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As usual, I start out talking about compost and think I can finish it all in one column, but I never do. However, this third week in a row is the last time I will discuss compost this year. I promise.

So, after all the dos and don’ts of the last two weeks, here is the final recipe: You need carbon and nitrogen, at about a 30-to-1 ratio. In other words, for every 30 parts of carbon, you want 1 part nitrogen (to be truthful, as low as 25 parts carbon to 1 part nitrogen will work almost as well).

Just to give you a rough idea, a compost pile that is half brown leaves and half grass — by weight, not volume — is around 30 to 1. The general rule is that if it is green it has a lot of nitrogen, and if it is brown it has a lot of carbon. There are exceptions, with the most common being evergreen needles and manure. Evergreen needles keep green all year because of a waxy cover, but they are not high in nitrogen despite the color. And manure is brown in color but is high in nitrogen and thus a green.

Browns, that is carbons, provide the energy for metabolism. Greens, the nitrogens, feed the bacteria.

You need two other things in addition to greens and browns: air and water. Turning the pile (or using the PVC pipe method) provides the air, but don’t depend on the rain to provide sufficient water. Your pile should be about as moist as a sponge with the water squeezed out, and in Fairbanks this will require the assistance of a hose. If you make the top of your heap a bowl, that will catch what available rainwater there is and thus reduce some of your watering chore.

If your pile is too dry, the metabolic activity will stop and your pile will just sit there. When this happens, add more greens. If your pile gets too wet, which tends to happen not with freestanding piles or those in chicken wire or hardware cloth, but with the various commercial plastic or metal bins, it won’t heat up and can become anaerobic. If this happens, add dry browns and turn the pile.

If your primary source for greens is going to be grass clippings, you will have a devil of a time keeping them from matting unless you let them dry out for a day or two first.

Another factor in generating enough heat is the size of the pile. A puny pile won’t do anything and a monstrous one will be impossible to aerate and could easily become a stinky, anaerobic mess. Three feet tall and wide is good; 6 feet and you might as well buy yourself a Bobcat.

When you have the right ingredients in the proper proportions, the pile will start to heat up — the center of it should climb to 150 degrees. Once that happened to me in 10 days, but usually it takes two or three weeks. There are folks, like former North Pole farmer Ed Bostrum, who did what I consider industrial-sized composting, who could get a pile to heat up in two days, but that has never happened to me.

You want to encourage it to stay around 140 to 150 degrees for a few days, to kill pathogens and weed seeds and promote decomposition. As it starts to cool in the center, going down to 100 degrees or so, this is the signal things are done cooking. Turn the pile so that the outside materials go to the center for their turn at being heated up; you will usually end up turning the pile around every 10 days. Go through the process over and over (always checking to see if more moisture is needed) until the pile refuses to heat up and the materials have become so dark and crumbly that you cannot tell what the clumps were in their previous incarnation.

If the pile gets to 155 degrees or more, cool things down because at that point the good stuff will start dying off, too. You can lower the temperature by turning the pile, or adding water or browns.

If you have been composting for years and years, you can tell pretty much by feel when the compost is too hot, too cold or just right. If you are a newbie, however, invest in a compositing thermometer. If you can’t afford a thermometer, then turn the pile the first time about three weeks after setting it up and then every 10 days after that. Inexact, to be sure, but should work.

Some years I don’t have the time or, frankly, the inclination to worry about ratios, water, and turning. During those times, I simply switch to cold composting. Also called cool or passive composting, this technique involves finding a spot in the yard where green and brown ingredients can be dumped and left until they rot into finished compost. I still have to keep the greens and browns balanced, or else there is a diaper-pail stench emanating from that corner of the yard, but other than that I abandon it to nature. If it is early in the season and there are fewer browns available to me, I park a bale of straw nearby and periodically toss on a handful as I am emptying a tray of salad remains into the pile.

Actually, you’ll need at least two piles, since at some point you have to close off one pile or it will never finish decomposing. It can take a year to two years for a cold compost pile to be ready to use, but eventually you will end up with a wonderful product. Best of all, research shows that cool compost has more beneficial bugs and bacteria than hot compost. The trade off, of course, is that it is not as efficiently produced so you don’t have it available for your garden.

That’s it for compost until next year.