Monday, March 8, 2010

Compost 101. Part I: The Basics

I admit that I've always been a little afraid of the idea of making my own compost. I don't know why it seemed so scary. I guess I just didn't know where or how to begin. Last year I started a compost bin in an area behind our workshop. The husband fenced off an area and I started throwing stuff in there. Leaves, carrot peelings, old potting soil, melon rinds, grass clippings, whatever. I wasn't particularly careful about how I layered it, or the moisture, or the temperature. I just let it sit there because I didn't have time to do anything with it while I worked on the house, and when I did have time, I didn't really know what to do with it!

I would have given up on the idea of making compost except that over the course of the year I realized how much stuff I was adding to the bin. And when I'd go out there a few weeks later, the pile wasn't quite as high as it was just a few weeks before. Clearly, something was happening in there, and I realized just how much stuff we generate around the house that can be composted. It seemed like a shame to send it all to the dump. So this year I've attended two classes on composting and soil preparation and I plan to be a little more proactive when it comes to my compost.

Here are a few of the basic rules for composting that I learned from my classes offered through my local extension office.

1. Make your compost bin the right size. Your compost bin needs to be a minimum of 3 feet x 3 feet x 3 feet. Bigger is better, but it shouldn't be any smaller. It needs that much total area so that the internal temperature can get high enough. That means that the fancy turning composters that you see advertised for a gazillion dollars really won't work that well because they're too small.

2. Select the right material to build your compost bin. Your compost needs enough air for the proper reactions to take place, but if you give it too much air, it will dry out too quickly. Wood pallets make excellent compost bins. Most of them are the perfect size, they're sturdy, and they have some openings in them that let in just the right amount of air. You can wire the sides together, and ideally you'll have two bins side by side. When it's time to turn the compost, you can just shovel it from one bin to the other. The bonus is that you might even be able to get these for free from stores in your area. There are a lot of plans for compost bins available online. You can start with this link and then expand your search if needed.

3. Add the right things to your compost bin. You'll need to add both "green" items that are high in nitrogen and "brown" items that are high in carbon. Green items can include vegetable and fruit scraps from your kitchen (but limit the amount of citrus peels, which don't decompose very well), grass clippings, that zucchini you didn't see in your garden until it was 3 feet long, etc. Basically, any plant material that was very recently alive will be a good source of nitrogen. Other sources of nitrogen include manures (but no cow manure; see below), hair (yours or your pet's), coffee grounds, and tea bags. Brown items high in carbon can include any plant material that's been dead for awhile, such as fallen leaves, bark or wood chips (no sawdust; see below), straw, and hay. Other sources of carbon include shredded paper (no glossy paper), and shredded newspaper or cardboard. 

To speed up the process, it's helpful to chop things up into small pieces so there is a greater surface area for the bacteria to work on.

4. Get the right ratio of carbon to nitrogen. Adjust the addition of green and brown materials to achieve a ratio of carbon to nitrogen of about 30 to 1. This ratio is important because carbon and nitrogen are the two main elements used by the bacteria in the compost pile, and the ratio will affect the rate at which they can break down the material. Here are the carbon to nitrogen ratios for some materials:

High carbon materials (C to N ratio) 
Leaves 40:1
Straw 70:1
Pine needles 80:1
Paper 200:1
Wood chips 300:1

High nitrogen materials (C to N ratio)
Fruit and vegetable waste 20:1
Grass clippings 18:1 (be careful to layer the clippings so they don't form dense clumps in the pile)
Horse manure 25:1 (with straw is 50:1)
Poultry manure 10:1

Before you start to panic about having to calculate the various ratios of your compostable materials to achieve an overall ratio of 30 to 1, you can follow a general rule of adding about half green and half brown materials to your compost pile--adding small layers of each--and then adjusting as necessary. If you have too much nitrogen, your compost pile will smell bad and be slimy. Just add more brown materials to the pile and turn it. If you have too much carbon, the pile will be too cool and you'll have a slow rate of decomposition. In this case, you can either add more green materials or just add a handful or two of a cheap nitrogen source such as ammonium sulfate, and turn the pile.

5. Monitor and maintain the temperature of your compost pile. When you put the right kind of green and brown materials together, you go from newspaper, overgrown squash, and apple cores to rich organic compost. How does that happen? One word: Bacteria. As the bacteria chow down on all the goodies you've added to the compost bin, they give off heat. If you build a good compost pile with the proper ratio of carbon to nitrogen, your compost pile should get to about 120 to 140 degrees in just a few days, and if you treat it right, you'll have finished compost in about two to three weeks.

The bacteria do their best work at around 140 degrees. If the temperature is too low a few days after you build the pile, add a few handfuls of ammonium sulfate (or some good green items) and turn the pile. It's also important that the pile doesn't get too hot or it will kill the bacteria that like cooler temperatures. The bacteria that are responsible for finishing compost prefer a much cooler climate of about 0 to 55 degrees, so turn your pile if gets to about 160 degrees so you don't kill these guys.

In addition to promoting optimal performance of the bacteria, a temperature of 140 degrees will also kill disease organisms and pests, degrade some pesticides, inactivate some preservatives, and kill most seeds.
On a related note, you may have seen items online or in your local store that you can add to your compost pile to give it a jumpstart. The instructor of my class was asked about the benefit of these and he said that if you're adding fruit and vegetable scraps from the kitchen to the pile, they have plenty of bacteria already on them, and that should be plenty to get your pile started.

So how do you know if your compost pile is the right temperature? You'll need a themometer that can reach to the center of the pile. Most of your local nurseries and garden centers will probably have them, or you can order them online, like this one I found at Gardener's Supply.

6. One other critical aspect of your compost pile is the wetness. Ideally, your compost pile should always be about as damp as a wrung-out sponge. If it's too dry, add some water and turn the pile.

7. Avoid adding some things to your compost pile. Although it seems like you can compost just about anything, there are some things that you should avoid, such as any animal products (meat, bones, fat, dairy products), dog or cat feces, cow manure, and sawdust. Although most manures are acceptable (even great) additions to the compost pile, dog or cat feces may contain harmful bacteria or diseases that are not killed by the temperature of the compost pile. Horse, llama, rabbit, goat, and other manures are really good, but cow manure should be avoided because it is usually quite high in salt and it has a very fine texture. As I'll describe in one of my next posts, it's important that the compost not be too fine or it won't do one of its main jobs when you add it to your soil. Sawdust should be avoided for the same reason.

It may sound like compost is a ridiculous amount of work, but just remember that these are the ideal conditions to create compost in the most expeditious manner. If you want to take a more lazy approach to it, you can do what I did last year. Just throw the stuff in a pile and let it do it's thing. It may take a year or two, but it will eventually break down into something you can use. You can also try the two methods I mentioned in an earlier post--trench or pit composting--if you don't want the hassle of dealing with a compost bin.

Of course, if you don't have room for a bin and you don't want to have to dig a trench or a hole in the ground, there is one other method of composting... I'll discuss it in a later post!

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