The Truth About Organic Fertilizers: What We Actually Use at Farmsustaina

There is a persistent belief in organic gardening circles that fertiliser use is either unnecessary or somehow philosophically at odds with organic principles. This is not quite right, and getting it wrong leads to either under-fed plants or over-fed ones. Here is an honest account of what we actually use at Farmsustaina, why we use it, and what we have learned about getting organic nitrogen management right.

Why organic nitrogen is slower — and why that matters

Organic nitrogen sources — blood meal, fish meal, feather meal, compost — are not immediately plant-available. They must be broken down by soil microorganisms before plants can use them. This takes time, typically 2–4 weeks depending on soil temperature and moisture. The implication is that organic fertilisers need to be applied in anticipation of need, not in response to deficiency. If you apply blood meal when a plant is already showing nitrogen stress, you will not solve the problem quickly. Understanding this changes when and how you apply organic inputs.

Blood meal: high nitrogen, use carefully

Blood meal is one of the fastest-acting organic nitrogen sources, with an NPK of approximately 12-0-0. It is useful for leafy crops with high nitrogen demand — kale, Swiss chard, amaranth — applied early in the season before rapid growth begins. The risk is over-application. Too much nitrogen, applied too late, pushes lush top growth at the expense of root development, fruit set, and disease resistance. We use blood meal sparingly and only on beds intended for high-nitrogen leafy crops. We do not apply it to fruiting crops like tomatoes and peppers after transplanting.

Insect frass: balanced and biologically active

Insect frass — the excrement and exoskeleton material of farmed insects, typically black soldier fly larvae — is a relatively recent addition to the organic grower’s toolkit and a genuinely excellent one. Its NPK is modest, typically around 3-2-2, but its value goes beyond the numbers. Frass contains chitin, which triggers plant immune responses and has been shown to improve resistance to certain pathogens and pests. It also contains a diverse microbial population that benefits soil biology. We use it as a soil drench and top dressing on transplant beds, where the plant immunity benefits are particularly useful during establishment stress.

Compost: the foundation of everything

Compost is not a fertiliser in the conventional sense. It does not have a dramatic NPK. What it does is build the soil system that makes all other inputs more effective — and reduces the amount of additional input required over time. Every bed at Farmsustaina receives compost before each planting. Beds that have been amended annually for multiple years need significantly less supplemental fertility than newer beds because the soil biology and organic matter are doing more of the work.

How much plants actually need

Less than most gardeners think, if soil biology is healthy. The most common mistake is applying organic fertilisers on the same schedule as synthetic ones — which leads to over-application and, in some cases, nutrient toxicity or imbalance. A soil test every two or three years gives a far more reliable picture of what a specific bed actually needs than any general recommendation. We use soil tests to guide amendment decisions and have found, consistently, that well-composted beds require less supplemental input than their appearance might suggest.

Common mistakes

Applying high-nitrogen inputs too late in the season. Adding amendments without a soil test and creating phosphorus or potassium excess that locks out other nutrients. Using blood meal on fruiting crops after they have set flowers — which pushes vegetative growth at the expense of fruit. Applying compost that is not fully finished, which can tie up nitrogen during decomposition. And treating organic fertilisers as interchangeable with synthetic ones in terms of timing and application rate, which they are not.

Farmsustaina – Rooted in Nature, Rich in Health – Farm-Fresh & Organic!