Leave the leaves

What used to be a far-out, novel idea is now joining the mainstream: “Leave the leaves.” To support biodiversity and especially to provide protection for native insects, gardeners are changing our fall routine. For the past three years, I’ve been letting whole leaves lie on my garden beds.  

 

Whole leaves work as mulch

    This change allows me to do a lot less work. I used to spend many hours in late October and early November raking leaves to a spot at the back of the house where I could plug in my leaf shredder. I’d feed as many leaves as possible into the machine--basically a string trimmer in a drum—to make shredded leaf mulch for my perennials. 

 

Leaf shredder: effective but labor intensive

Now I just gather leaves from the driveway, the sidewalk, and the roadway along our block, rake them onto a tarp, and drag the tarp into the backyard. There I dump the leaves on whatever bed seems to need a blanket of mulch. 

    The concept behind this time-saving approach is that lots of native insects overwinter in fallen leaves, whether as eggs, larvae, nymphs, or adult insects. When I chop up leaves in the shredder, I’m chopping up those insects, reducing next year’s population of native insects in my yard. That’s working against myself, because I need a balanced population of leaf eaters, pollinators, and beneficial insects—the predators that keep leaf eaters in check—to keep my garden ecosystem healthy.

 

I want to host beneficials like this lacewing

 
    While environmentalists and proponents of sustainable gardening advocate for leaving the leaves, I’m disappointed to notice that some of my favorite garden writers are pushing back. I’ve read warnings that a cold-season mat of whole leaves will damage turf grass. Yes, we all knew that! Another worry is that perennials won’t thrive under a blanket of leaves. The thought is that plants from Mediterranean climates may need breathing room and a drier environment.

    All I can say is that these commentators must be gardening very differently than I do. Most of what used to be turf grass in our yard is now covered with wood chips that have no trouble accommodating a layer of fall leaves. And my perennials are ones that have proven tough enough to survive the conditions in the yard—sandy soil, rabbits, varying degrees of shade, humid summers with periods of drought and, increasingly, cold snaps in winter without snow cover for protection. If perennials needed pampering, they’ve long since died out in my garden.

 

Lavender toughs it out in the garden without special treatment

 
    Given my limited perennial-growing ambitions, I’ve had no trouble with leaving the leaves. Increasing numbers of birds visiting the yard suggest we’ve got more native insects than we used to.

    In spring I do like to peel back the matted leaves from the newest perennial bed off the back deck. It’s quick work to dump them in the wheelbarrow and move them to the compost piles. If I’ve got some dry fall leaves in bags in the garage, I’ll shred them at that time to replace the mulch I’m taking away. Moderation in all things.

Dwarf crested iris, another survivor

 
 

A fair exchange

An excellent summary by Anne Bikle in Fine Gardening reminded me that there’s no free lunch in the rhizosphere, the top few inches of soil where most of the biological activity happens. True, lots of soil organisms are at work breaking down organic matter into forms that our plants’ roots can use. 

Electron micrograph of soil microbes-photo Pacific Northwest National Lab

But that’s not a coincidence. The roots offer something in return. Every plant exudes proteins, carbohydrates and fats from its roots. These attract the organisms that help plants get what they need and protect them from diseases and pests.

 

Fungal network associated with spruce roots-photo André-Ph. D. Picard

 
    Bikle’s article was a good reminder to support this process by taking good care of soil organisms in the garden. I checked myself against her three recommendations: leaving soil undisturbed when possible, mulching to add organic material to the system, and growing a variety of plants.

    A few years ago I gave up turning the soil in the vegetable bed with my spade before planting in spring. I’d thought this was a necessary step to mix in amendments such as compost and composted manure and turn under any weeds that had sprouted.

     I stopped all this digging when I learned it was counterproductive. I was breaking up soil networks, killing or slowing down soil organisms that were nourishing my plants. I was also churning through organic material by introducing a rush of oxygen into the soil, wasting the compost I added to the bed. 

     I found out it was better to let soil organisms do their work undisturbed. Now I confine the digging to times when I need a planting hole for a seedling such as a young tomato plant. The soil in the vegetable bed has improved. As a side benefit, I’ve got fewer weeds, because when I cut out the digging, I stopped bringing weed seeds to the surface to germinate.

