Steve Hiltner: Leaves Are Nature’s Mulch

Stephen Hiltner
Stephen Hiltner

Each autumn, our streets are dominated by the driving of cars and the great purging of leaves from the Princeton landscape. Highly visible and often noisy, these two activities have consequences that are silent and hidden. The less we drive cars, the fewer invisible global warming gases rise into the atmosphere. The fewer leaves blown into the streets, the less invisible expense to carry them away.

But how does one model more beneficial behaviors? If I avoid running an unnecessary errand, no one sees me not driving the car. If I pile my leaves in the backyard rather than in the streets, neighbors won’t emulate an approach they cannot see.

In addition, there are many fears and rumors associated with keeping leaves on one’s property. Will a pile of leaves attract rats, create odors, catch fire from the heat of decomposition, suffocate the tree roots underneath, or fail to decompose? In my experience, none of these fears are justified. Piled leaves settle and decompose, untended, and within a year produce excellent compost that, if not harvested, will be eagerly gobbled up by invading tree roots.

Leaves are nature’s mulch. They keep the ground cool and moist in summer. Birds search underneath them for food. Fireflies lay their eggs under leaves. “Cleaning” a yard of leaves means cleaning the neighborhood of birds and fireflies.

This year, I have sought to make the invisible visible. To assess best practices, I urged our town officials to document all the costs associated with cleaning up the year-round piling of leaves, yardwaste and brush in the streets. I suggested we demonstrate “leave the leaves” management in the local parks, by mowing leaves back into the turf, and have demonstration leaf corrals homeowners could emulate in their own yards.

Then I realized that, living on a busy street, I could model beneficial behavior right at home. There are now several leaf corrals in my front yard on North Harrison Street. Hidden behind shrubs or out in the open, they easily accommodated all the leaves raked up from the lawn. The one close to the sidewalk is about the size and shape of a wishing well, and if you think about it, a leaf corral is like a well in reverse. A well gives us an ongoing supply of cool, clean water from the giving earth. A leaf corral represents a giving back, a means of steadily feeding nutrients back into the ground from which they came.

To help make visible another hidden, but highly positive legacy, that of Princeton’s visionary mathematician and open space pioneer, Oswald Veblen, I am offering to sell and help install at cost a leaf corral in the yard of anyone who makes a donation of any size to the Friends of Herrontown Woods, the nonprofit working to rehabilitate the historic house and cottage that the Veblens donated long ago to the public trust. This project, too, represents a giving back, to a quiet legacy that so influenced the Princeton we know and love.


  1. Your post is a positive contribution. Because of the “Leaves the Leaves” campaign, I only placed leaves from our front yard out for collection. Our side yard & back yard are leaf covered. We’re looking forward to a more beautiful display of fireflies & healthier grass in summer 2016.

    1. I ‘left the leaves’ in my yard last year, and they shaded out the grass, killing the lawn in some patches. I had to go in with grass seeds this spring to try to fix up the dead bits. If you’re going to ‘leave the leaves’, I suggest running over them with your mower on ‘mulch’ setting. That grinds ’em up into little bits which mulch easily after it rains, and they don’t mess up your lawn. By doing that, we didn’t need the town to pick up any leaves for us this year.

      1. I’ve been urging the town rec department (there’s no parks department) to demonstrate leave the leaves management in town parks, and was glad to hear that they are shifting in that direction this year, mowing leaves back into the turf in some areas. The alternative, blowing leaves into piles and then loading the piles into trucks, then driving the leaves out of town, etc., etc., is far more time and energy intensive, in addition to depriving the parks of the nutrients in the leaves.

        1. Great… maybe those employees will use the time no longer devoted to removing leaves from parks to removing leaf/debris hazards from high traffic areas!!

  2. This doesn’t work for small lots with actual gardens. Leaves shouldn’t be used to mulch flower or perennial beds unless shredded fine. There are some plants that will develop diseases (powdery mildew, black spot) if leaves are left at their base – they are the reservoir for overwintering fungi. The idea of letting leaves remain where they fall is excellent for forests and works for ordinary shrub borders but there is a reason why gardening textbooks tell you to clear debris at the end of the season from anything more elaborate. The leaves do make fabulous compost, especially if the pile temperature gets high enough. But urging us to let them remain where they fall is not horticulturally sound for all situations.

