Last fall I was ahead of schedule and was able to do spring cleaning in the fall. Cleaned up the beds and then topped off with 3-4" of shredded leaves. Basically, as the leaves fell, I shred them and filled the raised beds with the leaves. Rain would wet and compact the layer and I'd repeat throughout the season. I didn't really know what to expect. I hoped the shredded leaves would insulated the soil underneath so organisms could continue to thrive. I even put very hastily built, not expected to survive long cold frames with simple clear plastic over a couple of the beds. Those cold frames have since crashed and burned with the snow.

I've found that shredded leaves are a great insulator. The top 1" or so is loose and thawed but below that level is frozen. Not sure how far below that is frozen as I didn't dig down below. Still want to compare the bed to one that I left alone as a control, but as of right now, the shredded leaves did not appear to keep the raised bed from freezing. Maybe next year I'll fill in between the beds with leaves as well though two of them have straw bales between them and didn't appear to be in any better condition. I'm going to build better cold frames or low hoop frames and get 6mil plastic next year which should work much better.

You only made one mistake, and it impacts oxygen, which in turn impacts the depth of oxygen into the soil, which of course impacts the depth of oxygen dependant activity in the soil to the degree that is does or does not impact your plants. A lot goes on in those upper layers where heat and the atmosphere penetrate the upper few inches of the soil horizon.

You made the leaves smaller.

Two things would have happened if you had not.

1) As you seek an insulator, the forest floor has worked it out to have loose , large leaves in fall with plenty of air pockets. Here is where insulation comes in. Loose puffy parka jackets, fiberglass batt insulation etc are all trapping air. Conductors are solid, insulators puffy.

2) Those loose leaves get air as close as possible to the soil, thus as deep as possible into the soil. By matting them, and prematurely wetting them possibly, you have not only reduced insulation prematurely across winter, but increased to some degree a suffocation of the soil below.

Solution: Study the process of the forest floor. There is a fall-winter-spring timing already worked out in the way leaves collapse and become compost. Be lazy. Getting the leaves to the spot was good enough. Do not overdo the pile height either.

While I agree with Dirtmechanic that the trees put the leaves where they will do the most good, and we should appreciate them where they lie... Personally I wouldn't expect the soil to stay completely unfrozen.
That isn't how insulation works.
What the leaves do is keep the soil frozen after it eventually does freeze, and this prevents frost heave... which can do some damage...
insulation levels out the temps that the plants have to deal with.
too much up and down of temps can stress the plants.
And...
The leaves on top of the soil should help prevent a really deep freeze...

Maybe try an auger to compare depth of frozen soil?

thommesM said:Last fall I was ahead of schedule and was able to do spring cleaning in the fall. Cleaned up the beds and then topped off with 3-4" of shredded leaves. Basically, as the leaves fell, I shred them and filled the raised beds with the leaves. Rain would wet and compact the layer and I'd repeat throughout the season. I didn't really know what to expect. I hoped the shredded leaves would insulated the soil underneath so organisms could continue to thrive. I even put very hastily built, not expected to survive long cold frames with simple clear plastic over a couple of the beds. Those cold frames have since crashed and burned with the snow.

I've found that shredded leaves are a great insulator. The top 1" or so is loose and thawed but below that level is frozen. Not sure how far below that is frozen as I didn't dig down below. Still want to compare the bed to one that I left alone as a control, but as of right now, the shredded leaves did not appear to keep the raised bed from freezing. Maybe next year I'll fill in between the beds with leaves as well though two of them have straw bales between them and didn't appear to be in any better condition. I'm going to build better cold frames or low hoop frames and get 6mil plastic next year which should work much better.

How cold does/did it get there?
If you get below zero your ground is going to freeze unless you have leaves , not shredded at least two feet deep and for all practical purposes a lot more.

As Stone said the leaves are supposed to stop the frost from going deep.
Expert rose gardeners up here say you are not supposed to cover your roses UNTIL the ground has frozen, not before.
Now this is partly for disease control but that frost layer also acts as a barrier..
For roses and it works the same for anything , Oak leaves are those that will compact the least and remain dry offering the insulation similar to a down coat.

RpR said:
For roses and it works the same for anything , Oak leaves are those that will compact the least and remain dry offering the insulation similar to a down coat.

I disagree. Sycamore leaves are WAY better at retaning their (curly) shape during winter.

Arico said:
I disagree. Sycamore leaves are WAY better at retaning their (curly) shape during winter.

There are no sycamore (plane) trees in my area.
Oak leaves do not curl.
Oak leaves are very slow to break down due to their acid content .

My experience with oak leaves (I'm on wooded property with a few different oak types) is that once they get snow on them, they flatten out into a wet mat. Oak leaves are pretty dense and waxy and don't readily break down over a winter here.

I have a lot of oak leaves in my own yard, and a lot of yards in my neighborhood do also. I love to use the whole leaves in paths and out of sight beds. For my seedling beds and other flower beds I much prefer to use shredded oak leaves. They make a very nice looking mulch when shredded. Large whole leaves often tend to mat and block water from penetrating them. Shredded leaves allow the rain to penetrate and they stay in place so much better when shredded. Even when shredded oak leaves take a long time to totally decompose, but I am to the point in my gardening now that if it takes two years that is fine, I just try to keep piles at different stages, some for mulch, some for compost or just leaf mold.
Now if I had my choice I might prefer to use much smaller softer leaves that break down much quicker(I do pick up quite a few of those also) for the beds, but I like that the oak leaves are tough and last a long time in the paths. I guess here in Alabama the leaves are more important as a sun blocking insulation in summer than a ground freezing preventing type insulation in winter.

