One of the essential elements of a compost pile is oxygen. Without it, anaerobic decompostion sets in, and that can lead to odors and breeding grounds for unwanted pests. Properly aerated, a compost pile will of course have some odor, but not an unpleasant one - it should smell like the forest on a rainy day.

Most composting resources recommend a vent tube in the center of the pile as an excellent way to increase the oxygen content of the pile, and reduce the need to turn the pile. I followed that advice and experimented with different vent tube designs, some of which are pictured at the right. After using those tubes and more, I have concluded that a vent tube is an unnecessary inconvenience for me. However, it is very rewarding to see steam rising from the vent tube on a cool day, so you may want to use one. What follows are the results of my experimentation and a recommendation of what I think is the most practical vent tube.

Drilled PVC is commonly recommended as a good material for a vent tube. I tend to disagree, because you have to either drill many, many small holes, or a small number of large holes, and then line the interior with screening. I have seen photos of PVC tubes with just 4 or 5 small holes. Something like that appears to offer little over just a non-drilled tube that can be moved around by hand to let air in.

The first vent tube I tried was a piece of 36" wide hardware cloth with 1/2" openings. A 12" wide piece of this material with one side cut flush and the other with wire ends sticking out can be formed into a cylinder by wrapping it around 3 1/2" PVC and bending the wires to hold it together. It performs much better than any PVC tube with holes in it. However, it is fragile, and it was not long before I accidentally stepped on it and crushed it.

From there I went the PVC route, and drilled 76 3/4" holes through a 3 1/2" diameter PVC tube. Drilling all those holes took over an hour, and it was dangerous as well, because the hole saw bites into the PVC and can twists your wrist or arm. What I learned from that tube was that 3/4" holes are too large, and let the bottom of the tube fill up with material, which defeats the purpose of the vent tube.

Then I got the idea to drill a small number of big holes into PVC and line the interior with hardware cloth. The first two vent tubes are that version, with the second one cut at an angle for style. Note that those PVC tubes are 4" and have thinner walls than the 3 1/2" PVC. It is much easier to drill through, but the hole saw still can grab the material and twist your arm.

Next was even better, a tube made from PilePro material and lined with hardward cloth. For a while I deemed that the ultimate vent tube. That one is tube #3 from the left. I was happy with that design for a while, but even with 1/2" hardward cloth as a liner the bottom of the tubes still got filled up with material.

Realizing that the top of the pile would need less venting than the interior, I tried tubes that are buried within the pile. At first I attempted to vent these to the outside with small tubes thinking an input was needed. However, I now believe that the pile breathes, and that as oxygen is consumed, it is drawn in from the outside.

Without sophisticated instrumentation, it is not possible to determine the optimum volume of an interior vent. I used a drilled bucket (photographed without screen on top and inside) and a half-sized version of the wire-framed tube in a few piles but was unable to determine that one was better. Intuitively, the larger volume seems better.

However, it was after using the interior vents that I decided I do not like vent tubes. First of all, a 3' pile may or may not benefit much from venting. Again, this is something that would need a controlled laboratory environment to determine. Second, I discovered that the interior vents quickly become a habitat for cockroaches. They love the mobility within the dead air space. Rodents likely would as well, though I have not had any try to move in. (On a side note, I once built a pile on top of a screen- covered shipping pallet, to encourage bottom aeration. When I turned that pile and flipped the pallet, hundreds of roaches took off running. I do not recommend aerating your pile from the bottom with a shipping pallet!) Finally, and most important, any vent mechanism interferes with easy and proper pile building. It gets in the way and prevents radial distribution of material.

So now I use the PilePro Method to make my piles. This method creates maximum density in a ring, with less density in the center of the pile.

But back to the beginning, it is fun to watch steam rise from you piles. If you want to witness this, I recommend just a piece of PVC, undrilled, in the center of the pile. It will not fill up, and moving it around from time to time will create a void there oxygen can penetrate better into the pile. Your compost may or may not get done faster though. Anyone out there got a lab and want to experiment?