    1. I’ve been gardening for forty years, and know there are many approaches to gardening, and lots of assertions flying around. I agree that some perennials and spring bulbs have a hard time navigating up through unground oak leaves in the spring. So I definitely agree with the need to grind up the leaves, with a lawn mower or reverse leaf blower. The You Bet Your Garden guy is a big proponent of this. My silver maple leaves, on the other hand, are largely decomposed by spring, so not all leaves need grinding. Leaves may harbor fungi, but many of those are beneficial. If there are plants that, oddly, have been bred to be hypersensitive to leaves on the ground, then one approach is not to have those sorts of plants in the garden. I was really surprised to find that oak leaves I raked up in the spring and put into a leaf corral, where surely they decomposed at a low temperature, without any mixing, made great compost by summer’s end. The leaves on the outside of the pile were not decomposed, but inside the pile was a wonderful compost, twenty pounds’ worth. We call it “leaf mold”, using the word “mold” in a positive sense. That story is told at this link: https://princetonnaturenotes.blogspot.com/2015/11/the-not-so-scary-leaf-pile.html

    2. I tend to take a different view on this. Many of my perennials appreciate a ‘blanket’ of fallen leaves above them through the winter. In zone 7, some of them are marginal, especially when we get a cold winter like the last couple. I am quite sure that my chrysanthemums only survived last winter thanks to the thick layer of leaves I left on the beds. (They are still blooming now, and a delight.) Colorful snapdragons are often considered to be annuals in zone 7, but mine get sheltered under insulating leaves and are reliably perennial. Now that I have magic lily planted in my yard, I am taking extra care to leave a layer of leaves for protection. I work with my leaves on the beds, first letting them lie, then lifting and moving them to the compost heap as the season progresses. (often they are mostly mulched by then.) It’s so nice to uncover the first snowdrops, in fact, my ‘Potters Prelude’ is already flowering and I have opened up the bed around the plants so I can check them out every morning before work.

      Powdery mildew is a curse in Princeton, but I tend to think it’s more to do with the humid summers than the winter leaves. I replaced most of my bee balm and phlox with resistant varieties and that solved it. Probably there are some gardeners whose plantings are so sensitive that they will not tolerate leaves. Those gardeners will know what they are doing and lift leaves as appropriate. But I reckon 99% of yards will not be negatively impacted and some, like mine, might stand to benefit from a more tolerant approach to fallen leaves.

        1. Alexi, I’d be happy to have you and anybody else who is interested over in the spring when it is time to put down mulch. 😉 Seriously though, my yard is nothing special right now and it will take me years to get the plantings to mature.

  3. Mr. Hiltner I applaud your efforts & concur 100%. I would further offer that the Township needs to consider the safety hazard created by the leaves piled in the streets, many of which area also approved bike lanes. If one was to place something in the street that blocked car traffic, surely they’d be fined and dealt with by authorities; however, we knowingly instruct & encourage residents to block the bike paths forcing cyclists, many of whom are children biking to school to leave the bike lane & enter traffic to avoid the stockpiles. We cannot have both.

    1. Good point. An industrial leaf vacuum that allowed people to leave leaf piles right ON their edge of their property, within it’s boundary but accessible from the road, should be used. The municipality uses the heavy jaws method for debris & leaves, when there are other, safer, QUIET options for the leaves. The right tool for the job, or a different approach to removal, would be safer.

      1. The borough had a leaf vacuum. It worked on dry leaves but had problems sucking up wet leaves. The town does have a guy raking leaves off the curb into the street, ahead of the Jaw. The caravan includes a guy raking, a Jaw, and two garbage trucks. That’s four workers to do the loose leaf pickup. If the town shifted more to containerized pickup in 64-96 gallon rollcarts, keeping leaf bags and fall loose leaf pickup for the time being, a crew of four would be largely replaced with a crew of two picking up containerized leaves/yardwaste, with a lot less traffic disruption.

        1. We definitely don’t need citizens buying more indestructible weather proof plastic containers. We do need municipal employees who remove or address hazards & a Council able to smartly address root causes. We also need people who don’t overstate hazards to inappropriately feed fear or push agendas that create wasteful spending. I totally give my kids (& myself) permission to avoid hazards by biking on a sidewalks or stopping until traffic passes… we’ll probably end up biking with cameras/bike cams to defend ourselves in court, when wacky policy makers decide to fine us for that.

          1. According to the mayor, biking is legal on sidewalks except on the town side of Nassau Street downtown. Plastic can be a useful material, and I’m not sure if suggesting a solution represents pushing a personal agenda.

