This week the world’s gardeners will talk about dirt. Or more specifically, compost.

It’s International Compost Awareness Week. To mark the occasion, some local experts offered tips on composting in the desert.

But first, some basics.

Compost is organic matter that has broken down to become a soil amendment. It’s not dirt, but helps dirt become a thriving ecosystem of microbes and other creatures.

Composting increases the number of beneficial bacteria, protozoa, nematodes, arthropods, worms and insects by giving them something to eat. Their presence in soil adds nutrients, retains water and reduces the acidity of desert soil.

“To be an effective composter, you need to think of the compost pile as both a food source and a habitat for this amazing menagerie of munchers,” says Parker Filer, assistant agent of horticulture for the Pima County Cooperative Extension.

Compost recycles plant-based waste. It starts with combining carbon-rich material such as straw, small branches, leaves and grass clippings with nitrogen-rich items such as food scraps, coffee grounds and animal manure.

They’re mixed with some water, oxygen and native soil, which adds the microbes that start eating and multiplying. The result is dark, crumbly dirt.

WAYS TO COMPOST

There are many ways to compost. Here are what local composters do.

Cold composting: These methods don’t depend on heat to break down material. They’re fairly simple operations, but could take a long time to create compost.

“A really simple way to dispose of kitchen scraps is just toss them out in the garden beds,” says Elissa Dearing, program coordinator for the Green Valley Gardeners’ Desert Meadows Park Community Garden.

Another method is vermiculture, which relies on worms to eat food scraps and then poop nutrient-rich castings into soil.

Filer says a covered bucket can be kept indoors to do this. Another option is to create a tower in which worms dig through soil to eat scraps.

The Green Valley Gardeners uses a 5-gallon bucket into which holes are drilled. It’s buried into a garden bed nearly up to its opening and filled with leaf litter, veggie scraps, shredded paper and worms. The critters go in and out of the bucket buffet through the holes, adding their castings directly into the bed.

Tip: Filer suggests not feeding worms citrus, which can make the bin too acidic for them, or meat and dairy, “which will give the worms indigestion.”

Hot composting: Heat speeds the composting process and kills off microbes that can cause disease and weed seeds.

Most hot composting methods require constant watering of the pile and regular turning over to aerate it. Tumblers with cranks make turning easy and take up little space.

Open bins easily provide needed air and can compost large amounts of debris and scraps. Two or more bins can keep a composting operation continuously going. One bin could have compost ready to shovel into beds while the other is processing, or cooking, the material.

A keyhole garden at the cooperative extension demonstrates a more direct hot composting system.

Master gardeners built a raised bed shaped like a keyhole with access to a mesh-lined hole in the middle of the bed. Material to compost goes into the hole.

Watering and some mixing get the material hot, says master gardener Cathy Hoyt. Watering the compost irrigates the plants while pushing nutrients into the surrounding soil.

“These things are supposed to work in climates like ours,” says Hoyt. They were developed for African farmers in hot, dry climates.

The key is to maintain the compost pile. “People need to be dedicated,” she says, “It’s not a plant-it-and-leave-it sort of thing.”

Other tips for hot composting:

  • Chop up material. The smaller the pieces, the more surface area is exposed, which speeds the process.
  • Successful hot composting has a good balance of material, stays as moist as a wrung-out sponge and maintains an internal temperature of 120 to 170 degrees, says compost educator and landscape designer Jason Isenberg.

For extreme composting, consider a composting toilet.

Watershed Management Group sells a two- and a three-barrel outdoor system to collect human feces and urine.

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One 50-gallon barrel is topped with a toilet seat to collect human waste, toilet paper and added carbon.

Once it’s full, it’s covered to allow the material to cook, says Catlow Shipek, the nonprofit organization’s policy and technical director.

The toilet seat is moved to the second[second] barrel to collect a new batch.

Human manure provides the microbes, water and nitrogen for composting, Shipek says. It gets hotter than compost using solely plant waste.

The resulting product is safe as soil amendment in a home garden, although it should not have direct contact with edibles.

Use of composting toilets “is still very much fringe,” Shipek admits, “but I think it’s a growing fringe. There definitely is an uptick in interest.”

RESOURCES

Several experts say the best system to compost is one you’ll use. To that end, here are some resources to decide what might work for you.

  • Tucson Botanical Gardens, 2150 N. Alvernon Way, has an exhibit that shows various compost tumblers and bins.
  • The master gardeners’ keyhole garden is available for public inspection at the cooperative extension demonstration gardens, 4210 N. Campbell Ave.
  • Two types of composting toilets are on display at Watershed Management Group’s public Living Lab, 1137 N. Dodge Blvd. Information is available at watershedmg.org.
  • Tucson Organic Gardeners has information on composting at tucsonorganicgardeners.org/publications.
  • Pima County Cooperative Extension has several publications on composting. See a list at extension.arizona.edu/composting-resources.
  • Classes, talks and workshops are scheduled throughout the year by the botanical gardens, master gardeners, Tucson Organic Gardeners and the Community Food Bank of Southern Arizona.

Emily Rockey, director of sales and marketing for Tank’s Green Stuff, believes that composting requires careful monitoring and good practices. “If all ... things don’t come together, you’re not going to have success,” she says.

Others don’t agree.

“The big thing I tell people is don’t worry about it so much,” says Dearing of Green Valley Gardeners. “If you just throw stuff in there, it’s going to eventually break down.”

Jim Lootens, a specially trained master composter and Tucson Organic Gardeners member, echoes that feeling: “Whatever you get is better than what you started with.”

Contact Tucson freelance writer Elena Acoba at acoba@dakotacom.net.