Steamin' Compost by Elaine Lockey

A tumbler-style compost bin

 While visiting the Rooney Road Recycling Center this winter I happened to see a rather prehistoric-looking vision.  The huge piles of brush in their organic waste area looked like primordial vents as they emitted steam on a day that wasn’t warmer than 20F. 

For gardeners, the knowledge that in the middle of a compost pile, temperatures can be over 140F - well that’s just exciting! If you haven’t already started composting, there are many resources out there to help you get started including classes and internet information.  CSU Extension has a great Fact Sheet on composting yard waste.  

The statistics are rather shocking: grass clippings, leaves and yard waste make up 20% of Denver’s household trash.  Composting yard waste combined with kitchen waste can reduce by 300lbs per person how much we send to the landfill annually. (Source: Denver Recycles) Plants lose between 50-75% of their volume in composting so it is an effective way to cleanup your yard. 

The main components to a healthy compost pile are temperature, moisture and oxygen, and nutrients.  The balance of these is critical to the pile getting hot enough and for microorganisms to effectively breakdown the waste. Microbes operate best at a range of 70-140F; temperatures exceeding 160F will kill them. Moisture is very essential to successful compost in Colorado.  You’ll need to add extra water to your pile to keep things breaking down as our natural precipitation won’t be enough to keep things going in the dryer times. It is easy to go overboard as well with moisture.  You don’t want a soggy compost pile as that will begin to smell and there will be a lack of oxygen supporting the microbes.  Your goal is moist or damp and uniformly wet.

The size of the materials you are composting is also critical.  Break apart or shred large plant pieces or other materials into ½ to 1 ½ size particles. It is not as necessary to do this with soft plant parts. Periodically turn or fork your pile to move microbes around and aerate.  Your pile also needs to be at least 3’x3’ in size to generate enough heat.  You can either fence it off or put your waste into a manufactured bin like the black tumblers available at nurseries. 

It's helpful to keep an under-sink kitchen bucket for your compost waste to easily transport to your compost bin when it gets filled.  Partially fill it with water to keep bugs and odors down.

Why are microbes hanging out in your compost pile? The plant material is a food source for them. Nitrogen is a critical nutrient for them and when that runs low they will also slow down their feeding. Green plants like kitchen waste provide Nitrogen while dry leaves and paper or straw contain little Nitrogen but do provide a Carbon source.  You’ll want a balance of equal parts green (nitrogen) and brown (carbon) waste to strike the right balance of nutrients. There are many compostable items you can use and some that you might want to avoid.

This list from Denver Recycles gives you some ideas on what you can compost and which green or brown category a material fits into. 

Browns

paper, shredded● eggshells ● sunflower stalks● end-of season annual plants ● straw

saw dust (small amounts) ● cotton string● oats● cabbage and broccoli stalks● grain hulls● tissue

cardboard cores (toilet paper & paper towels) ● wool● autumn leaves● dryer lint● lawn thatch

turnips● peanut husks● stalks from perennial plants● chipped branches● vacuum cleaner sweepings

coffee filters● corn cobs● cornstalks● cotton● landscape trimming● paper towels

Greens

alfalfa pellets● apples and peels● artichokes● asparagus stalks● bananas and peels

beans● beet tops● berries● broccoli● carrots and tops● celery● citrus fruit and rinds● coffee grounds pears● pet hair● food scraps (non meat scraps only) ● cucumbers● peas● garden waste (overgrown vegetables) ● grass clippings (no pesticides) ●moldy food (no meat, fat, cheese or bones)

● onions and skins● grapefruit● green leaves● spent hops● human hair● grapes● lettuce● manure (herbivores only) ● melons● pineapples● pond algae● potatoes and peels● pumpkins● squash

recycled water from cleaning fish tanks● weeds without mature seeds

Some waste that you might want to avoid are highly resinous wood, leaf prunings from pines, junipers, spruce and arborvitae (resin coatings prevent decomposition), plants treated with weed killers, human, cat and dog feces (disease issues), wood ash or lime.  For a more complete list visit the Extension’s Fact Sheet. 

Your compost is ready to use on your garden when it smells earthy and has the appearance of soil. You should not be able to recognize anything in it.  The amount of time to finish is highly variable but ranges from three months to a couple of years depending on the key elements above. 

Once you start composting it is hard to imagine ever throwing another apple core into the trashcan again!  It’s also a bit addictive so warn your family and friends; you might find yourself on the lookout for “compostable items” wherever you go so you can add to that pile.