University of Maryland Extension

What compost should I use?

Author: 
Neith Little

Choosing the right compost depends on what you plan to use it for.

If you are adding compost to increase the organic matter of your soil, plant-based composts are good choice because they will have relatively high carbon.

If you are adding compost to provide nutrients to your plants, you will need to look for a compost with a low C:N ratio, and with an N:P:K analysis on the label. A C:N ratio above 25 means that the compost is likely to bind up nitrogen in your soil as it decomposes. Generally, if you want the compost to provide nutrients to your plants, you will need to find a composted manure. Many yard-waste composts have less than 1% nitrogen, phosphorus, and potassium by weight. Some composted manures are 2-5% nitrogen, phosphorus, and potassium by weight.

If you will be using the compost in a high tunnel, or in another situation where rain will not fall on the soil, you should also look for a compost with a low salinity analysis. If you are using the compost outdoors, salinity does not matter as much.

This article from Missouri Extension has more helpful information on interpreting the results of a compost analysis: https://extension2.missouri.edu/programs/soil-and-plant-testing-laboratory/spl-compost-analysis

If you are planning to use compost as part of the mix for filling a raised bed, please refer to this article: https://extension.umd.edu/hgic/topics/soil-fill-raised-beds

If you are selling what you grow, note that in Maryland farmers who sell at least $2,500 gross per year are required to follow a certified nutrient management plan. More information on how to get a nutrient management plan is available here: https://extension.umd.edu/anmp

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