Getting the Right Carbon-to-Nitrogen Ratio in Your Compost
You might think composting is hard when you learn that you need to feed your compost carbon and nitrogen. And on top of that, it needs to be in the correct amounts. You're not a chemist (well, unless you are). But adjusting the carbon-to-nitrogen ratio isn't difficult.
You may hear the C:N ratio bandied about in discussions among avid composters. Decomposers that actively break down organic matter prefer a diet containing about 30 times the amount of carbon-rich material as nitrogen-rich material, or a C:N ratio of 30:1. The closer you can come to mixing up 3 parts carbon materials to one part nitrogen materials when you build your pile, the faster the decomposers will consume it and reward you with finished compost.
Actual carbon and nitrogen content in material varies, but typical ranges are included in the following table. Use them as a guide to figure proportions of browns and greens when you're mixing up a batch of compost, but don't stress over precision measurements. Blending carbon and nitrogen ingredients in the "low to middle ranges" of the C:N ratio (such as dry leaves and grass clippings) is a good starting point. Use high-carbon materials (such as cardboard and sawdust) sparingly. After you construct a few piles, you'll get the hang of mixing up your available greens and browns in appropriate amounts.
Nitrogen-rich materials still contain more carbon than nitrogen, as the following table illustrates. So combining one part nitrogen-rich materials with three (as opposed to 30) parts carbon-rich materials can get you to that 30:1 carbon-to-nitrogen ratio.
Carbon-to-Nitrogen Ratios
| Carbon-Rich Ingredients |
Carbon to Nitrogen Ratio* |
Nitrogen-Rich Ingredients |
Carbon to Nitrogen Ratio* |
| Corn stalks |
60:1 |
Chicken manure |
10:1 |
| Corrugated cardboard |
600:1 |
Coffee grounds |
20:1 |
| Dry leaves |
40–80:1 |
Garden plants and weeds |
20–35:1 |
| Mixed paper products |
200–800:1 |
Grass clippings |
10–25:1 |
| Newspaper |
150–200:1 |
Hay |
10–25:1 |
| Pine needles |
60–110:1 |
Kitchen scraps |
10–50:1 |
| Sawdust, weathered 3 years |
142:1 |
Rotted manure |
20–50:1 |
| Sawdust, weathered 2 months |
625:1 |
|
|
| Straw |
50–150:1 |
|
|
| Woody plant trimmings |
200–1,300:1 |
|
|
* Representative ranges only. Actual carbon to nitrogen ratio varies depending on such factors as plant species and material composition.
Gardening Glossary
annuals
Plants that complete their entire life cycle within one growing season. The plant germinates from seed, grows and blooms, and then produces seed and dies.
Gardening Glossary
biennials
A plant that take two growing seasons to complete its life cycle. It germinates and grows leaves and stems in the first year; produces flowers and fruit (seed) in the second, and then dies.
Gardening Glossary
bolt
When a plant flowers or produces seed prematurely.
Gardening Glossary
cold frame
A wooden or concrete block box in which you can grow plants or hold dormant during the cold winter months.
Gardening Glossary
cole crops
A family of vegetables, including broccoli, cabbage, cauliflower, kale, and Brussels sprouts. They thrive in cooler weather.
Gardening Glossary
complete fertilizer
Any fertilizer that contains all three of the primary nutrients, N-P-K (nitrogen, phosphorus, potassium). Phrase is based on regulations governing the fertilizer industry. Does not mean that the fertilizer literally contains everything a plant needs to thrive.
Gardening Glossary
deadheading
The practice of pinching or cutting off spent flowers
Gardening Glossary
evaporative-pad humidifier
A humidifier in which fans blow across a moisture-laden pad that sits in a reservoir of water.
Gardening Glossary
harden off
The process of acclimating plants grown indoors gradually to the brighter light and cooler temperatures of the outside world.
Gardening Glossary
hardiness
The ability of a plant to survive is called its hardiness.
Gardening Glossary
humus
A stable end product of organic-matter decomposition that's believed to increase microbial activity in soil, improve soil structure, and enhance the root development of plants.
Gardening Glossary
Bacillus thuringiensis Bt
An effective bacteria that attacks only the larvae of caterpillar family insects. It is safe to other insects, animals, and humans.
Gardening Glossary
macronutrients
Mineral nutrients that plants need in the largest quantities: nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur.
Gardening Glossary
mulch
Organic or inorganic material placed over the surface of soil, usually directly over the root zone of growing plants. Used to conserve moisture, kill weed seedlings, modify soil temperature, provide attractive covering to garden beds.
Gardening Glossary
organic matter
Once-living stuff like compost, sawdust, animal manure, ground bark, grass clippings, and leaf mold (composted tree leaves). Used to enrich soil and improve soil texture.
Gardening Glossary
perennials
Any plant with a life cycle of three or more years. Herbaceous (non-woody) perennials include flowering plants and herbs, mainly. Woody perennials include trees and shrubs. Longevity depends on the plant and growing conditions.
Gardening Glossary
pH
The measure of soil's acidity. Soil with low pH means it's too acidic; soil with high pH means it's alkaline. Most plants grow best in soil with a pH value between 6.5 and 7.2. Neutral soils measure 7.
Gardening Glossary
photosynthesis
The process through which plants take nutrients from the air and from the water in the soil to produce sugars that fuels the plant's growth.
Gardening Glossary
primary nutrients
Nitrogen, phosphorous, and potassium are the three nutrients plants need in the largest quantities.
Gardening Glossary
root crops
Plants with edible underground roots such as onions, carrots, beets, potatoes, turnips. Most root crops are cold-weather crops.
Gardening Glossary
self-blanching
A type of cauliflower with leaves that naturally curl over the head and exclude light. Requires cool temperatures for leaves to curl effectively.
Gardening Glossary
sets
Small onion bulbs, about 1/2-inch wide, that were started from seed the previous year. Grow onion sets with the pointy end up.
Gardening Glossary
side-dressing
The act of adding a small amount of fertilizer around or "on the side" of plants after they're growing.
Gardening Glossary
succession planting
Planting small, 2-to-4-foot patches of plants every two weeks throughout the growing season so that you can harvest a crop over an extended period of time.
Gardening Glossary
thinning
The act of cutting the least robust seedlings in your garden to give the healthier plants more room to grow.
Gardening Glossary
vining crops
Crops that grow on vines, such as cucumbers, melons, pumpkins, and winter squash. They usually require support (staking, trellising, etc.) to keep them off the ground.