I avoid digging except to plant seedlings

    I’m also making a point of not clearing away leaves that fall on the ground, except on the lawn. I’m still working on striking a balance for fall leaves. I used to chop them up for leaf mulch, until I learned this also chopped up useful insects at various stages of development that were settling into the leaf litter for the winter. For the past couple of years, I’ve mostly let the leaves lie on beds, supplemented by more leaves I drag in from the street that would otherwise go to the city’s composting site. 

 

Letting fall leaves lie

     

     Now I’m missing my leaf shreds. There are places where they’d be especially useful, such as in the newest perennial beds, where the soil could use some quick help. The leaf shreds stay put, not blowing around like whole leaves, and they decompose faster. This fall I think I’ll do some limited shredding to cover those spots.

 
     From Bikle I learned that I’m offering a diverse buffet of root exudates by increasing variety in the garden as I’ve added native plants. That’s because each plant sends out its own recipe to attract organisms to meet its needs. All the better.

 

A mix of native plants: wild ginger, leucothoe, heuchera

 

Compost shortage

Once my composting operation settled into a routine, I could count on having two of my four bins produce a good supply of fully made compost every year. Every fall I spread a thick layer on the vegetable bed, where organic matter is used up fast by food-producing annual plants. 

Food compost from the closed bin will enrich the soil of the vegetable bed

When I planted new areas, I spread compost on the soil surface before starting to dig. When I learned that harvesting (really mining) peat contributes to global warming by releasing carbon, I started mixing finished compost from the bins with coir (coconut fiber) to make homemade peat-free potting mix.

     This year I haven't produced as much compost as I used to, and I'm going through it faster. Last year I gave away so many potting mix samples that I ran short of finished compost. 

Cute, right?

The reason for the samples was to interest garden club members I met in making their own peat-free mix. I thought if they tried mine, they'd see how easy it is to make a mix that looks, feels and functions a lot like commercial products based on peat. 

     Last year too I piled fewer fall leaves into the bins. I used to heap up leaves on the bins at the end of the gardening season, knowing the fluffy mounds would flatten during the winter, gradually decompose, and become part of the compost. But last year I went big on piling the whole leaves on beds to provide winter shelter for native insects.

Collecting leaves from the sidewalk to pile on garden beds

     Another call on my compost supply last year was the sheet composting project I started last March. The majority of the material for this composting-in-place soil improvement mound came from thick layers of wood chips and fall leaves. Thinner layers of compost were needed, though, to introduce soil organisms that would do the decomposing. I can see that they're doing their work. Already this fall the mound has sunk to about half its original height.

The sheet composting mound is sinking and starting to look like soil

     These extra demands on my compost economy have left the bins nearly exhausted this fall. Cutting down vegetable plants and emptying summer containers, I've started the process again in two of the four bins. According to the old system, though, the other two bins should be full of year-old developing compost. They're not.

The cupboard is bare

     In the past, I've just waited two years for the compost to be finished. Usually I make a point of adding garden waste to the compost as it comes, with no recipe. But I don't want to go through next summer with no finished compost. I may have to adjust my lazy-woman's composting method this year. 

     To get back on track, I can mix shredded leaves with the dead plants in the bins. 

Shredded leaves will decompose faster

Combining "brown" high carbon and "green" high nitrogen components will speed up the process. Desperate times call for desperate measures.

New aesthetic needed

With October gone, the leaf blower season in my area is officially under way. Rain and heavy winds have brought down a lot of leaves, and many homeowners feel those leaves need to be disposed of post-haste. That means blowing or raking every last leaf into a pile and stuffing it into a leaf bag or vacuuming it into a truck to be transported to “away,” wherever that is.

Move 'em up and move 'em out

    Two years ago some local citizens rose up to protest the noise and health risks caused by leaf blowers. Some towns around the country have imposed meaningful limits, and some have even succeeded in passing outright leaf blower bans. But here, the team I was backing lost the fight, or at least the first round. We ended up with a complicated new noise ordinance that still allows leaf blowers seven days per week, with gas models permitted before Memorial Day and after Labor Day. 

After Labor Day, gas-powered leafblowers are free to roar in my neighborhood

I think this means the anti-leaf blower faction underestimated the determination of local landscape contractors to defend their business model. Leaf blower noise continues at a cost to the rest of us: loss of quiet enjoyment of our property. I hope we’ll eventually achieve an ordinance with more teeth.

