Compost maturity: when is it ready to apply?
Life continues to develop after the hot phase. Curing management and microscopy help us assess the compost we will transfer to soil.
A pile cooling marks an important stage, but readiness also depends on what happened earlier and what is happening inside. The Soil Food Web School considers the height and duration of temperatures, turning and the community that developed. A rich community of bacteria, fungi, protozoa and nematodes takes time.
From heating to curing
Microbial activity generates heat. When easily decomposable materials decline, heat production falls and the pile cools. Slower decomposition continues, with organisms favouring milder temperatures taking on a larger role. Curing is an essential production stage.
A cold pile may still be immature
Cooling can indicate progress or reduced activity caused by dryness. Cornell identifies an early temperature fall accompanied by dry material as a possible moisture shortage. Monitor temperature, moisture and structure together. Strong reheating after turning and restoring conditions means more time is needed; SARE uses reheating as an indication of incomplete processing.
Maintaining life during curing
The pile still needs water and oxygen. Excess drying restricts activity; excess water blocks air-filled pores. Material structure supports aerobic conditions. Turning needs usually decline as decomposition and oxygen demand ease. Intervene according to observations rather than mechanically continuing the hot-phase schedule.
What microscopy shows
In Dr Elaine Ingham’s approach, compost transfers microorganisms into soil. Assessment therefore includes its biology. The School describes examination before application to assess major groups and whether the community meets the objective. Preparation and management connect with biological results.
The thermometer records temperature history; the microscope adds a community picture. These are complementary observations.
When to apply
Assess the batch: has the active hot phase finished? Does temperature remain near ambient with suitable moisture and aeration? Has there been time for curing? What does microscopy show? The School combines time, temperature and turning records with biological criteria. Both processing and community development matter.
Our field work
We follow piles and examine compost biology, evaluating each batch for soil application or the preparation of extracts and teas.