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Which Leaves Are Not Good for Compost?

While most of us with compost bins or piles generally know not to compost things such as dairy, bones, and meat, what about the less obvious ones? For example, are there are types of leaves that aren’t good for compost? I was curious to learn more about this, so I did some research. Here’s what I found.

Avoid composting leaves from black walnut and eucalyptus trees, as these contain natural compounds that will keep seeds from sprouting in your garden. You may also want to avoid waxy leaves like oak, beech, and holly because they have high lignin content and take a long time to break down.

However, if you’re not worried about herbicidal compost or tough leaves, there’s no limit to how you use leaves in your compost. Although, there are some best practices you may want to consider. Let’s find out how to perfect your leaf composting game! 

Which Leaves Should Not Go in the Compost Pile?

a mix of leaves in a compost pile

Generally, avoid leaves that are higher in lignin as these leaves can take 2-3 years to decompose. Instead, use light, papery leaves like maple, ash, or mulberry. These leaves will decompose quickly and provide a good source of carbon and trace minerals for your compost.

All leaves will eventually break down in the compost pile, given enough time and the right conditions. However, some leaves will break down faster than others. 

In contrast, thick, waxy leaves like oak and beech will take longer to break down, sometimes 2-3 years. They’ll decompose eventually, but this can become inconvenient if you want to regularly harvest your compost for your garden.

As mentioned, you should also avoid composting leaves from black walnut or eucalyptus trees. 

These both contain naturally occurring herbicides that can survive the composting process and stop new seeds from sprouting. This is the tree’s natural defense mechanism to keep competing trees from growing near it and sucking up all the nutrients from the soil. 

You could still compost these leaves if you don’t plan to use the finished product to fertilize young, delicate seedlings in the garden, but it’s easiest and often best to avoid them.

Can You Put Fallen Leaves in Compost? 

Fallen leaves are easy to obtain and can be added to compost piles, but you should consider where they came from. Some leaves can contain chemical herbicides and pesticides, which can be harmful to organic gardens. Additionally, some leaves can introduce mold or disease. When in doubt, research the source thoroughly.

Generally, fallen leaves are a great addition to your compost pile! When the leaves fall in autumn, they start to decompose as soon as they hit the ground. 

By adding them to your compost pile, you’re just speeding up that natural process and using it to your advantage. 

Decomposing leaves can be added to your compost at any stage of this process: as whole leaves, partially decomposed, or fully-formed leaf mold. 

You can even use fallen leaves that have been sitting around and decomposing for a few months. Because of their high carbon content, when leaves decompose on their own, they turn into what is called “leaf mold”, rather than compost. 

As they decompose, leaves are broken down by beneficial fungi and bacteria. The result is a mineral-rich substrate that can hold onto more moisture than plain soil.

Are Brown Leaves Good for Compost?

brown leaves decomposing on the ground

Brown leaves are great for compost. Many times, much of a compost pile is made up of “green” materials that need to be balanced with “brown” materials such as leaves. Leaves are an excellent source of carbon-heavy “browns” to balance the nitrogen-heavy “greens” like kitchen scraps.

The only thing to keep in mind when composting a lot of leaves at once is that too many browns can slow down the composting process.

This is fine if you don’t mind utilizing the slow composting method where you set it and forget it, but you may want to use a different strategy if you plan to harvest compost for your garden with a quicker turn-around-time. 

While dead leaves are considered browns, green leaves are considered, well, green. You should always strive for a 4:1 balance between your browns and greens in your compost. 

Many folks will have an extra bin or area next to their main compost pile to store extra browns like dead leaves for times in the growing season when carbon-heavy materials are scarce. 

Layering last year’s brown leaves with fresh, green grass clippings during the summer is a recipe for a successful, fast, and hot compost! 

3 Ways to Decompose Leaves Faster

Maybe you have some large trees near your house that produce a lot of leaves in the fall. And they probably won’t all fit in your compost bin! So, how can you get them to compost faster?

Here are three tips for you to turn your leaves into black gold ASAP! 

1. Shred Them to Increase Surface Area

There are other ways to shred the leaves, but using a lawnmower gets the job done easily. If you have already raked the leaves into a pile, start mowing on one edge and just work your way all across the pile. 

Make sure the leaves are dry before you do this, though. Wet leaves don’t shred as well, and they can jam the mower blade.

This technique works well even if you haven’t raked the leaves into a pile. Just mow the lawn as normal, leaves and all. When you’re done, the grass and shredded leaf blend will compost beautifully. 

2. Keep Them Moist

All materials need proper moisture to compost, and leaves are no exception. Dry leaves simply won’t decompose since beneficial, composting microbes live in moist environments. 

To speed up your leaves’ decomposition, you should water your compost thoroughly. 

Your compost pile should be about as damp as a wrung-out sponge: moist to the touch—but doesn’t drip when you squeeze it.

Be aware that if your compost bin is on the ground underneath a tree, that tree’s feeder roots will find their way into the bottom of your compost and suck away moisture and nutrients. 

You may end up needing to water your compost more often if this is the case. 

3. Make a Hot Compost Pile

If you don’t mind waiting a few seasons, you could compost your leaves on their own to make leaf mold. However, if you’re impatient, you should consider building a hot compost pile. 

This is different from the standard slow, or “cold” composting system where you let brown and green materials pile up and decompose slowly on their own.

With a hot composting system, you start with an empty bin and fill it up all at once. The microbial activity will cause the pile to heat up to temperatures between 135°F and 160°F.

Hot composting requires more attention and work since you have to turn the pile regularly.

Here’s a quick guide to starting a hot compost pile:

Materials:

  • A compost bin at least 3’x3’x3’
  • Enough brown leaves to fill the bin about ¾ 
  • Enough greens to fill the bin about ¼ 
    • Coffee grounds and grass clippings work great 
  • Pitchfork or similar tool for turning
  • Composting thermometer 

Step 1: Fill the bin with alternating layers of leaves and greens. For every six-inch layer of leaves, put in two inches of greens. This will get your compost close to the ideal ratio of carbon to nitrogen. Because it’s impossible to know the exact carbon: nitrogen ratio within each ingredient, your pile may not be perfect at first, but it’s easy to make adjustments in step two. 

Step 2: Monitor the pile’s internal temperature. If you don’t have a compost thermometer, it’s not the end of the world, but temperature indicates the best time to turn the pile. Once you get the compost going, the temperature will climb for a few days. Once the internal temperature starts to cool down, usually after about a week, it’s time to turn the pile. 

Step 3: Turn the pile. Using your pitchfork or shovel, remove the compost from the bin. Then put it all back in! When you do this, place the less decomposed material from the outside of the pile into the center so it gets a chance to cook. This is also the best time to adjust the balance of materials. 

Add water if it looks dry, and add some more leaves if it stinks or is too wet. Add some nitrogen (AKA greens) if it doesn’t seem to be getting hot enough. 

Step 4: Repeat steps 2 and 3 for about a month. Keep monitoring the temperature and turning the pile until the original materials are unrecognizable. 

Step 5: Cure the compost for a couple of weeks. Let it sit and cool down for a couple of weeks before using your new compost in the garden.

Bonus Tip: Use Urine!

Because of its high nitrogen content, adding urine is a great way to speed up the composting process for a carbon-rich material like leaves!

If you’re interested in learning more about how urine can benefit soils, you can check out my recent post: “Is urine good for citrus trees?“.