Week 17 - Composting

For episode/article 17 for This Week in the Garden, we’ll cover the basics of composting. Starting a compost pile is a great way to begin the transition from a summer garden to a fall garden. Removing old plants and adding them to a compost pile allows you to recycle the nutrients trapped in the plant material while clearing a spot in the garden for another vegetable planting.

Composting is probably something that is familiar to most people. There are two main types of compost piles, slow or cold composting and fast or hot composting. I like to think of slow composting as a set-and-forget compost pile. In this method, organic materials are added to the pile all at once, and no additional work is done to the pile. It will slowly degrade over the course of a year and the center will stay relatively cool. In a fast compost, the right mixture of materials, sizes, temperatures, and moistures must be maintained. This is a more laborious process, but you can begin using the compost in as little as three months. Most people don’t have the time or the energy to maintain a fast compost pile, so we will focus on the slow method in this episode. If you are interested in experimenting with the fast system, N.C. State has a great publication on how to set it up and maintain it.

The first step in setting up a compost pile is location. Choose a spot that is at least six feet away from your house. Make sure the location gets plenty of shade and is close to a water source, or is within reach of a hose. Shade and water are important to the microbes that will do the work degrading the organic matter you put in the pile. With the slow compost method, you don’t need to constantly water the pile, but if you get long periods of hot dry weather like we experienced in July, you may want to water the pile.

After you’ve chosen a location, you’ll need to build or buy a compost pile. They can be made out of a number of materials from wood to cinder blocks to wire. For an average size garden/yard, you’ll want a compost bin that is at least 3ft wide, deep, and tall. If you remove your grass clippings from your yard, which is not recommended for your lawn’s health, you may want a larger pile. In my garden, I used the old wire potato tower cages as my compost pile. I chose these because they are open on the sides to allow airflow, are metal, so they shouldn’t degrade like wood, and are portable. I plant on opening the cages up and spreading the compost around in the area and then moving the cages to another area the following year.

The last and most important part of slow composting is what you can and can’t put in them. N.C. State’s Backyard Compost Guide has a great list of materials that can and can’t be added to the pile. In general, plant materials such as leaves, grass clipping, and old vegetables can be added, while animal materials like old meat, fish carcasses and feces should not be added. The few exceptions to this rule are plant materials that have been sprayed with chemicals, diseased plant materials, and weeds with seeds.

Plant material that has been sprayed with pesticides has the capability to carry those chemicals over into the next year, but also have the potential to kill beneficial microbes in the pile. Most herbicides and insecticides don’t last in the environment for a long enough time for this to be a concern (because they are broken down by microbes and the sun), but it’s better to play it safe. Diseased plant material also has the potential to be transferred to your plants in the subsequent growing season. In a slow compost system, the temperature doesn’t get hot enough to kill the microbes. I’d argue that in a hot system it is unlikely that the temperatures get hot enough uniformly over the pile to kill the microbes too. For this reason, the fungi and bacteria can persist in the soil and infect future plants. The two vegetables that this is a biggest concern of are tomatoes and squash, so be cautious when composting old plants. The last exception, weed seeds, follows the same logic. In a slow system, the temperatures aren’t hot enough to kill the weeds’ seeds and if they are added to a compost pile they can sprout or they can be planted in your garden when you spread the compost in the spring. Dealing with weeds is hard enough, so there’s no reason to plant them!

Overall, composting can be as simple or as complex as gardening itself. We covered the basics of the set-and-forget slow process, but there are many more methods and issues that might come up when composting. For more information on the topic, check out our Composting Guide from the Extension Master Gardener Handbook. If you’ve got any questions or comments, send me an email or fill out our form. That’s all for this article from This Week in the Garden, stay tuned until next time.

-Adam