Category: Town of Vienna, VA

 

My town goes to great effort and expense to collect and dispose of leaves each fall.  Homeowners are instructed to rake their leaves to the curb.  The leaves are vacuumed up, trucked off, and hot-composted.

To me, this looks increasingly like an anachronism.  It’s one of those practices that was a point of civic pride 40 years ago, but which today appears to be a convenience that results in needless environmental harm.

We need a new paradigm that turns this maximum-effort approach on its head.  Instead of collecting as much leaf volume as possible, our goal should be to encourage town residents to do as little as possible. Citizens should be encouraged to:

• leave their leaves alone, or
• rake them into an unused bit of their yard (“sheet composting”), or
• mulch them directly into their lawn.

Only as a last resort, rake them to the curb, to be trucked around by town staff and ultimately sterilized via hot composting.

The Town still has a necessary role in removing leaves from roadways and storm drains.  Getting them up off those impervious surfaces prevents rapid flow of leaf-borne nutrients into already-overburdened local waterways.  (And continued street sweeping is a legal requirement here, given that we relied on the existing street-sweeping program to comply with certain nutrient runoff reductions mandated by the Chesapeake Bay Act.)

Beyond that, the town needs to recast this annual leaf collection not as some great municipal benefit, but as a necessary evil of living in a tree-dense suburban landscape.  And as such, it should devote resources to minimizing the quantity of leaves input into this process.  I’m guessing that just a little bit of effort in this direction can both save money on leaf collection costs and generate some small improvement in the local environment.

---

Every suburbanite owns a power leaf mulcher

Let me start this section with one weird fact:  The mulching lawn mower was invented in 1990.  This, per Google Patents.  That 1990 patent document cites the the avoidance of significant monetary and environmental costs of yard waste disposal as a major advantage of a mulching mower.

Today, all mowers are mulching mowers.  Or nearly all.  My local Home Depot has 54 different power lawn mowers in stock.  I checked the first dozen listed, then spot-checked another half-dozen further down the list.  Every one was advertised as a mulching mower.  Gas, electric, multiple blade — it made no difference. To a close approximation, mulching is the default.  In the modern era, “lawn mower” is synonymous with mulching mower.  With effort, you might be able to find one that doesn’t mulch.  But you’d have to work at it.

There appears to be near-universal agreement that mulching your fall leaf litter in place is beneficial to your lawn.  By which I mean, mowing your leaf-covered lawn with a mulching mower.  Which, these days, per the above, means mowing your lawn.

Everyone from Fine Gardening to Virginia Tech Extension Service to Bob Villa says that this practice benefits your lawn.  When shredded by a mulching mower, leaf litter disappears quickly, with an upper limit of roughly half-a-foot cumulative leaf depth (per Kansas State).  The resulting mulched leaves provide a modest degree of fertilization (e.g., leaf litter is about 2 percent nitrogen). And the leaves of maple trees contain chemicals that suppress weed-seed germination (Michigan State University).

Even Scotts, the biggest vendor of lawn fertilizer in the U.S., tells you to mulch — not rake — your leaves.  (And top it off with a bit of fertilizer, of course).  The radical environmentalists at  Scotts summed up the case for leaf mulching pretty well.  (What’s next?  Exxon promoting electric cars?)

When you rake up your leaves, it costs you. Your local taxes pay for trucks to sweep up your leaves or pick up your leaf bags, all of which often end up in landfills. If you burn leaves, you're just sending up clouds of carbon into the atmosphere. Mulching leaves simply recycles a natural resource, giving you richer soil for free.

In short, if you just use a mulching mower to chop up your leaves, rather than rake them up and dispose of them, you’ll end up with a greener lawn with fewer weeds.

The upshot is that more-or-less every suburban homeowner already owns a power tool that eliminates the need to rake leaves.  That’s a radical change from three decades ago.  Once upon a time, that was a specialty piece of equipment called a mulching mower.  Now, near as I can tell, it’s called a lawn mower.  And for the few who don’t have one, the cost of on-site leaf disposal is just the cost of hiring somebody to mow your lawn with a mulching mower.

My point is that, 30 years ago, nobody owned a mulching mower.  Now, if you own a mower, it’s a mulching mower.  To a close approximation, every citizen of my town already owns a tool that allows them to dispose of their own leaves, with minimal effort, on their own property. 

So, why does my home town encourage all citizens to rake their leaves to the curb, for taxpayer-financed pickup and disposal?  Forty years ago, that was a real life-style improvement, because nobody had a convenient way to dispose of fall leaf litter.  Now, everybody does.  So why have we maintained that ancient program, unchanged?

---

Better yet, #leavetheleaves

Beyond feeding your lawn, leaf litter is reported to play a key role in the life cycle of many beneficial insects, including pollinators.  In particular, both butterflies and fireflies need winter leaf litter to survive.  You can find any number of responsible organizations who tell you not to mulch your leaves but, ideally, just let them be.  Or rake them up and let them decompose naturally.  That, in a nutshell, the worst thing  you can do is have centralized hot-composting of leaves, because that effectively eliminates next year’s butterflies, present in the leaf litter as larvae and pupae.

