To a gardener, compost is the stuff of dreams, but to those unfamiliar this pile of dirt holds many mysteries. In this post, I will try to break down compost (heh, get it?) into the basics.


What is compost?  For the purposes of gardening, it is a mixture of decayed and broken down household and yard organic wastes. This process mimics natural cycles of decomposition found in ecosystems of all types, but most visibly on forest floors.  These natural cycles depend on the beautiful co-mingling of microorganisms, moisture, oxygen, and darkness.

When these four factors are working in harmony, they create a well-oiled compost-making machine. The biological process they facilitate is called aerobic decomposition – the decomposition of bacteria that thrive in the presence of oxygen. When the balance is off, it can lead to anaerobic decomposition, which is the slow decomposition of bacteria that thrive in conditions without oxygen. This usually leads to a slimy, smelly, disgusting pile for gross, rather than rich, dark, earthy-smelling soil.

While compost does have some nutrient benefit, especially with micronutrients, the primary benefits concern soil structure and nutrient retention. Without too much detail, the addition of compost to soil works magic in all sorts of soil, creating porosity in dense, clay soils and improving water retention in soils that are too sandy. Further, they offer to the soil COLLOIDS! These magical structures help retain nutrients in the soils. When applying nutrients in colloid-free soil, a few good soakings could leach the nutrients down below the soil horizon where veggies roots could reach. However, colloids help keep the nutrients stationary in the soil, ready to be used at will!


Farmers have used compost for thousands of years, with some of the earlier written records dating back to Ancient Rome. Back then, they would pile all agricultural waste in a large pile and let it decompose over the course of the season (which works, but is tediously slow.) Today, we have a better understanding of the components that make a good, fast and productive compost pile. There are four primary chemical ingredients for a healthy compost (not to be confused with the other four important factors mentioned above:

Carbon – for energy; the microbial oxidation of carbon produces heat (crucial to adequate breakdown and extermination of weed seeds), if included at suggested levels. High carbon materials tend to be brown and dry.

Nitrogen – to grow and reproduce more organisms to oxidize the carbon. High nitrogen materials tend to be green (or colorful, such as fruits and vegetables) and wet.

Oxygen – for oxidizing the carbon, and supporting the organisms in the decomposition process.

Water – in the right amount; the proper moisture of a good compost pile should be about that of a wrung out sponge.


Proper piles construction and maintenance for best decomposition includes a few considerations. The smaller the surface area (read size of the pieces), the faster they can be broken down.  Thanks high school chemistry for that lesson!

It’s also important to aerate the piles semi-regularly (a couple times a week) to assure that enough oxygen is getting into the pile.

While aerating, notice the moisture of the pile – if it is looking a little dry, give it some water, and if it is looking a little wet, add some brown material to soak it up a bit!

Finally, we know things are cooking away properly if the internal temperature of the pile is 135-160 degree Fahrenheit. The breakdown releases heat, so if it is too low, it’s a sign that things are not working at optimal capacity, and if it is too high, it will kill all the wonderful soil organisms.  This optimal temperature helps kills soil pathogens and weed seeds! Hurray! Of course, few people have a thermometer to stick in their pile, but if you stick your hand in it should be really warm, or, if it’s a cool morning, it should be steaming when you stir it!

But what do you put this all in? At Tom Thumb’s Student Garden we have two black plastic composting barrels that are chugging away, but you can also make a mesh pen, or heap it into a pile (recommended by biology Prof. George Ellmore.) It’s really a matter of what suits your space and preference.


Phew! That’s a lot of information! One last thing to top it all off. How much green stuff vs. how much brown stuff is ideal? Well, it seems the popular ratio is 30:1, Brown:Green. Now, each plant has different green/brown ratios, so it’s sort of complicated, but since most waste in a garden is green, the moral of the story is that you can almost always add more brown (dead leaves, newspaper, egg cartons, that test that you failed…)


Hope this was helpful! Happy Gardening!


P.S. I tried to include more soil puns, but Googling “soil puns” really doesn’t yield a lot, which surprised me with the number of garden geeks that exist in the world!