3 Ways That Leaves Can Help Improve Your Soil

3 Ways That Leaves Can Help Improve Your Soil

oak leaves

Are you looking for a cheap source of organic matter to improve your garden soil? Autumn leaves can be gold for your garden – and they’re free!

We have used leaves three different ways to help improve our soil:

  1. Tilled directly into the soil
  2. Turned into compost
  3. Used as a mulch

We use almost every type of leaf that we can find – though we avoid using walnut leaves in mulch, and we avoid adding too many pine needles to our compost pile. Pine needles take a LONG time to decompose, much like wood chips – which I also avoid adding to compost piles.

Pine needles do make a long-lasting mulch, though. We’ve used them as mulch for several years in our blueberry bed, in the hopes that they would make the soil more acid. Unfortunately, they haven’t. I’ve read a few studies that have confirmed that neither pine needles nor other leaves (such as oak) will make soil more acidic. So, don’t worry that using leaves will acidify your soil. They won’t.

Here are a few tips when collecting leaves:

  • When possible, avoid trees that have been treated with pesticides
  • If you will be using leaves in your vegetable garden, you may want to avoid collecting leaves from a yard with dogs, as their feces often gets mixed into the leaves.
  • Avoid collecting walnut leaves to use as mulch – they contain juglone, a compound that can damage or kill many plants. However, composting the leaves will remove the juglone, and the juglone in walnut leaves tilled into the soil should disappear when the leaves decompose.

1)  Tilling Leaves into the Soil

You can increase the organic matter in your soil by tilling 2-6 inches of leaves into the soil in the autumn (a thin layer of compacted leaves or a thick layer of fluffy leaves). The leaves will start decomposing in autumn, pause during the cold of winter, and then usually finish by late spring/early summer – in time to plant summer crops.

You need to allow leaves to fully decompose before planting the bed. Before planting the bed, dig into the soil to see if you can still recognize pieces of leaves. Leaves tilled in the fall may not fully decompose until late spring/early summer the following year, depending on your climate and quality of soil.

If you plant too soon, the partially decomposed leaves buried in the soil can prevent the healthy growth of seeds or young plants (mulch on the surface doesn’t have the same bad effect).

For leaves to decompose, the soil needs to be moist and warm. Leaves can’t decompose in dry, or very cold or frozen soil

Leaves take much longer to decompose in “dead” or sterile soil – soil that doesn’t have abundant soil life. Adding a small amount of manure, compost, or bacterial inoculant may help leaves to decompose in soil that lacks good soil life (bacteria, fungi, earthworms, etc).

Also, adding sources of nitrogen (such as manure, alfalfa meal, blood meal, seed meal, or feather meal) may help to speed up decomposition, but aren’t necessary in healthy soil.

Composting Your Leaves

You also have the option of composting your leaves before adding them to your garden soil. Once fully composted, you can use them in your garden at any time, and plant immediately. I’ve composted leaves three different ways:

Cool compost pile

  • It helps a lot to use a circle of fencing or other material to help contain the pile of leaves
  • Leaves don’t need air to decompose, as fungi is the main decomposer – not bacteria
  • You can pack leaves down firmly as you create the pile – go ahead and tramp them down with your feet!
  • Water the leaves thoroughly as you pile them up – dry leaves won’t rot, and water often won’t evenly penetrate a large pile of leaves. You may want to water your leaf pile during periods of prolonged dry weather.
  • Shredded leaves decompose faster, but it isn’t necessary in order to compost your leaves
  • Allow up to 2 years for the leaves to slowly turn into beautiful leaf mold (compost)
  • The pile of leaves will gradually shrink to a fraction of its original size
  • Be aware that snakes sometimes like to inhabit or lay eggs in leaf piles

Hot compost pile

It is possible to use leaves in hot compost piles – though the leaves should be shredded and well-moistened before adding to the pile. In addition, leaves tend to compact over time and reduce air penetration, so you’ll need to be diligent about regularly turning the pile.

My sister and I have created a compost pile a couple of times with shredded leaves, horse manure, and some blood meal. We turned the pile every week, and harvested beautiful compost in less than 8 weeks.

Worm compost bin

We use well-moistened shredded leaves as part of the bedding in our large worm bin. The worms seem to love it, and we’re able to harvest rich worm castings a couple of times a year.

Worms in leaf bedding

Our worms thrive in bedding made from shredded leaves.

Using Leaves as Mulch

We use leaves as a year-round mulch in our fruit tree and flower beds, and sometimes as a winter mulch in our vegetable beds. They slowly decompose in place over time, often attracting lots of earthworms.

Worm tunnels in soil covered with shredded leaves

Worms thriving in the soil protected with a mulch of shredded leaves.

We strongly prefer to use shredded leaves for this purpose. A thick layer of whole leaves often becomes matted and reduces the penetration of rain and fresh air – though this depends upon the type of tree. Large flat maple or tulip tree leaves mat much more than curled up oak leaves, for instance.

Shredded leaves also tend to not blow away as much in high winds. There’s nothing worse than putting all the work into collecting and spreading leaves for mulch, only to wake up after a windy night and find most of them gone!

Resource: Mulch Materials Research Report

How have you used leaves in your garden? How well have they worked for you?

  • Carol Schwobel says:

    Hi, Debra, I have a small garden that I mulch with leaves every fall and have never tilled. As a result I have few weeds, the garden soil is great, and my veggies grow wonderfully. Now a friend wants to till all those lovely layers of leaves (11 years worth) into my garden soil. I don’t want to break up all the microryze (sorry I can’t spell the word, but you know what I mean) that have been growing all these years. What do you think?

    • Debra says:

      Hi Carol! If your soil is looking soft and loose several inches deep under the leaves, then I would not bother tilling (unless you needed to blend lime or phosphate rock into the soil). Tilling will reduce organic matter in the soil, break up the beautiful soil granulation, and kill some beneficial soil life such as mycorrhizae fungi. If your soil was hard and compacted, then tilling the leaves in might help to loosen the soil faster than leaving them as mulch. But mulching alone often improves the soil a lot over time.

  • Bonny says:

    It is my understanding that it is only the roots that contain juglone. We have used old walnut chips to mulch with and have used leaves in the compost piles.
    Excellent article. Thanks

    • Debra says:

      The roots contain the highest level of juglone, but it does exist in other parts of the tree in smaller amounts, including the leaves. Some plants are very sensitive to juglone, and others are immune. It doesn’t hurt everything. Glad to hear that you have been able to use it OK.

  • Bikem says:

    A question: we have been told by a gardener that leaves from the tree which shed them, if not cleaned up from where they fell eventually “poison” the tree (that plants do not like their own leaves as food) .. we have been letting dried jasmine leaves gather up on the soil for the fall period to protect the soil from freezing in winter.. how true is this theory on plants being selective of food?

    • Debra says:

      I’ve had training as a Master Gardener, and I’ve never heard that. I know of many trees that have been mulched with their own leaves, and the tress are growing just fine. That occurs naturally all the time. I wouldn’t worry about it.

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