How to Make Leaf Mold

Start with the fall leaves from around your (and/or your neighbor’s) yard. Only use leaves from yards that don’t use synthetic chemicals on their lawns for contamination reasons.  Some people don’t consider chemical contamination to be a significant concern with leaf mold because the lengthy decomposition time allows for chemicals to break down as well. But why take chances when leaves are so plentiful? Beyond chemical contamination, leaves that have been raked into the street for pickup may contain sand, fuel, or oil residues, so it’s not a good idea to just drive around and pick up leaves that have been left by others on the curb. That said, if possible, you may want to gather a variety of leaf types for your pile since different leaves bring different concentrations of minerals to the mix. It might be helpful to think of your leaf pile as a mixed leaf salad.

Now ensure that the leaves are thoroughly moistened (but not soaked). Dehydrated leaves have lost most of their nitrogen, which hinders the decomposition process. If you can, rake up your leaves and get them started in your pile before they have time to dry out and lose the activating nitrogen!

You can also speed up the rate of decomposition by starting with smaller leaf pieces. A quick and effective way to do this is to run a lawn mower over your leaf pile a few times.

Leaf Mold Bin Method
Make a leaf mold bin or “cage” from stakes and chicken wire. It should be a minimum of 3 ft square (or diameter), but larger is better for leaf mold — a 5 or 6 foot square allows for good moisture and heat retention, and will take about 25 bags of leaves to fill. Line the sides (not the bottom!) with recycled cardboard and/or black plastic.   Fill the bin with leaves: Pack them as tight as you want. Moisten them, and then cover the top of the pile with plastic, a tarp, or a piece of carpet (though I’ve heard there are some nasty chemicals that can leach out of carpet, so take that into consideration). The cardboard, plastic (or tarp) make it easier to maintain the moisture level of the leaf pile and keep it from the drying effects of wind. Contact with the soil is helpful to the process  (worms will move into the pile while it’s working) which is why you don’t want to line the bottom of the bin. Check the moisture level occasionally during dry periods, add water if necessary, and turn the pile periodically to keep the moisture evenly distributed and increase contact with the soil.  The volume of a full bin will reduce considerably over time. After 6 to 12 months, the bottom of the pile will be useable leaf mold but the rest of the pile can take more than a year to complete, so you may want to plan for multiple cages or bins and turn the piles by transferring from one bin to another.

Leaf Mold Plastic Bag Method
Place wet/moist leaves into black plastic bags. Seal the bag and then cut some holes or slits in the bag to allow some air flow (poking the bags with a pitchfork works well).  Check the bag every month or two for moisture, and add water if the leaves are dry. Once in a while, turn the bags over and/or give them a rough shake to keep moisture evenly distributed. When the leaf mold freezes, break it up as much as possible. Since you may have several years worth of leaf fall in various stages of the process, it can be helpful to mark the bags somehow to determine which bags will be ready, when. A handy side benefit of this method is that you can also use the stockpiled leaves that are partly decomposed as a “brown” component of your regular compost.

Some sources suggest adding a few grass clippings now and again to boost the nitrogen level of your leaf piles to speed the leaf mold process. But in doing this you are actually changing the decomposition method to “composting” (bacterial) from the intended molding process which is fungal. Add any greens whatsoever to your leaf pile, and you have instantly switched from making leaf mold, to making compost…

Your leaf mold is “done” when it is  soft, crumbly, and the individual leaves aren’t recognizable. Harvesting leaf mold is as simple as shifting your cage or bin and moving the rich humus to the place of your choice. You will end up with an amount of leaf mold that is approximately 20% of the original volume of leaves that you started with.