    If I ran the zoo, we wouldn’t need leaf blowers because we wouldn’t clear fallen leaves from our yards. My town, like many, is stuck with a standard of landscape maintenance that dates to the aftermath of World War II. According to this aesthetic, fallen leaves are whisked out of sight as quickly as possible, and an ideal front yard consists of a swath of neatly mown lawn, as big as possible, backed by a few shrubs planted against the house’s foundation.

Neatness reigns

    As I’ve traveled farther along the path to a sustainable garden, I’ve gotten increasingly comfortable with seeing leaves on the ground. Fallen leaves on garden beds used to look like a mess to me. Now they’re a pleasing part of the view, just the way they’d be on a walk in the woods.

Fallen leaves enhance the beauty of the woods

    I’ve learned there are lots of good reasons to let those leaves lie on the ground. They add organic material to the soil as they slowly decompose, providing nutrients for plants and improving soil structure. They offer shelter for native insects, helping them survive the winter. They act as mulch, minimizing the number of weeds I’ll be coping with the next spring, insulating the soil so a sudden thaw or cold snap doesn’t kill my plants, and helping to hold moisture in the soil for roots to access.

Fallen leaves and pine needles benefit this shady bed

    Now I wonder why my neighbors bother to send away all that valuable organic material and then pay to replace it with mulch or soil amendments. If we send those leaves away, we’re actually depleting our own soil, because what our trees drew from the soil isn’t replenished by decomposing leaves.

Why send away organic material that should become part of your soil?

    But the truth is, I wouldn’t be letting those leaves lie if I hadn’t come to find them pretty. In garden design, neater isn’t always better.

Lots to love about leaf mulch

The word is out: leaf mulch is great. 

Shredded leaves make high-quality, free mulch

   I’ve been chopping up fall leaves for mulch since sometime in the 1990s. These days I mulch most beds with whole leaves, because they provide shelter for over-wintering insects. I still use chopped leaves for areas near the lawn, because they don't blow around. 

     Many people chop leaves with the lawnmower. I prefer to use a standing leaf shredder, essentially a string trimmer in a drum. Plastic filaments whirl around and chop the leaves into small shreds. The resulting mulch is pretty, it doesn’t blow around like whole leaves left on the ground would, and it’s great for building soil fertility. And the electric-powered shredder doesn’t generate exhaust.

Electric leaf-shredder doesn't pollute the air

    The Rose Kennedy Greenway, the linear Boston park created in 2008 when the Big Dig moved the highway underground, uses organic methods and has recently experimented with switching from bark mulch to shredded leaves. The product they apply, which you can now buy from landscapers, has a step added to my process. After the leaves are chopped, they’re composted for a year. Horticulturists for the Greenway find the composted leaf mulch is full of beneficial soil organisms.

Rose Kennedy Greenway-photo Tim Grafft/MOTT

    As their test area, the Greenway chose a section of the garden devoted to New England native plants. After three years, they’ve found substantial benefits. In the leaf mulch beds they’ve measure increases in soil organic matter. They’ve also found increased cation exchange capacity, which allows soil to hold on to nutrients and buffers it against excess acidity. In fact, the soil in these beds has improved so much that Greenway staff have to consider whether the soil may become too rich for their native plants.

    One of the few drawbacks of leaf mulch at the Greenway has been small fires in the mulch from discarded cigarettes, which apparently isn’t a problem with bark mulch. Let’s hope visiting smokers can learn not to throw cigarette butts into the garden!

It counts as littering

    The City of Newton passed on a recommendation from Michigan State University for mulching lawns with chopped leaves. Lawn lovers hate the idea of letting leaves lie on lawns through the winter, where snow piled on matted leaves can kill the grass. That’s is one of the reasons for our suburban cultural taboo against letting fall leaves lie.

No fall leaves allowed on the lawn

    Instead of doing all that work raking and bagging the leaves, though, MSU turfgrass scientists found they could save time and improve lawns by chopping the leaves on the lawn with a few passes of a lawn mower. The little leaf fractions sift down out of sight among the turf plants, providing a mulching function that suppresses dandelions and crabgrass by up to 100 percent after three years. The decomposing leaf shreds also fertilize the lawn.
 

