Nature Camp at the Idaho Botanical Garden is a chance for children to learn about — among many other things — compost. During a week called “Dirt Made My Lunch,” my troop of 5-year-old students and I venture up the hill to our three-bin, hot-compost demonstration area.
For many of the kids, the tops of the bins loom over their heads. They stand face-to-face with a maze of blackened banana peels, matted leaves, floppy rhubarb stalks and an army of pill bugs at work. This is the “active” pile. When I use a pitchfork to expose the center, steam billows upward, and they cluster toward the bin in awe.
As we shuffle a few steps to the next bin, I can see the children visibly deducing the sequence of events. The second bin is cold. There are few remnants of the plants and bugs present from the active pile, and it looks like dirt.
I explain that entire cities of microbacteria, highways of streaming fungi, and tunnels built by earthworms and factories of earwigs, ants and their beloved roly-polies devoured the contents of the first pile, and this is the result. The composting process is representative of how interconnected we are with creatures that are one-tenth the size of a single human cell.
Never miss a local story.
But how do you compost?
In addition to teaching, I manage the Idaho Botanical Garden’s vegetable garden and new internal composting program. Part of my job includes developing protocol for staff who will be adding or removing compost materials. IE: What should end up in the pile?
Homeowners considering this question in their own backyards will quickly learn about the concept of “greens vs. browns.” More advanced home composters will learn scientific carbon to nitrogen ratios like 30:1 and 25:1, nutrients essential to healthy compost.
However, they may not realize that the fall garden cleanup materials they are happily stacking up in their own compost piles could return to haunt them the next spring.
Many subdivisions across the Treasure Valley sit on hard, thick clay — the kind that sticks to your boots in the wet spring and is a back-breaker to dig into during the dry summer. In clay, microscopic croissant-like layers of silica-oxides make it difficult for water to deeply infiltrate the soil, and this creates water-logged areas.
It’s in this underground aquatic environment that Phytophthora spores, commonly known as root rots, can reproduce and swim freely. Many staple landscape trees and shrubs, fruit trees and vegetables are susceptible to Phytophthora. This soil-borne pathogen is suppressed by matter that includes rotting seeds and roots as well as beneficial microbes thriving in outdoor compost.
The catch is that the compost MUST reach temperatures of 131 degrees and be turned so that all parts of the decomposing material reach that temperature range. This usually happens in the first few days of material breakdown, and is the first step of the process that my students observed. Then, the compost must cure.
It all takes time
The second pile that our group of youngsters gazed up at with curious eyes is called the “curing” pile. In this stage of decomposition, acids from fresh organic material are slowly neutralized. Using compost from this pile before it’s ready can actually kill young seedlings. Curing is also particularly important for plant-disease suppression.
The extreme temperatures of active compost burn off beneficial microbes, but they will re-emerge when the material has cooled down. These tiny beneficial bioagents keep a variety of plant diseases in check.
The key here is diversity: Enclosing compost in a container (like a compost tumbler) will lower the number of microbial species that can access it, reducing their overall ability to suppress diseases. Completely suppressing plant diseases can take months of curing. A gardener can at the very least tell that the acids within the pile have been neutralized if a test seed is able to germinate in the pile.
Be careful with weeds
Another nemesis commonly lurking in compost is weed seed. It’s true that weeds can be a comparatively decent source of nitrogen. It can feel good to think that all that frustrating material is headed toward a good use.
But numerous studies have found that if the temperature of the weed seed area in the compost doesn’t reach 131 degrees, or if it isn’t isn’t properly moistened, these seeds can sprout later in your new soil.
Water expedites the breakdown of weed seed proteins in the compost at high temperatures, but too much water can reduce the heat and slow down the process. I judge my compost “well-watered” if it appears moist, but not sopping wet or waterlogged.
It’s easy to imagine a cool or dry pocket protected within a steaming jumble of materials, even if one turns and waters correctly. When it comes to weed seed, I prefer not to create a problem that I’ll have to address later. You know what gardeners say: Keep your friends close — and your enemies in a closed trash can on the curbside.
Good to go in the garden
Well-maintained compost can provide a rich reward. The last bin that our 5-year-olds visited is “ready for the garden.” Compost slowly changes the soil and plant root zone — it’s not an instant process. When mixed with soil, it can help create soil aggregates, or microscopic clumps of dirt, that provide the habitat for plant roots and beneficial bacteria and fungi.
For hot compost, turning it fully, watering it adequately and letting it cure is essential. Keeping visually diseased materials and weeds away from the pile is a choice we’ve made at the garden.
We are excited that the city of Boise Curbit program has announced a new composting system for Boise residents who aren’t able to create their own so that more “trash” gets turned into valuable compost.
People who are interested in composting at home are encouraged to visit the Idaho Botanical Garden’s vegetable garden, and learn from our three-bin system. Come visit us at 2355 Old Penitentiary Road in East Boise or visit us online at IdahoBotanicalGarden .org.
Sierra Laverty manages the Idaho Botanical Garden’s vegetable garden and is an educator at the Idaho Botanical Garden.
Be wary of adding these to your compost pile
▪ NO human, pig, dog or cat manure
▪ Fresh chicken or ruminant manure (aged is better)
▪ Meats, egg yolks, fats or dairy products
▪ Weeds (especially seed heads and rhizomatous weeds)
▪ Known or visibly diseased plant material
▪ Herbicide-treated plant material (especially systemic herbicides)
Materials that slow the process
▪ Unshredded cardboard
▪ Too much sawdust
▪ Wood chippings larger than 2 inches x 1 inch
▪ Too much wood ash
▪ Too many pine needles
Sierra Laverty’s recommended online composting resources
Backyard Composting of Yard, Garden and Food Discards by North Carolina State Extension. Great basic guide to starting and maintaining garden compost: content.ces.ncsu.edu/backyard-composting-of-yard- garden-and-food-discards
The Art and Science of Composting, by the University of Wisconsin-Madison. It’s a resource for agriculture professionals but walks the reader through the process and introductory science of composting: cias.wisc.edu/ wp-content/uploads/2008/07/artofcompost.pdf
Oregon State University has a great article on “What Not to Compost” by soil and compost scientist Dan Sullivan: extension.oregonstate.edu/gardening/what-not-compost