What is an organic fertilizer system?
It is a plan that supplies plant nutrients through organic matter and permitted amendments, while building the soil itself. The main sources are compost, manure, cover crops, crop residues and some mineral and processed amendments.
If you sell organic produce, your certifier decides which materials are allowed and what record keeping applies. This article gives concepts only, and no products or rates.
Be aware that cheaper does not always mean better and neither does more expensive. Judge sources by nutrient content, handling needs and fit with your plan. Cost categories include materials, hauling, spreading and testing.
- Compost and manure
- Cover crops and residues
- Permitted mineral amendments
- Processed materials with a label analysis
Why start with a soil test?
A soil test shows pH and nutrient levels, so you can see what is low and what is already high. Many farms have too much phosphorus and not enough of something else, and a test can prevent wasted money and runoff.
Your extension office can explain how to sample, which lab to use and how to read the report. Retest on a regular schedule and keep your results, so you can track changes.
Soil pH affects how well plants take up nutrients, so fix it based on the test, using the lime or sulfur advice from your extension office. Applying without a test wastes money and may cause harm. Soil tests also show organic matter, which tells you whether your fertility plan is building the soil or just feeding the crop each year.
- Sample the same way each time
- Use a lab recommended by extension
- Ask for organic-based recommendations when available
What do compost and manure offer?
Compost adds organic matter and a modest amount of nutrients. Manure supplies more nutrients, but its content varies by animal, bedding and how it was stored. Both need care in handling and timing.
Raw manure can carry disease organisms, and food safety guidance sets waiting periods between application and harvest for some crops. Ask your extension office for current guidance before putting manure on food crops.
Compost made from your own materials keeps costs down, but it takes time and space. Buying finished compost can fill a gap, and you can ask the supplier what went into it and whether it was tested. Bedding and feed leave their mark on manure and compost, so keep notes on what went into each batch and save samples for testing if you can.
How do cover crops and rotations fit in?
Legume cover crops host bacteria that capture nitrogen from the air, and some of it becomes available to later crops. Deep-rooted covers can bring up nutrients from lower in the soil. Rotating crops spreads nutrient demand across different plants.
Cover crop benefits vary with species, timing and weather, so treat them as one part of the plan. Match crops that need a lot of nitrogen with what came before them.
Plant tissue symptoms such as yellowing or purpling can point to a nutrient problem, but they can also come from pests, disease, weather or compaction. Confirm with a test before making changes.
How do I avoid applying too much?
Overapplication wastes money and can pollute water. Nutrients applied on frozen or saturated ground, or ahead of heavy rain, can run off. Keep applications away from wells, ditches and streams, and follow any local setback rules.
Apply based on test results and crop needs, and keep records of what you add and when. Organic sources release nutrients over time, which can make it hard to judge the amount, so go carefully and watch plant response.
Think about timing as well. Nutrients should be available when the crop needs them, and organic sources often need warm, moist soil to release nutrients, so early spring applications may act slowly.
What should I watch for with purchased amendments?
Read the product label for contents, and check that it is allowed in your organic program if you have one. Ask the supplier for a nutrient analysis. Be wary of claims that a single product replaces testing or fixes every problem.
Store amendments dry and out of reach of children and pets, and follow any handling instructions. Ask your extension office if you want an unbiased view of a product.
Keep the system simple at first. Pick one or two sources, learn how your soil responds and add more only when you see a reason.
- Pick one or two sources
- Watch plant response
- Add more only for a reason
Key takeaways
- Build fertility with compost, manure, covers and rotation, guided by soil tests.
- Raw manure needs food safety care, so check extension guidance.
- Avoid overapplication, especially near water and before heavy rain.
- Keep records and ask extension about any product claims.
Sources and further reading
Last reviewed: November 12, 2026. Written by the Homestead & Small Farm Editorial Team. See our editorial policy.