Chopping leaves with a lawnmower-photo Rebecca Finneran, MSUE

    My focus when I chop up fall leaves has been on improving the soil for shrubs, vegetables and perennials. The lawn is on its own. But after hearing the MSU results, I think I’ll set up my leaf shredder on the lawn this fall to spread some of those leaf bits around while I make mulch for the beds.

Perennials could share some leaf mulch with the lawn

    I’ll be demonstrating the leaf shredder in action at a hands-on sustainable gardening course in my yard Saturdays October 26 and November 2. You can sign up here through Newton Community Education.

Leaving the leaves

Last fall I departed from past practices and let fallen leaves lie on all my garden beds through the winter. The reason for the change was a new recognition that this would help native insects make it through to spring. As the weather warms and daytime temperatures stay moderate, I’m having the first opportunity to assess how this worked out.

Bloodroot emerging from last fall's leaves

    Years ago, I tried using whole leaves as mulch to improve soil in the front yard. I soon recognized that this was an un-neighborly act, because the leaves blew off our property and ended up on other people’s carefully raked lawns. This blunder led to the purchase of a leaf shredder. Shredded leaves stay put. I used them as mulch for about 20 years. 

Shredded leaves make nice mulch and don't blow around

    Then I learned that by chopping up the leaves, I was probably also chopping up desirable insects. Some dormant adult insects spend the winter hiding among the leaves, and others lay their eggs there. If I let the whole leaves lie through the winter, the eggs could hatch and adult insects could emerge when the weather warms in spring. 

Beneficial lacewings can winter in leaf litter

Those emerging insects would contribute to a healthy balance of insect populations in the garden. That’s why last year I not only let leaves that fell on the backyard beds lie un-shredded. I also dragged in as many leaves as possible from my block and a neighbor’s lawn. All those brown leaves are now lying on my garden.

    I’m still working out this system. My approach this spring is to rake the top layer of fall leaves gently off perennial beds. New shoots from the perennials don’t seem to be able to reach the sunlight through mats of undecomposed whole leaves. I see new growth heaving up a section of leaf mulch, and I can’t resist lifting the leaves off to uncover the emerging yellow-green stalks. 

I peeled away the top layer of leaves to uncover emerging perennials

This may be a remnant of an old way of thinking. Maybe next year I’ll have learned that even this careful raking isn’t necessary.

    Around trees and shrub, though, the whole leaves seem to be doing nothing but good. Like wood chips, they’re keeping the soil steadily cool and moist. They seem to be suppressing weeds too, like any good mulch. 

No need to rake away fall leaves that surround trees and shrubs

Tough, leathery leaves from our neighborhood’s red oaks decompose slowly. Even so, they’ll eventually break down and add organic matter to the soil. Like my sheet mulching project, this is essentially a way to let compost happen with less intervention. Instead of moving leaves to the compost pile and then carting them back to the beds after they decompose, I’m letting soil organisms do the work where the leaves fall. Imitating natural processes is a lot less work!

    I do need to move some of those leaves to the compost piles, though, because the bins are pretty depleted. I’ll need some compost to make homemade potting mix. No worries—there are plenty of leaves to spare.

Leaves will help make compost for peat-free potting mix

 
   

Before the freeze

Come visit my table at Celebrate Newton, a holiday craft fair, on Sunday December 2 from 10 to 4.


Despite interruption by early snow, I’ve spent the past week hurrying to prepare the garden for winter. A list of chores always looms as the light for working outdoors shortens and the ground gets ready to freeze.

Snow already! Time to rush through the last garden tasks

    Number one on the list is gathering in as many fallen leaves as possible and spreading them around the garden. This fall I’ve reverted to shredding leaves to mulch the new perennial beds at the back of the house. I’ve been shredding less since learning that whole leaves shelter insects and other animals through the winter. 

Letting whole leaves lie for shelter

Last spring I found I had to peel back layers of whole leaves I’d piled on these new beds to uncover the emerging young perennials below. That would have been OK, but once those leaves were gone, there was no mulch left on the bare soil between plants. The thin layer of bark mulch I'd applied when I planted the new perennials had long since decomposed. Until the plants grow to full size, I think they'll need some shredded leaf mulch.

     Everywhere else in the yard, I’m piling up whole leaves. My neighbor Pat kindly donated her bags of raked leaves. I go out periodically and collect leaves from nearby sidewalks and gutters, piling them on a tarp to drag into the backyard. 

