some Nitrogen in the soil for spring plants to use to grow.
The fungi also uses Nitrogen to multiply their cells. The main reason why they are better is because they can transport nutrients
over large distance (100+ ft) with their root like structures and give it to other trees in exchange for sugar.

You could increase the composting rate by increasing O2, aka turning over the leaves with a fork or putting them in a barrel and spinning it
or with composting worms.

You could increase the composting rate by increasing the N2 by manure, growing fava beans/legumes near it, adding green leafy stuff, pee, ammonia.

You could increase the composting rate by increasing the amount of fungi or bacteria. Inoculating with mushroom spores, with composting worms, compost. worm tea

i have been reflecting on some observations i made about the graceful ways trees naturally mulch with their leaves.

especially the ~little by little~ way of it, only a small amount of leaves fall at once in a slow continual process. and how this allows a good amount of seedlings and plants below to still grow without blocking them, but supressing growth in other areas.

this naturally works out good with the spacing...only sometimes its good to thin it out little more, and uncover some areas if you are growing plants under trees.

also that a little at a time ~poco a poco~ way is really the way to go.

i tend to get a bit over board when i think of mulching, trying to get as much as possible at once. which hey is great when you can swing it, for cultivating plants in a specific area, but its too much at once and then i get exhausted, or procrastinate, etc. then nothing gets mulched ! cause i dont get the straw or whatever....

and to just try to get into the habit with a couple of times a month just adding a little bit of some kind of mulch. little by little.

What I do is accelerate the process by feeding all the fallen leaves to our worms- you have to be careful that you add water and other materials- torn up soaked egg boxes, newspaper, the contents of your hover, coffee grinds etc, but little wrigglers will turn a box of leaves and the like into usable soil in two to three weeks. The one problem I have found is that any seeds still remain viable, so I am experimenting with cooking the soil in an old satellite dish over a fire to try and kill off the seeds.

The problem I see with cooking the worm castings in a dish to kill viable seeds, is that it will kill all of the micro organisms and worm eggs that make the living soil. I would prefer to not put seeds in the worm farm if that bothered me. Just dont put nasty seed bearers (noxious weeds) into the worm compost and you will be fine. Personally, if a fruit or vegetable started growing in the sheep paddock after spreading my castings, I would see that as a snack to the sheep, not a problem.

One caution with using too many leaves as a mulch layer is creating a mat that restricts oxygen from getting down into the soil and turning things anaerobic. I think a light layer is best. I also like to turn them into the soil when making beds, toss some into the compost pile, but making leaf mold does seem to be the best use of them. Thanks ken for the great informative post.

Last year I laid out the straw and manure from my chickens in rows that I then double dug. I covered the rows with leaves and let them mellow for most of the year. When I got back around to them, the worm population along the rows was incredible. All of the straw and most of the leaves had been completely decomposed and turned into humus and worm castings. It grew vegetables like magic.

This Guy just used a bunch of leaves for sheet mulching. It looks like you need alot!!
The part about the leaves is half way down the page.
Sheet Mulching Article

my soil was heavy clay and I added composted manure and peet moss but it just made it into slippery almost silky heavy clay. So I had some areas of my drive way (not used by cars) that was covered in vine mats that had leaf mold in them. So I cut the mats and shook out the leaf mold and we had about 30 wheel barrow loads. I mixed it in and it really did help with the texture! My plants have taken off!!! The soil isn't the best and it's not as mixed as I'd like because some patches are better than others but things are growing! I've been watering with worm casting tea and I gave them a little plant food. I have whole leaves on top for mulch.

Excellent information! Many thanks...
My neighbor has a yardful of maple trees, and I've been able to help myself to as much as I want the past several years. Getting into leaf mold is the best...she stacks fresh leaves on top of the pile, so I take those first, and use them to put around plants that need mulch. The older stuff...yum, the smell is absolutely phenomenal...I use in my raised beds and outdoor potted plants.

I just raked up and collected leaves from an old logging road on my property that I keep cleared for a fire break. The challenge of doing the Mike McGrath suggested method of shredding fall leaves to compost is not as easy in the Pacific NW, as deciduous trees drop their leaves with the coming of autumn rain. These leaves will likely never dry out enough to be vacuum-shredded, and clog up any such machine I have tried. The reason given by Mr. McGrath (host of You Bet Your Garden podcast and radio show, former editor of Rodale magazine) for always shredding the leaves is that they will mat and become anaerobic. This is part of how trees suppress competition and fire ladder fuels accumulating around them.

It has occurred to me to try using this matting to my advantage as an alternative for plastic occultation tarps (that I refuse to buy or use) by spreading whole-leaf piles where I plan to put a new planting bed or a tree or shrub in the spring. This would seem to possibly be an improvement in Helen Atthowe’s hay-bail prep. In her recent book on growing one’s own fertilizer, she describes how she places the bail where a tree is planned for, and it is left to rot for a few seasons before planting. The deciduous tree leaves would likely have even more beneficial biota and nutrients for a subsequent deciduous fruit/nut tree or shrub than hay or straw. It seems like this must have been thought of before.

What an interesting idea!

It seems obvious, I live in the North East and when fall comes in we have spats of spritzing which holds leaves in place. Physically raking them from their spots, if they had been sitting there, reveals bare soil and the loss of grass. I never appreciated this matting ability because generally the leaves would dry and end up being thrown about by the eventual windy days.

I know they use a tackifier to hold straw to the ground when planting seed, I wonder if there is something green that could be used to encourage intentionally placed leaves to stay at least until the snow holds them in place?