Mulch reconsidered

 “Don’t mulch.” That was the surprising advice from native insect expert Heather Holm. What? That was a recommendation I’d never heard before. Heather’s webinar, “Attracting Bees and Beneficial Insects with Native Plants,” described the life cycles and needs of important native pollinators. Many build nests in the ground, she explained, and they need access to bare soil.

Tawny mining bee nest-photo Andrena Fulva 2d

 
    For years I’ve mulched my garden liberally. It started with an unsuccessful plan to use whole leaves to improve soil in the front yard. When they wouldn’t stay put, I invested in a leaf shredder that chopped the leaves into small pieces that didn’t blow around. Soon I was shredding all our fall leaves to spread on planting beds.

Shredded leaves make useful mulch

 
    I never had enough shredded leaves for everything I wanted to mulch, though, so I also brought in bark mulch from the garden center. In the last five years I’ve stopped using bark mulch and switched to arborist wood chips. 

     This idea came from Linda Chalker Scott, an author and urban horticulturist at the University of Washington who subjects conventional garden practices to objective scientific review. She compared different kinds of mulch head to head and found that the wood chips make superior mulch. They’re tops for holding water in the soil, modulating soil temperature, and suppressing weeds. They promote a health diverse population of soil organisms because they’re made up of a mix of different kinds of tree tissue.

 

Wood chip mulch is nice on paths and around trees and shrubs

    Wood chips fit in with my goal of reducing my garden’s carbon footprint by using locally sourced material. I get them from an arborist who works in the neighborhood.

    Now I’m re-examining my mulch approach because I want to help out native insects. What Heather advised against was bark mulch. She recommended shredded leaves, so I’m OK there. Apparently the insects don’t have a problem pushing their way through leaves to reach the soil, whereas a waxy crust of bark mulch foils them.

    Even better, Heather said, is a landscape where low-growing plants knit together on the garden floor. These plants perform the functions of mulch, and they can also provide food and shelter for native pollinators and beneficial insects (the carnivores that keep leaf-eaters in check).

 

Sweet woodruff has spread more than I'd like, but it does cover the garden floor

    Much of my garden is already provided with a groundcover layer. Two of the major players are sweet woodruff (Galium odoratum) and Canadian wild ginger (Asarum canadense). Between them they cover a lot of shady areas. There’s still not much growing under the shade of evergreens around the perimeter of the yard. This year I’m trying out native wild strawberry (Fragaria virginiana), which spreads by runners. I’m hoping it can survive and spread where other groundcovers haven’t. 

 

Wild strawberry, a native groundcover option

    Meanwhile, there are a lot more wood chips in the yard than ever before. They’ve taken the place of the lawn. Since we joined three adjoining yards to let our dogs play together, happy dogs racing around have worn away almost all the lawn grass. Instead of mud, we’re going with wood chips. I’m hoping the nesting insects will cope.

 

Lawn replaced with wood chips

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

 
   

If all you have is a hammer, everything looks like a nail

Why are landscape contractors so attached to work they can do with machines? A recent conversation with a fellow gardener reminded me of this frustration. Her lawn service uses a weed wacker—a string trimmer—to cut back weeds in her yard instead of uprooting them. 

A string trimmer shortens weeds but doesn't remove them

As I pictured it, they’re leaving the weed plants a couple of inches tall. From the weeds’ point of view, this is helpful pruning. They marshal their underground resources and send up more growth. She finds the weeds are spreading. The crew leaves her property looking neat, but they’re not serving her gardening purposes.

    I have the same experience, and it’s getting more acute as I shift toward my version of sustainable gardening. I employ a landscape contracting company that I’ve known for years. I know that the leadership of the company includes several people with strong horticultural knowledge. The actual mowing, though, is done by a team of two or three young men with many stops on their schedule for the day and little time for tailoring their approach to suit my wishes.

Can I buy lawn care that's consistent with my sustainable approach?

    Last time they visited, I happened to be out in the garden. The team leader stood next to my new perennial bed, painstakingly mulched with shredded leaves, and asked whether I wanted them to use the leaf blower. He remembered that I’d said no to leaf blowers in the past, for which I’m grateful. But I had a strong feeling that if I hadn’t been at home, my leaf mulch would have been blown off the bed in a few seconds, and I’d have been stuck buying bark mulch from the garden center.

