What to Do with Raked Leaves: Free Natural Fertilizer

A citizen-science project reveals the "unbe-leaf-able" soil benefits of composted leaves and twigs.

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by Adobestock/Victoria
Add composted leaf litter to your garden crops.

Wondering what to do with raked leaves? Turn it into composted leaf litter, or leaf matter, and read on to see how one small farm put this natural fertilizer for plants to the test. 

At Peach Ridge Farms in Grand Rapids, Michigan, we know, “If the soil ain’t happy, ain’t nobody happy!”

Since 2002, we have used tried-and-true methods of environmental stewardship. We use inexpensive and manageable practices, working with the soil to make it better each year. We’ve seen how the plants love it. This year, our kohlrabi was early and already the size of cabbages! We’ve also noticed how garlic grown with our secret ingredient is giant compared with the same garlic planted without it. It’s proof that soil management matters.

Our secret is adding leaf matter (defined here as chopped-up twigs and leaves), or “leaf litter,” in the fall. Some people wonder what to do with raked leaves in the fall. We let it set over winter, and then we till it into the soil in early spring as free natural fertilizer for plants. Shhh! Don’t tell anyone, OK? Last year, we added over 174,000 pounds. In many areas, it was 4 feet high! Needless to say, these leaves were not all from our backyard. The truck delivering these leaves was so weighed down that it got stuck coming into the wet field. We had to use a tractor and chain to get it free.

todd quick seated beside an older man, his father, beside a basket of greens.

What if the benefits of composted leaf matter were only speculation? Maybe we were trying to make the facts fit our assumption that we were onto something with our sustainability. After all, every aspect of farming is affected by a plethora of causes. We decided to put fertilizers to a scientific test.

Ready, Set, Test!

First, we needed money for this experiment. We applied for and received a USDA-NIFA grant from North Central Region SARE through the University of Minnesota to purchase seed, garden hoses, gas for the greenhouse, and other necessary supplies. As part of our preparations for the experiment, we did a survey of the scientific literature. We found two academic articles about using leaf matter, but none about its effect on basil. Like most academic articles, they have fairly long titles; one, for example, reads, “Effect of Leaf Mold Mulch, Biochar, and Earthworms on Mycorrhizal Colonization and Yield of Asparagus Affected by Fusarium Crown and Root Rot”!

Our side of the deal was to keep our Facebook followers up to date on the experiment; to pass out flyers to our community-supported agriculture (CSA) program customers and at our farmers market; and to report our findings at the annual Grand Rapids CSA open house.

plastic containers of lemon basil with a sign labeled

Having gotten the money, we were ready to plant. We planned on growing sweet and lemon basil in three different plots in our greenhouse. The first plot would have soil enriched with leaf matter only, while in the second, the soil would be enhanced by leaf matter and organic duck manure. Finally, the third plot would feature soil with leaf matter and organic chemical fertilizer.

For this experiment, we had several goals in mind: first, to enjoy the flavors of our basil plants; second, to increase our basil harvest; third, to help the environment; and finally, to save some money. We also wanted the results of this experiment to be applicable to small-scale farmers and backyard gardeners.

Basil is a delicious herb. Its smell makes it a pleasure to weed, pick, and just be around. It’s easy to use in dishes such as pesto. It tastes better fresh than as the dried herb you can get at the store. It also has low rates of disease and is highly nutritious. To boost the validity of this experiment, we planted the sweet and lemon varieties of basil, so we would know that the winner wasn’t just a fluke.

whole stalks of basil in a wooden bucket

How would we test for the winner? We weren’t able to measure flavor or health of the individual basil plants, so our criterion for the winner would be based on the weight of the harvested basil. After all, more basil means the plants grew well.

Part of receiving the grant involved being a responsible steward of the Earth, a goal that matched perfectly with our focus on sustainability. Using leaf matter reduces yard waste. Besides that, we hoped to show that using leaf matter to supplement nutrients in the soil eliminates the need to further add undesirable chemicals. If leaf matter was a good source of nutrients by itself, or in combination with chemical fertilizer or duck manure, we knew we would know our method is truly useful.

