When it’s time to say goodbye to your Christmas tree, where will it go?
“Live trees picked up from residential neighborhoods will be treated the same way as yard waste,” said Spencer Campbell, Plant Clinic manager at The Morton Arboretum in Lisle. “They will be ground up and processed for use as mulch and compost.”
Landscape waste, including Christmas trees as well as grass clippings and autumn leaves, has been banned from landfills in Illinois by state law since 1990. In addition to reducing the volume of waste stored in landfills, the ban minimizes the release of methane, a potent greenhouse gas that contributes far more to climate change than carbon dioxide.
Methane is produced when organic matter, including food, yard waste and wood, rots in oxygen-poor conditions, such as when it is buried in a landfill.
State law requires landscape waste to be either composted in your yard or reprocessed into mulch and compost in large, industrial-scale facilities. “Compost or mulch will still decay over time, but much more slowly,” Campbell said. “In the meantime, it will improve the soil and release nutrients to benefit plants.”
Because there is plenty of oxygen available outside a landfill, the decay process is different and it releases far more carbon dioxide than methane. Although carbon dioxide gas also traps heat in the atmosphere and contributes to climate change, it traps heat far less efficiently than methane because it has a different chemical structure.
Organic materials, including food waste and landscape waste, account for about 30 percent of the waste stream in Illinois. “Keeping that quantity out of landfills is a big economic and environmental benefit, and it also helps our trees and plants,” Campbell said.
When Christmas trees are collected for disposal, the first step is to put them through a wood chipper—the same machine that is used to grind up branches from tree pruning. Such machines can be set to grind larger or smaller pieces. Coarsely ground wood, with big pieces that will decay relatively slowly, usually ends up as mulch. A finer grind may be used for composting, because smaller pieces have a larger surface area for their size and will be broken down faster.
“Commercial composting is based on the same principles as your home compost pile,” Campbell said. “It creates conditions that invite bacteria and other soil organisms to partly consume organic matter so it’s easy to use as a soil amendment.”
At home, you can accelerate the process by keeping your compost pile or bin moist and turning the materials over every few weeks to mix them up and allow more oxygen to reach the composting organisms. “It encourages them to multiply and chow down,” Campbell said. To learn more about home composting, see mortonarb.org/composting.
Commercial facilities turn their compost far more often. The ground-up organic matter is usually heaped in long, straight piles called windrows that are turned with excavation equipment or with special machines that roll along a windrow while continuously turning and watering the organic materials. The windrows are monitored to make sure the composting bacteria and other organisms have just the right amount of oxygen and moisture to reproduce readily and stay active throughout the large mass of organic matter.
Heat is a byproduct of all this bacterial activity, so commercial compost gets much hotter than most home compost piles ever could. The heat can kill off disease organisms and weed seeds that might survive in home compost. “It’s best for weeds with seeds and any leaves or branches that show signs of disease to go into the landscape waste and on into the commercial compost stream,” Campbell said.
In the propitious conditions of a moist, oxygen-filled, frequently turned windrow, it takes just a few weeks for wood and other organic waste to break down into fluffy, nutritious compost. In the cold of winter, the process may be slower, but it still goes on.
The resulting compost may be sold to landscape contractors or packaged and distributed for sale in garden centers. It also is used as an ingredient in potting mixes.
To make sure your Christmas tree runs through this process smoothly, carefully remove all decorations and plastic tree bags when you set it out for pickup. “Plastic or metal left on trees can jam wood chippers, and they can’t be digested by bacteria,” Campbell said.
Since each municipality has its own rules and schedule for tree disposal, ask local officials or consult your town’s website to find out exactly where and when to set out your tree. For more tips on Christmas tree disposal, see mortonarb.org/tree-disposal.
For tree and plant advice, see the online resources of The Morton Arboretum at mortonarb.org/plant-care, or submit your questions online at mortonarb.org/plant-clinic or by email to plantclinic@mortonarb.org. Beth Botts is a staff writer at the Arboretum.