I put that leaf mulch down on purpose

    That would have wiped out all my efforts to mulch with materials I find near home, minimize carbon cost, and maintain habitat for native insects.

    I’ve talked with the supervisor of the team at least annually about how I want to maintain the garden. I’ve put up signs asking the men not to remove fallen leaves from the property. Things have improved, but there are regular relapses. My approach just doesn’t seem to compute for them.

    Another sore spot is grass clippings. It took effort to get across the message that I don’t want them removed from my yard. That’s organic material that should stay here and build soil. I ask to let the clippings lie on the lawn. 

Instead of moving clippings to the compost bin, you can let them compost in place on the lawn-photo anneheathen

Yet each spring I’ve had to call and beg for this request to be honored. It’s not the way the team is used to doing things, and it probably looks messy to them.

    It may be more efficient for landscape contractors to do the same work in every yard and to work with power tools—gas powered mowers, leaf blowers and string trimmers--despite the dust and exhaust the operators inhale and the hearing loss they incur from the noise. But we customers are paying for this one-size-fits-all service. It’s time for us to vote with our pocketbooks and seek out contractors who are equipped to accommodate a more plant-friendly and environmentally conscious approach.

Pushing up through the leaf mulch

 

Wake up and smell the leaf mulch

Last fall I changed a longstanding fall garden clean-up routine: I didn’t rake fallen leaves from the garden beds and chop them up in the leaf shredder. I didn’t mulch those same beds with the chopped leaves. I didn’t cut the dead perennials’ foliage and flower stalks to the ground. I just let the tree leaves lie on top of the plants and left the dead stalks standing.

Meadow rue (Thalictrum aquilegiifolium) emerging through the leaf litter

    My reason for this change of approach was that I’d learned that native insects shelter and lay eggs under fallen leaves, in crowns of dormant perennials, and in those dead flower stalks. If I left those insects alone through the winter, they’d have a better chance of surviving, reproducing, and contributing to the garden ecosystem in spring. It was hard to hold myself back from cleaning up at the end of the garden season. I have to admit it was also a lot less work.

Beneficial lacewing finding winter cover

    Through the winter, I watched those ragged stalks and those whole leaves, especially on the new perennial bed that’s right next to the back deck. The leaves are mostly red oak, with some Norway maple mixed in. The garden’s usual winter look, bare but neatly tended, had morphed into either a sloppy mess or a more natural scene, depending how I felt on a given day. 

The backyard scene in March

Now is the time to assess how this lazy approach to preparing for winter worked out.

    I waited impatiently for daytime temperatures to stay in the fifties, indicating that the time had come for lifting the leaves off the new plants and moving them to the compost pile. I was anxious to know how the plants were doing under there. For the past two weeks I’ve been gradually uncovering the deck bed. 

Perennials and a dwarf juniper under the leaves

Dry leaves formed the top layer, but beneath these I uncovered wet, matted leaves plastered to the ground. I chose overcast days with rain in the forecast, not hard to find recently, for exposing the covered plants to the light. Their new foliage was pale from growing in the dark. I didn’t want them to get sunburned from sudden exposure to full sun.

    With the whole bed uncovered, I see that most of the new perennials made it through the winter. Of course, they benefited from other factors besides the leaf cover. Snow covered the bed during much of the winter, protecting the new plants from desiccation and temperature extremes, and there’s been plenty of rain this spring.

    To mulch the uncovered bed, I shredded leaves that I’d stored in the garage in paper yard waste bags. 

Shredding makes mulch that doesn't mat or blow around like the whole leaves

If insects took refuge in the bags last fall, they should have moved out by now. Birds are very active in the yard, which seems like an indication that they’re finding insects to eat. 

A cardinal couple is building a nest

     I’m hoping that more native insects will enrich the garden’s food web this year. Not only animals will benefit. I’m aiming for plant-friendly balanced populations of pollinators, leaf-eaters, and the beneficial insect predators that will keep leaf-eaters under control.

Leaf litter and native insects make congenial conditions for woodland plants