Bounty from the tree canopy

This week a bewildered neighbor walking her dog saw me out raking the gutter across the street from home and asked whether I was cleaning up the neighborhood. “No,” I said, “It’s for compost. Biomass.” 

Why waste organic material?

     Oak blossoms, called catkins, had piled up on sidewalks and in the gutters. Just about every surface was sprinkled with those lacy brown chains of tiny flowers that had chosen the previous week to drop from the trees en masse. 

They're everywhere

To many, they looked like litter for the street sweeper to deal with. To me, they offered a great opportunity to add some organic material to the compost piles.

    Oaks, like many tall trees, depend on wind for pollination. That’s why they don’t bother making showy, colorful flowers and why they produce so much pollen. 

Strings of male oak flowers, like beads on a chain

The wind carries the yellow dust everywhere, to the chagrin of allergy sufferers and everyone who has to clear it from a windshield. Once their work is done, the catkins drop from the trees. I find the sheer mass of them awe-inspiring. What a vast amount of tree energy went into producing that huge volume of flowers!

     If I swept the oak catkins up and threw them into the yard waste, I’d be interrupting the soil cycle. In the forest, leaves, branches, and tree flowers fall to the ground and decompose there, becoming part of the soil that in turn nourishes the trees. 

Every part of a tree is recycled in the forest

    If those oak catkins were carted off my property to the distant industrial composting site that receives the city’s yard waste, then what my big oak tree drew from the soil to make those flowers wouldn’t be replenished. I’d be sending away nutrients and photosynthetic energy that could be here powering the garden ecosystem. 

Headed for the yard waste composting site

    Of all the compostable materials I cart to the piles in the course of the year, these oak blossoms are a favorite. They’re light and easy to gather with a rake or broom. Loading them into the wheelbarrow is a cinch. And they decompose really fast.

    Bigger pieces of plant tissue that are defended against decomposition, such as tough, leathery oak leaves, take a full two years to decompose in my compost bins. I don’t even try to compost twigs, because it would take too long. I could speed up the process by turning the piles, but I’ve got other priorities for limited gardening time. Tiny, fluffy oak catkins break down much faster, because they’ve got lots of surface area relative to their size. If I dug through the piles this fall, I’d find that soil organisms had already blended the catkins into the half-made compost.

Oak catkins break down fast into usable compost

    Another thing I appreciate about oak flowers is that they don’t come with seeds. Maples drop a bounty of organic material in spring too, those winged samaras that twirl to the ground, each carrying two seeds. I don’t compost those because so many germinate in the piles. Acorns won’t be viable until fall, so I can compost oak catkins and not worry about inadvertently planting trees.

Maple seeds-best kept out of the compost

Thanks, decomposers

With the May Day spotlight on under-valued workers, I’m grateful for the work of decomposers in the garden. Last fall I lamented my depleted compost supply. Now I’m rejoicing to see lots of fresh compost in my bins. This strengthens my impression that compost is like sourdough starter, full of what’s needed to reproduce itself. Once you’ve got the process going, it gets easier and quicker over time.

Under a layer of fall leaves in the bin, I found new compost

    That’s despite my lazy woman’s composting approach. I just pile on the garden waste as it comes. I don’t turn the piles or bother balancing the amount of “brown” high carbon and “green” high nitrogen materials. Compost still happens.

Adding fall leaves to a bin I emptied last fall

    Composting is central to my garden. With a renewed supply of compost, I’m ready to add some oomph to the perennial beds by improving soil from above—no need to dig in that extra organic material, because soil organisms will incorporate it.

Things go better with compost

    I’ll also save some compost for making homemade potting mix. By mixing it with coir, or coconut fiber, I make peat-free potting mix that works just as well as the bagged stuff I used to use for container plants.

Peat-free potting mix: because harvesting peat contributes to climate change

    In 2011, I had my compost tested for biological activity by Soil Food Web, a lab in New York. I highly recommend this experience. The lab reported the populations of the types of organisms in my compost sample: bacteria, fungi, protozoa, and nematodes. They calculated the ratio of fungal to bacterial biomass and observed that the compost was mature, bacterial-dominated, and becoming more fungal. 

