How to Choose the Right Compost for You (5 Important Properties to Consider)

Compost is a natural supplement commonly added to boost the vitality of plants. It is produced with different ingredients such as wood chips, coffee grounds, and food waste using a variety of methods such as worms (vermicomposting), anaerobic and aerobic processes to break down materials. If the composting process is incomplete or done incorrectly, the compost will contain harmful weed seeds and pathogens. Given that not all compost is created equal, it is important that we examine and educate ourselves on the key properties of compost in order to select the mixture that is most suitable for our planting needs. Soil Social conducts rigorous scientific testing on the following 5 important properties of compost to ensure an optimal outcome.

Our compost

1. Biodiversity level

According to Dr. Elaine Ingham who pioneered the Soil Food Web Approach, good compost needs to have a bustling ecosystem of microorganisms such as bacteria and fungi, as well as small critters such as arthropods. These organisms are critical in breaking down organic matter and converting it to available forms that plants can absorb. Thus, a compost should not be dead but instead, be rich with life that is visible to the naked eye and when viewed under the microscope. If you happen to see some of these organisms such as woodlice and millipedes, do not be afraid as they are a good indicator of a biodiverse and nutrient-rich compost.

2. Electrical Conductivity (from good salts)

This test is performed to assess the level of ions that is present in the compost. Usually, a high value represents good levels of positive ions like calcium, magnesium and potassium. These ions are essential for plant growth and reproduction. However, there is a caveat when conducting this test: a high value may be indicative of high sodium levels (which is a cause for concern). High sodium impairs the plant’s ability to uptake water and eventually wilt. Further lab tests will have to be performed to investigate the identities of these ions.

Testing the electrical conductivity level of our compost sample

3. Fungal-Bacterial Ratio

The soil in different environments often possesses different fungal biomass to bacterial biomass ratios. The fungal-bacterial ratio is a good indicator of what types of plants should be planted in that soil. As fungi release ammonium when feeding, this results in ammonium-rich soil which wood plants prefer. Conversely, bacteria expel nitrates when feeding, producing nitrate-rich soil in which leafy vegetables thrive.

Leafy vegetable plants thrive in bacterial-dominated soil (1-to-2 ratio). Most plants that we deal with, like herbs and fruiting plants, favour a 1-to-1 ratio of both fungi and bacteria.

4. Nitrate Level

Nitrate is one form of nitrogen that is readily absorbed by plants, aside from ammonium. As mentioned above, nitrates are abundant in bacteria-rich compost and are beneficial for leafy plants. Being a nitrogen source, nitrates are crucial in every stage of a plant’s development as it is a component of DNA and enzymes. Generally, fruiting plants love a moderate amount of nitrates but when in excess, results in the plant producing many leaves but no fruits.

5. pH Level

Most plants generally favour a somewhat neutral pH level of soil (6.0 - 7.5). The pH levels of soil also inform us of whether the soil is fungi or bacteria-rich, allowing us to calculate its fungal-bacterial ratio. Fungi are able to grow in a wide range of pH levels as they are usually unaffected by pH levels. On the contrary, bacteria thrive in slightly alkaline soil (about pH 8.0), indicated by their high diversity and abundance at that pH level.

Testing the pH level of our compost sample


By conducting these tests and analyses, we are able to take a calculated science-based approach toward compost making, thereby allowing us to create compost solutions that meet the varying needs of our customers.

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