Consulting Engineering

Greenville, South Carolina

There are so many imperatives to sustainable gardening that you might be reluctant to name the one thing that is most important. However, the soil is literally and figuratively the foundation of the garden upon which everything else stands. And, if a garden is truly "sustainable", the composting system provides all of the nutrients that plants need without chemical fertilizer. This is what primarily makes the garden sustainable: all of the garden "waste" (clippings, vines, leaves, rotting fruit, etc.) along with your table food scraps (other than meat and grease) and yard waste (leaves, grass clippings, pruning scraps) are composted to create the soil that starts the growing process again-- nature is inherently cyclical in this way!.... We have experimented with several composting methods though the years, but the process and components described on this page are what we have evolved to at this point and which seem to work well for maintaining a consistent and balanced soil. But, don't be intimidated; once you get it up and going, you will find it easy to maintain, will enjoy being a soil "cook", and will be convinced of its value!

Composting

There are many composting methods and devices, but the purpose of each is the same: to generate a balanced, nutrient-rich soil or soil amendment. Many people are advocates of the single compost "pile" in which all of the composted materials are kept and constantly turned in a single stage of sorts. We find this method to be problematic for various reasons, not the least of which is the difficulty in turning (and thereby maintaining consistency) and the problems with critters getting into and removing rotting food stuffs. The system we employ involves two stages: the closed composting tumbler and the closed storage bin.

The tumbler is where the compost is actually "made" by combining already-composting "browns" (leaves and yard waste from a pile you maintain on the ground) with "greens" (food scraps and anything green that has not yet begun to decompose) into a dark-colored, closed container that can be rotated daily. Composting is an aerobic process by which the organic matter is broken down under elevated temperatures. This is why the tumbler is ideal for rapid creation of finished compost: the tumbling better exposes the contents to air (as long as you tumble daily), and the dark container absorbs radiation which makes the unit into something of a better oven. Also, it is not as tricky to get the exact proportion of browns and greens. Simply start by filling the tumbler about half full with contents from your "browns" yard pile. Then daily add your "green" food scraps and tumble 3-4 revolutions. You will know the compost is ready to be used (or, better, stored) when it is a consistent, almost black color. In colder weather this process will take longer, but in the summer it usually only takes about 2-3 weeks depending on whether your tumbler gets direct sunlight. One BIG pointer here: be a leaf hog-- gather every leaf you can in the fall and run it through your mower before you put it on your pile-- you can never have too much leaf mulch in your brown pile; it is like composting "gold" and you will use a lot of it!!

We find it best to put all table food scraps in a container stored in the freezer like this gallon ice cream bucket. Dump this daily into your tumbler and then tumble. Keeping it in the freezer will keep scraps from smelling while in the house.

1. Compost Tumbler

The "browns" yard waste pile can be kept open on the ground since animals won't bother it. It is best that anything you put on the pile is cut into fairly small pieces. We find that running everything through the mower first is ideal. And, for material like limbs that won't go through the mower, run them through a chipper or don't use them for compost. Also, there is no real need to turn this pile because it eventually gets mixed well in the tumbler.

Constructing the tumbler.....

2. Storage Bin

Tumbler units can be purchased for about $100 and may be cheaper in the end when you factor the time to construct a home-made device. However, we built ours because we haven't found any to buy that meet our specific desires, particularly something that is quite as permanent. So, if you want to copy ours, the basic instructions are as follows (which are likely mostly self-evident in looking at the pictures):