@Dirtmechanic - you remind me of someone I knew on CompuServe's Gardening forum a long time ago. I shredded leaves for my compost pile and tried to rush that process and she really questioned why. LOL. Yeah I don't have a lot of space so I needed to get compost finished faster than not. She also suggested that the whole leaves would help maintain oxygen. I totally agree with your philosophy and am trying to adapt to what nature does for the most part. Next year I doubt that I'll add leaves to the top of the raised beds. I might have enough compost to add a layer. I might put a layer of whole leaves on top to insulate, but raised beds have side and there's no real protection from the cold on the sides. :(

@stone I think you're right. The top layer of leaves were frozen, with a layer of unfrozen below, but then the ground appeared to be frozen below that. Maybe the soil got cold from the sides of the bed since the beds are raised and the sides didn't have any protection.

We have mostly oak leaves in our subdivision but not all. For the last several years I have shredded leaves around the oak trees. I get neighbors' leaves and shred them. Some maple, other varieties as well but mostly oak. I put a 4-5" layer around the oaks. Rain flattens the shredded leaves but not into a mat. The shredded leaves are always broken down by mid summer. I'll have to take pictures to document the stages. The oaks love the loam.

Why wouldn't you want to rush the process of breaking down leaves? That's what compost is: a rushed decomposition process. Your chipper/shredder is an awesome tool for composting. Save your grass clippings throughout the summer. Add grass clippings to your leaves in the fall as you run them through the shredder. If you get the moisture right, you'll get hot compost. Conversely, if you save some shredded leaves over the winter, add them to fresh grass clippings in the spring and run the mix through the shredder. This will work even better.

In my experience, mulching, or covering the soil of the annual garden isn't really desirable. It seems to create habitat for pests, and I don't really see the benefit. I don't want the soil insulated in the spring because where I live the frost would stay in the ground until June if it was covered with dry leaves. Covering perennials with leaves over the winter is great though. You'd want your shredded leaves to be on the dry side, and not too fine, because I think the covered plants still need to breathe a little bit.

The shredded leaves was an experiment for me. Right NOW, I'm considering it a success, in teaching me that I probably don't ever want to do it again on the raised beds. LOL. I'll see what I think this weekend. If I see ONE worm, I'll say YEAH! I've pulled the leaves off of a couple beds, put some compost on one, and will be buying some compost for the others in the next day or so. Ideally I'd rather put a couple inches of compost on top of the beds in the fall, but I didn't have enough for all of them. It looked nice though. LOL.

I'm going to try some hoop cover gardening at the end of this season. Basically, a hoop cover with plastic on it. Try to extend the season a little bit. Need to research heat sinks to see what might work best. I don't expect great results but next spring, the beds should warm up faster and I might already be planted in the ones that have covers.

thommes, I've got a big layer of shredded leaves on my garden, and chickens who love to scratch in them. Looking really closely, I find tiny worms in the very wet leaves, and big worms in the soil underneath if I lift up a forkful. They may be in yours.

I'm hoping so. I'll find out tonight. I'm gonna finally get going on the season. I've noticed a lack of worms in the raised beds, but I have some under the weed blocker that I've been pulling up.

So... I went out and removed the 3-4" layer of shredded leaves in another bed. The soil was cold. Not frozen, the leaves were wet, like a dog. Yeah I'm bad at this game. However, at the bottom of the leaves, or the top of the soil, I happened to notice, worms! This bed had absolutely NO protection of any kind from the elements. I didn't play in the bed that has had plastic on top of it, or the bed that had a row cover with fleece on top for the last two-three weeks. I really want to see the bed that had the plastic on top since it stayed the warmest. I'm still happy to see worms in the soil. I don't remember the last time I saw a worm in the beds.

Worms love cardboard...I'm just saying...

Rubi said:Why wouldn't you want to rush the process of breaking down leaves? That's what compost is: a rushed decomposition process. Your chipper/shredder is an awesome tool for composting. Save your grass clippings throughout the summer. Add grass clippings to your leaves in the fall as you run them through the shredder. If you get the moisture right, you'll get hot compost. Conversely, if you save some shredded leaves over the winter, add them to fresh grass clippings in the spring and run the mix through the shredder. This will work even better.

In my experience, mulching, or covering the soil of the annual garden isn't really desirable. It seems to create habitat for pests, and I don't really see the benefit. I don't want the soil insulated in the spring because where I live the frost would stay in the ground until June if it was covered with dry leaves. Covering perennials with leaves over the winter is great though. You'd want your shredded leaves to be on the dry side, and not too fine, because I think the covered plants still need to breathe a little bit.

What Rubi said..... I have 20 Maple trees in my backyard which means ALOT of leaves I pick up. I do this with a lawn vac pulled behind my garden tractor. Tractor mower chops them up and the leaf vac's impeller chops them even more. I have been dumping them in my woods for years and I have a huge pile of "leaf dirt".

In the spring I mix this "dirt" in with last years growing soil and compost from my barrel tumblers. Very good results. No mulching for me. I grow in 95% containers (4'x4') and strawbales.

Fins59 said:

What Rubi said..... I have 20 Maple trees in my backyard which means ALOT of leaves I pick up. I do this with a lawn vac pulled behind my garden tractor. Tractor mower chops them up and the leaf vac's impeller chops them even more. I have been dumping them in my woods for years and I have a huge pile of "leaf dirt".

In the spring I mix this "dirt" in with last years growing soil and compost from my barrel tumblers. Very good results. No mulching for me. I grow in 95% containers (4'x4') and strawbales.

We call that dirt leaf mould and just let me know when it's time for me to come get some. ;) Hats off to you!