Precious cargo

At this point, the drifts of fluffy leaves look way too deep, but I know they’ll settle to a reasonable layer of a few inches as the winter comes on.

    I’d hoped to use potting mix from the large pots that hold my container plantings to layer on top of the grass where I’m planning to enlarge a bed. Cold weather came too soon, though. Starting that new planting area with layers of cardboard, wood chips and compost will have to wait until late winter, when some tree pruning should provide me with a big pile of wood chips. 
  
    Frost reminded me to move hoses and watering cans into the garage or basement. 

Time to put away the hoses

The last job of all will be to wash the large ceramic and plastic pots and move them indoors. Freezing and thawing outdoors through the winter shortens the lives of pots and hoses. I eventually store all the pots in the basement but never get around to washing them until the garden is completely dormant.

I'll wash ceramic pots and store them in the basement--eventually

    A few end-of-fall tasks prepare for indoor gardening. I sifted finished compost from one of my piles, transferred it to a bucket, and ferried it into a large plastic garbage bin in the basement. There it’s available to mix with coir—coconut fiber--for making homemade potting mix. I’ll use that to proselytize for moving beyond peat-based potting mix, giving out little sample bags when I visit garden clubs.

    Saturday I picked out amaryllis bulbs at the garden center. With compost and coir in the basement, I’m ready to pot those bulbs in peat-free potting mix. We’ll enjoy their giant flowers in the warm kitchen while winter rages outside.

Amaryllis flowers light up the dark months-photo pizzodisevo

Helping more by doing less

The Xerces Society, which works to protect invertebrates and their habitats, has created nine handsome posters to advocate letting fall leaves lie. They’re offering them in printable form on their website to spread the word that leaves on the ground are necessary for moths, butterflies, bumblebees, and many other garden contributors.

    The reason to let leaves lie on the ground through the winter is that so many species use that leaf layer for shelter. Most butterfly and moth species don’t migrate. They need to make it through the cold months in some stage of their life cycle, whether it be as an egg, a chrysalis, or an adult. Bumblebees don’t gather in hives, and they too welcome an insulating cover of leaves over the shallow holes in the soil where their queens spend the winter.

Fertilized bumblebee queens survive the winter in holes in the ground

    I’m working to welcome these insects and many others to my garden: leaf-eaters, pollinators, and the beneficial insects that, as predators, keep bug populations in balance. 

Dragonflies are top predators, useful for keeping leaf-eating insects in check

I’m counting on these native insects at the base of the food web to keep my plants healthy and my garden a welcoming place for birds and other animals. The three pillars of this approach are avoiding pesticides, choosing the right plants, and letting those fall leaves lie on the ground.

It might look messy, but letting leaves lie is more sustainable

    To help out native insects, I’ve completely discontinued pesticide spraying, even for nonnative pests without local predators. That’s to avoid killing off native insects with friendly fire. No insecticide is so targeted that it doesn’t cause unintended casualties.

In the woods, leaf litter is free of pesticides and stays undisturbed on the ground.

    I’m also choosing plants with the insects in mind. Last week students at a hands-on Newton Community Education course in the yard helped plant my latest insect-attracting shrub, a New Jersey tea (Ceanothus americanus), adding more native flowers to offer pollen and nectar in spring. 

New Jersey tea flowers offer premium pollen and nectar

This little shrub will grow into a 3-foot mound and attract butterflies and hummingbirds to its white or pale lavender flowers. 

     I’m looking forward to experiencing New Jersey tea’s spring fragrance. It’s drought tolerant once established, which fits with my efforts to water less. Right now it’s leafless, showing a few of the yellow twigs that will stand out in the winter landscape when it settles in. When next year’s leaves fall to the ground, they'll help insects through the winter.

    I could undo some of the benefits of planting insect-friendly perennials and shrubs by bagging up my tree leaves and setting them out at the curb for yard waste pick-up. 

Insects lose winter habitat when organic material goes out as yard waste-photo Bill Barber

The Xerces Society warns that sending away those fall leaves--or chopping them up with a lawnmower or leaf shredder for mulch—would be discarding or destroying insects and their eggs and larvae already sheltering among the leaves.

    Not shredding leaves for mulch will save a lot of time and energy. I can spend some of that time piling leaves around trees and shrubs that could use some extra insulation. And there’ll be time to cook up lots of schemes for moving plants around next spring. That’s the beauty of a garden. It’s never finished.