• Xerces Society for Invertebrate Conservation.
• Tufts University Pollinator Initiative.
• Wisconsin Pollinators.

And many others.

In particular, as this article makes clear, if you pride yourself on your butterfly-friendly garden, then rake your leaves to the curb each fall, you’re shooting yourself in the foot.  You’re basically in the business of attracting butterflies into your yard, so that you can exterminate their offspring.

While many of us are growing more sensitive to the plight of the pollinators, mindfully incorporating pollinator-friendly plants into our gardens in the spring and resisting the urge to use pesticides in our garden all summer, we are unwittingly undoing our hard work and good intentions when we clear away the leaf litter and standing dead plant material in the fall!

What?  You mean I am killing off the very pollinators that I “cultivated” all summer?  Yep.  Ouch!

Caveat:  That said, while many reputable sources say that leaving leaf litter is necessary for butterflies and other beneficial insects, I could not find even one objective study that quantified the impact of it.  So this is one of those things that you just have to take on the faith of expert testimony.   It makes sense, experts say it.  But as far as I know, it has never been quantified.

---

Nothing stops you from doing some of each

There are two types of people in this world:  Those who divide people into two types, and those who don’t.

By which I mean, thinking that you must adopt just one of the methods outlined above is arbitrary.  Nothing stops you from doing a bit of each.

This fall, maybe let some of year leaves alone.  Maybe rake some aside for your own butterfly sanctuary.  Maybe mow some into your lawn and skip the fertilizer in the spring.

All of that reduces the tonnage that the town has to collect.  And that’s unambiguously good.

---

Nutrient load in local waterways.

Source:  US Geological Survey, presented in this document.

The only significant environmental caveat that I can identify is that leaves left on impermeable areas (such as roadways) end up putting nutrients into the local waterways.  

Unfortunately, the best study of this issue (in Madison, Wisconsin) evalulated a combined program of  leaf collection (asking people to rake their leaves to the curb) and street sweeping.  You can see the full reference at this location.

That said, their conclusion is that frequent street sweeping is far more important than leaf collection, for keeping nutrients out of stormwater.  At least, that’s how I read their summary, emphasis mine:

Collection of only leaf piles, leaving streets unswept, showed no significant reduction in loads of total or dissolved phosphorus and an 83 percent increase in load of total nitrogen. The majority of nutrient concentrations were in the dissolved fraction making source control through leaf collection and street cleaning more effective at reducing the amount of dissolved nutrients in stormwater runoff than structural practices such as wet detention ponds. Based on the results of this study, municipal leaf management programs would be most effective with weekly street cleaning in areas of high street tree canopy, whereas the method and frequency of leaf pile collection is of less importance to the mitigation of nutrients in stormwater runoff.

Source:  US Geological Survey, https://pubs.er.usgs.gov/publication/sir20205109

Beyond that one study, every other reference I can find refers only to the link between tree canopy over the street, and apparent fall nutrient loading in surrounding waterways.  E.g., this one.  Similarly, this one looked at all sources, but pointed to urban trees adjacent to streets as the significant wintertime nutrient source in the watershed it studied.

So it’s pretty clear that if you have leaf-covered streets, the decomposing leaves wash into the storm sewers and add nutrients to local streams.  For sure, the town has a proper role in sweeping the streets in the fall to remove fallen leaves before they can get into the storm sewers.

But as far as I can tell, asking citizens to dispose of their own leaves, on their own property, is not a concern.  Almost all of the research shows that it’s the leaf load on the streets that is the major driver of fall nutrient runoff.  So, absent information to the contrary, I’d assume that as long as the town continues to sweep the streets in the fall, a program of encouraging residents to keep their leaves on their own lot would have no significant implications for compliance with the Chesapeake Bay Act.

---

Conclusion

Some time in the distant past, my town began a program of mass collection and composting of fall leaves.

This started before before the invention of the mulching mower.  It started decades before it was widely understood that many beneficial insects need the leaf litter to survive, and decades before research made it clear that frequent street sweeping was far more important than bulk leaf removal, for preventing high fall nutrient loads in urban storm water.

And yet, even now, every year, citizens are directed to rake their leaves to the curb, so that we can use our tax dollars to vacuum them up and send them off to be hot composted (i.e. sterilized and broken down in large, hot piles.).

All I’m suggesting is that maybe this needs a change of focus.  The town should de-emphasize centralized leaf collection and instead encourage residents to take care of their own leaves responsibly.  This can be as low-effort as simply mowing the leaf-covered lawn with a mulching mower.  It can take the form of raking the leaves to the edges of the yard to let them slowly decompose (“sheet composting”).  And then focusing the town’s resources on sweeping up whatever leaves end up on the streets.

Sure, allow residents to continue to rake their leaves to the curb for pickup if they wish.  But it’s time to stop encouraging that practice.   And, instead, to promote ways in which citizens can responsibly handle their own fall leaves.