Two men stand on the grass with a hand on a sign with flowers creeping up the posts. The sign reads

Regarding money, we wanted to provide basil to customers at a reduced price. Most people have it at home, so we wanted to give them an even better deal. Plus, if the experiment showed leaf matter as a good source of supplemental nutrients for the soil, other farms and individuals could also save the money typically spent buying fertilizer.

May the Best Leaf Litter Fertilizer Win

Here are three fertilizer combinations that we chose to measure in the experiment.

1 Only leaf matter. This is what we generally use at Peach Ridge Farms. By digging topsoil from our fields and putting it in the greenhouse buckets, all six test areas had the same soil.

In the future, we’re planning to test leaf-matter-enriched soil against soil that has not been enhanced with leaf matter.

2 Leaf matter and organic duck manure. Most gardeners have heard of the benefits of manure, but is it necessary in addition to leaf matter? We chose duck manure simply because we have ducks. The manure was aged, so there was no danger of parasites. Aging is necessary when using manure from certain animals. (Read about how to safely age your livestock’s manure.)

3 Leaf matter and organic chemical fertilizer. Commercial farms usually use chemicals, which can have negative side effects, so we avoid these on our sustainable farm. But we were curious as to whether organic chemical fertilizer was necessary. After all, the price of organic chemical fertilizer is considerable, but the chemicals are specifically added to optimize production.

The Experiment Is Afoot

In April 2021, we planted both kinds of basil in seed trays. The soil media we used to fill the seed trays is useful for plants to sprout in but didn’t have any nutrients. This allowed us to divide the basil seedlings evenly among the three areas without affecting the results, instead of just growing whatever germinated in that area.

Finally, it was time to conduct our experiment. We had six plots, each with 25 leftover 2-gallon ice cream buckets. We filled each bucket with leaf matter and soil. In the first area, which had only leaf-matter-enhanced soil, we added nothing before planting and only water after. In the second area, 1 pound of duck manure was mixed with 5 gallons of water and applied to the soil for three days before planting. In the third, 3 ounces of organic chemical fertilizer per quart of water was added every other day for three weeks. This overlapped with planting time, so this was the only area that was fertilized after planting.

a table covered in baskets of fresh produce. There are onions, cabages, tomatoes, and potatoes grown with leaf litter

When the basil seedlings were a week old, we transplanted them from the seed trays to the buckets. We spaced the plants equally and fairly divided the largest and healthiest seedlings among the six areas to keep the experiment as consistent as possible. As the basil grew, we weeded it on a weekly basis.

Customers coming to our farm are used to harvesting herbs from our greenhouse, so we kept record of what was taken throughout the growing season. Finally, the day came to measure what remained.

The Winners: The Best Natural Fertilizer for Plants

So, what did we discover? There is still a lot to learn, much of which goes against conventional wisdom. Our results suggest that duck manure may be an incomplete fertilizer for sweet basil. Now, I’m curious about the timing of when to add duck manure to the soil — whether it depends on the plant or how often the manure is applied. That’s another option for future study. Plus, we learned that some but not all varieties of crops do better with organic chemical fertilizer. That’s yet another future topic to find out if there’s an ideal amount of nutrients for plants, after which more nutrients actually prevent optimal growth.

Two charts, each with a y axis labeled

Most importantly for us, this experiment shows that leaf matter by itself can give plants the nutrients they need. The sweet basil grown in only leaf-matter-enriched soil did almost as well as the sweet basil grown in soil with leaf matter and organic chemical fertilizer. Intriguingly, the lemon basil grown in the leaf-matter-enhanced soil did the best of all the lemon basil. Our hypothesis was supported. All these years of filling the fields with leaves have been a wise move!

The Takeaways: What to Do with Raked Leaves

It’s easy to reuse yard waste for healthy soil by composting leaves. They can be dumped in the fall and left to sit all winter. Use a rototiller or a hoe to chop them up and mix them in the soil before planting. Your plants will enjoy soil with extra nutrients, while you save money and feel great about helping the earth.

Peach Ridge Farms is a sustainable farm located in Grand Rapids, Michigan. We have restaurant sales, commercial accounts, charities and schools, classes, and CSAs.