     I even got a note, “One of the better compost samples I’ve seen in a while. Keep up the good work.” The only caveat: “Need to work on nematode diversity a bit more.” To that end, they recommended inoculating the pile with forest duff, the mix of half-decomposed material that lies on the forest floor. You can bet I did that right away.

Beneficial nematodes thrive on the forest floor

    Looking out at the thick layer of fall leaves I left on the beds last fall, I recognize that the whole garden depends on the same work these small organisms do in the compost pile. It’s often said that without the work of detritivores--animals such as earthworms that take in, break up, and digest dead stuff—and decomposers--bacteria and fungi that absorb nutrients from dead materials--we’d be living on top of huge piles of dead animals and plants.

    I don’t just count on these small organisms in the compost bins. They’re also hard at work building soil and turning fallen leaves into leaf mold. The wood chips that I spread on paths and around trees and shrubs last a long time, but they too are broken down, predominantly by fungi that can digest lignin, the polymer that makes wood rigid and resists rot. Without those fungi, I’d have everlasting mulch, but it would do a lot less for the underlying soil.

Wood chips would be around forever without decomposing fungi

    Composting is just a half-domesticated way of speeding up what’s happening all around us, thanks to those unseen workers.

As soil organisms break down fall leaves, they make good soil for spring flowers

Locally sourced and great

There’s a new pile of wood chips in the driveway. After a heavy wind brought down some big pine branches in the yard, arborist Kevin Newman recommended thinning the crown of our tallest pine. His team left me the resulting chips. 

I'm gradually transferring wood chips from the driveway to the garden

    Now is a great time for spreading wood chip mulch. On warmer days, I’d like to be outside doing something in the garden, but nothing’s growing. That’s when I load up the wheelbarrow with wood chips and trundle around the yard to dump them where they’re needed.

    After working with this mulch for eight years, I’m a huge fan. It’s a sustainable choice, because the chips originate in my own yard or nearby where Kevin’s men are pruning or taking down trees. The chips are easy to work with, much less dense than bark mulch. 

A wheelbarrow full of wood chips isn't too heavy to maneuver

Unlike bark, they don’t contain wax, so they don’t block water from soaking into the soil. The first time I dug into the soil under the wood chip mulch, I was amazed. It’s dark, moist and rich—just what a gardener hopes for.

    This year I’m spreading wood chips around trees and shrubs, and I plan to add some to the garden paths, where they break down fastest because of heavy foot traffic. If I do more sheet composting, they’ll be a key ingredient.

Sheet composting March 2019: wood chips on top of composted cow manure

    My source of mulch information is Linda Chalker Scott, a horticulturist and mulch scholar at Washington State University. She corrects conventional wisdom with scientific fact. For example, people worry that wood chips will acidify soil. Research shows they don’t. I’m increasingly aware that soil is not an inert substance. It’s full of biological and chemical activity, including an effective buffering system. You can’t change the pH of soil without adding chemicals such as lime to make it more alkaline or sulfur to make it more acid.

    There’s a gardening legend that high carbon mulch such as wood chips depletes nitrogen in the soil. Linda studied this and found no evidence for it. She hypothesizes that there’s a narrow band of relative nitrogen deficiency at the interface between the soil and the wood chip mulch. This is actually a plus, because it suppresses weeds. You can use this mulch anywhere in the garden except where you’re going to plant seeds or young annuals that don’t have an established root system. Like young weeds, they’d suffer in this nitrogen-poor zone.

Wood chip mulch will suppress weeds around this tree

    Can chips from diseased trees infect your yard? This is a concern I often hear from garden club members. It turns out not, because the disease organisms in mulch can’t reach plant roots. I often see impressive networks of white fungal hyphae among the chips, either in the pile or after they’ve been on the ground for a while. Linda Chalker Scott explains that these fungi are decomposers, not pathogens. With their help, wood chips decompose slowly, gradually releasing nutrients our plants’ roots can use. I’m grateful to have this free material for pampering my plants and soil.