            1. Hey Steve, My “personal agenda” comment wasn’t about your desire to sell & install leaf containers. I sincerely sent you a compliment for trying to do good & believe in supporting all community go-deed-doers who live & work in Princeton. We agree that suggesting solutions & alternatives is always a good thing when concerns arise. I was actually referring to the agendas pushed by Council that expand government & taxes, after they ignore cost, comments & better solutions. For example, you can view a 67 page “Plastic Bag Fee – Legal Opinion” on the princetonnj.gov website. It was prepared for paid municipal staff members to review, in advance of creating a legal ordinance. This expensive legal work was authorized despite wise advice from Board Members serving Princeton to the contrary & despite the fact that an Act legislating plastic bag use is already pending at the State level. So, I see Council’s expenditure of paid staff time & taxpayer money on this work as an expensive “push”, to advance the agenda of friends, & a push done so while ignoring advisors & activity in the State. With this year’s dramatic increase in local summonses, fines routinely suggested, & bag fees pending, “punishment” to modify behavior as people go about their daily lives is the clearly the draconian technique of our local governing body. You brought up biking, so with tongue in cheek I imagined our kids arriving home with summonses for biking too… but, I am seriously concerned about the lack of wise & creative problem solving in Princeton. At least you are trying a solution on your own, sharing it, & not suggesting fines or ordinances demanding receptacles that punish … good for you!

  4. I was under the impression that all leaves go to the ecological facility in Lawrenceville where they are properly composted. Several residents then pick up the compost over the course of spring and summer and put it into good use in their yards. I wouldn’t exactly refer to this as wasteful.

    1. It’s wasteful if one considers the amount of time and energy spent to collect, transport, grind up, turn, load, and then retrieve nutrients and organic matter that could have been easily utilized directly by the homeowner, without the $800,000 annual public expense and consumption of fossil fuels.

      1. FYI, I mow my leaves back into the grass because it improves the soil.

        someone rakes their leaves by hand and puts them in a pile and consumes
        them all by themselves, fossil fuels are consumed. If one runs over
        the leaves and mulches them into the lawn, fossil fuels are consumed.
        You could make an argument that centralizing the processing of
        brush/leaves is more efficient and leads to less fossil fuel consumption
        overall. Those large processing machines consume a lot less gasoline
        than the residents of Princeton and Lawrence would each individually
        operating lawn mowers to mow them into the lawn.

        ecological center does not just deal with leaves. They also process all
        kinds of branches and stumps that homeowners do not have the ability

        Unless you are suggesting we go back to the
        1800s and do everything by hand, the cost of processing the leaves and
        the benefits that come with doing so are of minimal cost to the
        environment and more likely, the best option. We also get the added
        benefit of having essentially a supply of unlimited natural mulch and
        high quality compost to use on our properties.

        A recycling operation should never be characterized as wasteful.

        1. It’s worth having some back and forth, because this is a commonly held view. If everyone individually took their leaves to the composting center, then the town’s centralized collection would be more efficient by comparison. But if it takes about the same amount of fuel to blow leaves to the curb as run over them with a lawnmower, then all the additional fuel for hauling and composting and hauling back is an additional consumption and unnecessary. We think of those large composting operations, like the Lawrenceville Ecological Center, as being “green”, but they’re actually very energy-intensive. Though there will always be leaf collection of some sort, and central composting, we’re spending hundreds of thousands of extra dollars to collect and process leaves from very large lots that could easily accommodate them, and people on small lots can do a lot to incorporate most leaves into their yards.

          Brush collection and composting at the Ecological Center is useful, given how slowly it decomposes in the yard. I find it easy to make a brush pile in a back corner for habitat, thus avoiding even having to put brush out.

          1. To each their own. I agree, mulching is the best option, but I do like
            the brush pick up, and in a lot of cases, I like to avoid letting leaves
            accumulate because it can do damage to the lawn and other plants.

            That being said, I would never take measures to ensure that people have to keep the leaves in their yard.

  5. I appear to be the only on on my ENTIRE street of Hawthorne Avenue (near the Westminster Choir College) that mulches the leaves on my property.

    1. Yes. This really speaks to the fact that utilizing leaves in the yard is essentially invisible, and thus hard for neighbors to emulate. What’s highly visible is the piling of leaves in the street, so neighbors take their cue from that and do the same. One approach to changing this imbalance is to integrate leaf corrals into front yard landscaping, and also for the town to make available 64-96 gallon rollcarts for containerized pickup, piggy-backing on existing leaf bag pickup. More on this at this link: https://princetonprimer.blogspot.com/2015/12/the-cost-of-free-leaf-bags-in-princeton.html

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