1. Acquire a black, plastic "food-grade" container such as a 55-gallon pickle barrel (do NOT use anything other than a new container or one used to store food). Usually you can find one for free or really cheap; check on Craigslist.
2. Install two upright supports in the ground as shown in the pictures. You can use pressure-treated lumber (4x4 or angled 2x4's ). Set the top of each upright level to each other and at a height that will provide enough clearance to get your wheelbarrow under the tumbler when you dump. Make the uprights solid by burying them adequately and by pouring some Sakrete 10"-12" around the grade line. Also, make sure they are far enough apart to install the container in a horizontal orientation.
3. Cut a rectangular door in the container (see pictures) and install two top hinges (outdoor type), two side latches (make sure these are heavy-duty because they will have to support the weight of the contents when you tumble), and a handle.
4. Cut holes in the center of either end of the container just big enough to slide the shaft (coordinate with step 5). Note that the top of most of these containers is thin plastic, so you will want to install some additional bearing plates on the inside and outside of the plastic (see picture below) or else the plastic will eventually break under the constant load. Because the plastic on the bottom of the container is thick, no bearing plate is necessary on the bottom.
5. Cut the shaft to the necessary length based on your upright spacing. We used 3/4" EMT which can be purchased cheaply at a home center and is galvanized for corrosion protection (note that they keep this in the electrical section as it is metal conduit).
6. Slide the container onto the shaft and install the assembly onto the uprights using long exterior wood screws on each end. Make sure to drill the top-centered holes in the shaft before hauling everything to the uprights.
7. Install three 3/4" PVC schedule 40 pipe handles as shown for making the tumbling easier (you might be tempted not to bother with this especially if your container has grip indentions; but, you will find that a nearly-pregnant tumbler is really difficult to turn without them-- believe us, you will eventually add them if you do not install them to begin with). Study the picture below to see how this is generally done-- it involves drilling holes and driving screws through the pipe and into the bearing plates.
8. Create a flat, smooth surface below the tumbler for dumping the contents and shoveling. We spread a little Sakrete below ours.

A compost tumbler by itself is unlikely to be adequate unless your use of the compost is frequent and is only needed as a soil amendment (i.e., a fertilizer in existing soil). However, for most gardens, like ours, the compost is mixed with other components to create the replacement soil for the beds, and it is generally only needed at season changes when beds are being tilled, filled/topped-off and re-planted. For this reason, we find it necessary to maintain a storage bin to collect all of the compost we generate in the tumblers (and we currently maintain three tumblers to meet all of our needs). Also, the storage bin allows you to mix the compost with other components that make it adequate as a complete bed soil, and it also makes it much more uniform. For example, the mass that typically comes directly out of the tumbler is essentially all organic matter; when it dries out (and it dries quickly), it tends to become a hard, solid mass (almost like it is glued) that can create a hostile condition for plant roots. Also, the chemical composition of each tumbler batch will vary depending on what you are putting in the tumbler at a given period-- some batches will be more nutrient-rich than others. So, by collecting multiple compost batches, you can mix them together and add components such as some sand, ashes, clay-laden existing soil, vermiculite (or other moisture-holding material), etc. to create your own soil recipe for the ideal soil (i.e., nutrient rich, friable, moisture-holding). And, if you are really serious, you can have your bin content tested to make sure it has the right pH balance and mineral composition for ideal plant growth. Now, there is one other thing you might be wondering: aren't the contents in a storage bin hard to mix just like with a big compost pile system? The answer is: no, not really. First of all, it isn't necessary to turn all of the contents completely like in a primary compost device. And, the mixture of compost and additions is made up of tiny pieces which mix pretty easily by running the shovel around and through the mass-- you don't have to lift and turn everything.

There are a few things to consider for a storage bin:
1. The bin must have a securely closing lid such that animals and reptiles (think snakes) won't get into it--and they WILL if you don't make it tight.
2. Construct or buy your bin with a material that won't rot. We used OSB sheets and lumber to construct ours (which will rot, of course), but we applied a non-toxic exterior seal to everything and lined the insides with plastic.
3. Provide enough volume in the bin to store about 10-12 tumbler loads and the other additions. Keep in mind that each tumbler load will shrink a great deal by the time you dump it, and the compost will continue to shrink in the storage bin. So the bin doesn't have to be as big as you think. For storing the on-going production of three 55-gallon tumblers, our bin measures 3'Wx5'Lx30"H (~38 cubic feet).
4. Make the depth of the bin and the open top of the bin accessible for working in it. If the bin is too deep, you might not be able to reach the bottom easily. And, you want to be able to get to all parts of the pile pretty easily for mixing and working. So, while a big plastic garbage can might seem like a good storage bin, it won't work well for all of these reasons.
5. Put drain holes in the bottom of your bin. While the contents do need to always be moist (which they will naturally), you don't want bulk water to collect. The bottom of our bin is actually concrete (four 80-lb bags of Sakrete, actually) with holes we cast when we poured it-- see the picture on the right.
6. Don't freak out by what is in your bin, especially in the summer. First of all, if you have a healthy bin, it will be LOADED with earth worms (you really want this-- see the fuzzy picture of ours on the right). But, at various times, you will also have an abundance of insect life (I won't go into detail here, but it can get interesting).
7. Keep a manure-bedding fork and a shovel near your operation for convenience as you will need them frequently.
8. Yes, you can do this!!!