By Sam Burbach, Education & Programming Coordinator – 05/21/2020
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Many gardeners know compost to be black gold for the garden. In its most basic definition, compost is decayed organic matter. Compost can be purchased or, better yet, created at home. Not only is compost a nutrient-rich natural amendment to feed your soil but it is also a great way to use your kitchen and yard waste and keep it out of the landfill.
All composting requires four basic things: organic matter, moisture, oxygen, and bacteria.
Here is quick overview of each:
- Organic matter: The organic matter collected for compost can be categorized as brown organic matter, such as dead leaves, twigs, and paper products, or green organic matter, such as food scraps and lawn clippings. Both types of organic matter are needed since brown materials provide carbon and green materials provide nitrogen.
- Moisture: Water helps speed up the composting process, so you want your compost to remain evenly moist but not too wet. If there is too much water, it will take away space for oxygen.
- Oxygen: For good quality compost, we need oxygen so that aerobic microorganisms (bacteria, fungi, mold and yeast that require oxygen) break the compost down because they do it efficiently and excrete nutrients such as nitrogen, phosphorus, and magnesium which are all needed by plants. If there is no oxygen present, anaerobic microorganisms will consume the compost, which they do not do as efficiently as aerobes and they can produce chemicals that are not beneficial to plants and often result in bad odors.
- Bacteria: Microorganisms, primarily bacteria, in the soil are responsible for breaking down the organic matter into compost. Bacteria and other microorganisms, such as fungi, get assistance in breaking down the larger materials from larger organisms, such as insects and worms, as well.
There are three basic categories for compost – cold/slow, hot/fast, and worm-based/vermicompost.
Here is a quick overview of each method:
- Cold/slow composting: Compost materials are broken down slowly because very little effort goes into maintaining the compost pile. It could take up to a year or two for the materials to decompose but it also requires the least amount of work.
- Hot/fast composting: Compost materials are broken down quickly and the compost pile is manipulated by turning frequently to reach high temperatures (ideally at least 130 degrees F) in order to kill weed seeds and plant pathogens. You get compost the fastest with this method but it also requires the most work.
- Vermicomposting: Food scraps are broken down by worms feeding on them in a worm bin. Worms create great quality compost but the worm bin needs care and the worms need to be taken out of the finished compost and placed back in the bin before adding the compost to the garden.
Your garden will benefit from any method of composting you choose, but I am going to focus on composting food/kitchen scraps (rather than yard waste) using a method of cold/slow composting. I want to talk about composting directly into the garden through in-situ or in-place composting. Why have I chosen this method to use at home? 1) I want to put my food scraps to good use – reaping the benefits of their nutrients for my garden while also keeping them out of the landfill. 2) I simply do not want to maintain a compost pile or worm bin.
In-place composting (or trench composting if used on a larger scale) is exactly what it sounds like – you dig a hole in the place that you want the compost, throw in your organic material, cover it up with soil, and let it all decompose over time. A large trench can be dug for yard waste to be thrown in throughout the growing season and covered at the end of the season, but with food scraps, digging smaller holes will work best because you want to cover the food scraps right away to keep critters away.
So how can you compost directly in your garden? Collect food scraps (no meat, fish, dairy, or fats/oils) and even used paper towels/napkins (so long as they’re not covered in oils or fats) from the kitchen, find a vacant spot in your garden, dig a hole at least 12 inches deep and wide enough to hold all of the scraps keeping them no more than 4 inches thick, and then fill the hole back in with soil. The food scraps (green matter) and paper products (brown matter) will break down directly in the garden and the nutrients will become available for the plants to use with very little work required.
Native Americans used a version of this when they would bury fish scraps underneath corn crops to provide nutrients to the plant as the fish decomposed. I’ve read mixed research as to whether you can bury your scraps and then plant directly above them at the same time, or if you should wait a few weeks for the scraps to decompose before planting above them. If we think about the composting process, oxygen is required by the microorganisms to decompose the organic matter so we may deprive plant roots of oxygen if we plant directly on top of a compost hole that is still breaking down. Waiting at least 2-4 weeks before planting directly above a compost hole may be the safest choice for the plant’s health.
There are a few drawbacks to in-place composting to consider. First, we can only use this method when the ground is workable, so in our Midwest winters we won’t be able to bury kitchen scraps when the ground is frozen. Second, it can take anywhere from a few weeks to a few months for the organic matter to fully break down depending on the conditions, so we will have to wait a couple weeks before planting on top of that location. Third, if you have a small garden, you may run out of spaces quickly if you are adding your kitchen scraps every day or so.
If this sounds like a version of composting that is suited for you, here’s how to get started!
What to Compost:
- Fruit and vegetable scraps
- Egg shells (bake in a 200 degree oven for about 20-30 minutes to dry out and then crush into small pieces so they break down faster in the garden)
- Used coffee grounds (and filters if you’d like)
- Tea bags (removing any small staples or other non-compostable parts)
- Nut shells with any salt washed off (except walnut shells – these contain the chemical juglone which is toxic to some plants, especially tomatoes)
- Used paper towels or paper napkins (if they’re not covered in oils/fats from your food)
- Cardboard tube from paper towels/toilet paper or paper grocery bags torn into small pieces
How to Compost:
- Collect kitchen scraps (no meat, fish, dairy, or fats/oils) until you are ready to bury them. I use an empty plastic container with a lid so that I can collect scraps throughout the day without any odors. I have even collected scraps over the course of a couple days when the weather was not favorable to bury the scraps or when I didn’t have an amount of scraps that I felt was large enough to bury and found no odors, but be careful of moisture levels in a closed container so that mold does not grow.
- Find a place in your garden to bury your scraps. If you are doing this in a garden bed that hasn’t been planted yet, you can simply pick any spot to start. You can start at one end of the garden and work your way to the other digging holes every day or two, or start where you plan to plant first so that the organic matter has some time to break down before you plant there (wait about 2-4 weeks) and then work your way to where you’ll be planting later. Once you’ve planted in a garden, feel free to continue to compost with this method, just place your hole outside of the root-zone of any of your growing plants so you don’t damage the roots with your shovel (think at least 8-12 inches, or more depending on the size of your plant, away from the crown of the plant to be safe). You can do this in vegetable beds or even in your ornamental garden beds.
- Dig a hole at least 12-inches deep and as wide as you think is necessary to throw in your scraps, keeping them about 4-inches thick. If you have a lot of scraps, you can dig a trench to cover one large area or dig multiple smaller holes to spread it all out.
- Place the scraps you have collected in the hole you have dug.
- Cover the organic matter with about 6-8 inches of soil, and water the area. Keep the soil moist to aid in the composting process and speed up the breakdown of the organic matter.
A Few Tips:
- As soon as the soil is workable in the spring, start adding in-place compost holes to your vegetable garden so that the organic matter has time to break down before you plant most of your crops.
- Continue to add compost to the garden through fall until the soil is no longer workable so that the organic matter will have all winter to break down and will be ready by spring.
- Chop your kitchen scraps up into small pieces or throw them in a blender so that they will decompose faster.
- If you have a site where you plan to plant a tree or shrub the following spring, start an in-place compost hole during the summer or fall prior to planting so that the site will have nice fertile soil to plant in when you’re ready.