Meleah MaynardUse your fall leaves to build healthy soil

We have two big, old oak trees in our yard and every fall, up until a few years ago, we would  spend our October and early November weekends raking and bagging and raking and bagging until our hands blistered. Then, we would drag all those bags, bursting with leaves, to the curb to be hauled away. Every now and then, I noticed that someone would pull over, load our bags of leaves into their car and drive off. Why in the world would they want our leaves? I wondered. I soon found out.

For gardeners, or anyone with a lawn, really, fallen leaves are nutrient-rich, soil-building treasure—and they’re free! According to Mark Keaton, staff chair for the University of Arkansas Division of Agriculture, fallen leaves contain 50 to 80 percent of the nutrients trees extract from the soil during a growing season. They’re a particularly good source of nitrogen, offering anywhere from 1 to about 2 ½ percent nitrogen as they decompose.

What in the heck does that mean? Okay, figure that if a tree’s leaves offered 2 percent nitrogen it would take 100 pounds of dried leaves per 1,000 square feet to provide 2 pounds of nitrogen.That’s all the nitrogen 1,000 square feet of turf grass should need for a year, and it’s also about the right amount for a garden bed of that size, too.

But that’s not all. Research conducted by Alexander Kowalewski at Michigan State University has shown that using maple and oak leaves as mulch can help control dandelions in Kentucky bluegrass. Seriously! Go here to read that study. Unlike past studies in which leaves may have contained some pesticide residues, researchers at Michigan State used only pesticide-free leaves in their tests. And that reminds me to point out that it’s a good idea to avoid using anything but pesticide-free leaf mulch on gardens where edibles are grown.

The only hitch in this free fertilizer, and possibly weed killer, bonanza is that you need to mulch (which pretty much means shred) the leaves before you spread them on your lawn or garden. Whole leaves tend to mat down and hold moisture, causing mold and rot issues. Maple leaves are among the worst offenders because they’re so flat. Oak leaves are wavier, so they don’t mat down as thickly, which is good. But it’s still better to mulch all of the leaves you want to spread on your lawn or garden. Leaves break down faster when they’re mulched into small pieces, and they need to break down in order to make the nitrogen they offer available in the soil.

You don’t need any sort of fancy machine to mulch leaves. A regular old, cheap lawnmower will do just fine. You can watch this video we made at our house to demonstrate how to mulch leaves with a mower. Or you can just read the instructions I’ve written in the post below.

To mulch your leaves, rake a big bunch of them into a pile of manageable size. Width isn’t a problem, but the pile shouldn’t be too tall since you have to drive the mower over it. PUT ON YOUR SAFETY GLASSES, OR SUNGLASSES OR SOMETHING because sticks and little rocks and stuff can fly all over the place. Start your mower and drive over the pile slowly so you don’t clog the mower and bind the blade, causing it to shut off. (This is far more likely to happen if the leaves are wet or slightly greenish.) I tip the handle of the mower to raise the front up a bit as I go over the pile, kind of like the mower is chomping down on the leaves.

Once you go over the pile, shut off the mower and rake all those mulched bits back into a pile and mow over them again. I usually need to mulch a leaf pile three times to get pieces down to a good size, which is about the size of a $1 coin or smaller. You’ll notice that the leaves blow all over the place as you mulch with the mower. Some will land in great spots and you can consider those happy accidents. The rest will have to be spread. Rake mulched leaves into place around your plants to a depth of 3 – 4 inches, half that for the lawn. Or, if you need to move the leaves to different spots, use a snow shovel to scoop them up and dump them into a wheelbarrow that you can push around and from as needed.

Yes, you’re right, many of those leaves are going to blow away. To keep that from happening, I sometimes mix shredded leaves with a little bit of compost, or toss a little compost on top of the leaves as I go. You could also just spread the leaves on a little thicker, figuring some are bound to stick around. If this lengthy explanation has left you thinking you’d best just continue bagging your leaves so you can have some time left to live your life, I hear you.

But, chin up. The good news is, you don’t need to mulch every fallen leaf to make a difference in your gardens over time. Just do a small patch this year. Next year, do another small patch. You’ll be amazed how quickly your grayish, hard-as-cement soil will come around and become rich, dark and crumbly. Why leave all that soil-building treasure at the curb?

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Meleah Maynard

About Meleah Maynard

My name is Meleah Maynard and I garden in crazy-ass cold, zone 4 Minneapolis, Minnesota. My first book, co-authored with Jeff Gillman, Decoding Gardening Advice: The Science Behind the 100 Most Common Recommendations, was recently published by Timber Press. I don't have a hort degree. I'm a longtime journalist and master gardener who loves asking people questions, doing research and learning something new every day. I hope you like my blog here on GardenDrum and you read my full blog at Everyday Gardener

2 thoughts on “Use your fall leaves to build healthy soil

  1. AliCat on said:

    Hello Meleah
    I have always considered ‘gardeners’ who annually burn their autumn leaves as being totally wasteful. When you consider the mantra of ‘reuse, recycle and reduce’ surely the best form of reusing is to recycle the leaves from your trees. Not only do they provide nutrients, but the soil texture considerably improves. I also mow our leaves so that you get a mix of lawn clippings with the shredded leaves – a magic brew for your garden over winter. Spot on!
    Alison

  2. A great reminder that there is an upside to these yucky windy days we are having lately – lots of fallen leaves. Our eucalypt leaves not always so great for composting … but your shredding idea is a great one …. thank you.
    On the note of burning leaves being wasteful, the ash remaining is useful on a garden or compost, so all’s not lost.
    Julie

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