Part 4: regenerative integration

After you generate compost, how do you assess its quality and utilize it in your garden, landscape, farm, etc? Mature compost should be teeming with life and ready for application to help regenerate soil ecosystems.

Maturation

A pile cooling from around 55° C (131° F) toward ambient temperatures indicates active decomposition is slowing. You may be tempted to use this ‘young’ compost right away, but allowing a robust microorganism community to develop further should better suppress diseases (Spragge et al., 2023). If you can, let materials mature for several months to set the stage for a HIGHLY diverse and abundant biological community.

When the pile is consistently below 25° C (77 F), it is cool enough for you to consider adding red wigglers (Eisenia fetida) or other bioregionally appropriate worm species. Composting worms typically facilitate a flourishing biological community in maturing compost, but they do require thoughtful management.

The easiest mistake is to let compost get too dry, as compost worms need greater than 50% moisture (up to 70-80% moisture by weight). In fact, if compost dries out, MANY organisms will either die or go dormant (possibly reawakening in the future).

Remember that during maturation, you MUST continue shielding all life in your compost from harsh conditions. In addition to maintaining adequate moisture, ensure your pile is not getting much exposure to direct sun, wind, or extreme temperatures.

Assessment

Regardless of your maturation strategy (passive aging or compost worms), you can use common observational tools to assess compost quality: nose, fingers, and eyes, for starters. Mature compost typically smells wonderful - like the soil in a healthy forest. If you handle high-quality compost with your fingers, it will maintain a spongy structure. Look closely and it will be difficult to see individual material inputs, and it typically has a relatively deep-brown color (like dark chocolate).

Mites (Acari spp.), woodlice (Armadillidiidae spp.), springtails (Collembola spp.), and other small invertebrates will likely move into the pile and increase in number; don’t worry. But don’t feel bad about reducing populations of potentially problematic species, such as ants, centipedes, grubs, etc., especially if you spot invasive organisms. While every life form CAN serve an ecological function, we’re allowed to select the organisms we want in our compost and cultural landscapes.

If you want to expand your options, a microscope can extend your ability to see tiny organisms. Microscopes come in different types, from low-cost to expensive, and offer another way to observe stunning life forms.

For example, using a microscope to notice the abundance and variation in fungal spores and filaments (color, shape, size, etc) is useful because most fungi require oxygen. Likewise, protozoa and multicell microfauna (such as nematodes, tardigrades, microarthropods, etc.) indicate complex ecological food webs and relatively optimal environmental conditions.

A microscope is not required to assess compost quality, but it can provide a valuable check. If you have one, we recommend you use it primarily to get a general overview of the biological community (especially key bioindicators) rather than attempting to count organisms or measure populations. If you examine a compost sample and find it teeming with life at macro- and/or micro-levels, congratulations! This means your compost-making process was pretty good.

A seed-germination test is another low-cost method to assess compost safety and its potential impact on plant growth. Plants such as cucumber, watercress, and barley can be planted in a compost sample and observed for germination and growth (Lončarić et al., 2024). Normal plant growth suggests the compost is safe to use in most applications, while poor or stunted growth suggests it may contain harmful substances such as excessive nitrogen or even herbicide residues. Additional maturation may not always result in compost that is safe to use.