What do the N-P-K numbers on an organic fertilizer mean?

The three numbers are the percentages by weight of nitrogen (N), phosphorus (P), and potassium (K) in the bag. A product labeled 5-2-2 is 5 percent nitrogen, 2 percent phosphorus, and 2 percent potassium by weight; the rest is organic material, water, and other compounds. Nitrogen drives leaves and green growth, phosphorus supports roots, flowers, and fruit, and potassium supports overall vigor and stress tolerance. Because organic ingredients vary, most bags print an average analysis, and a soil test tells you which nutrient your garden actually needs more of.

Is organic fertilizer always safe to over-apply?

No. Organic sources release more slowly than strong synthetics, but they can still burn plants or cause nutrient problems. Blood meal is one of the highest non-synthetic nitrogen sources, and NC State Extension notes that over-application can burn plants with too much ammonia. Fresh manure can scorch roots and carry pathogens, and concentrated poultry manure can build up phosphorus over years that runs off into lakes and streams. Apply according to the soil test and bag label, water after spreading, and keep manures composted before they touch edible crops.

How quickly does organic fertilizer work?

It depends on the source. Fish emulsion and other soluble liquids act relatively quickly, within a few days to a week, and are useful for a weak or newly transplanted plant. Blood meal acts faster than most meals, while bone meal, feather meal, fish meal, kelp meal, and compost release over weeks as soil organisms decompose them. Compost and worm castings condition the soil over a whole season rather than delivering an immediate growth surge. Expect a steady, balanced response rather than the rapid green flash produced by a concentrated synthetic feed.

If I add compost to the soil, do I still need fertilizer?

Often compost alone is not enough to supply every crop's needs, because its nutrient content varies with the ingredients used. NC State Extension notes that although compost contains macro- and micronutrients, it frequently does not supply all that plants require, so lawn and garden soils should be tested and fertilized accordingly. Heavy feeders such as leafy greens, corn, and tomatoes may still need supplemental nitrogen, while root crops and fruit benefit from phosphorus and potassium. Compost builds the soil and supplies a baseline; a soil test decides whether meals, emulsions, or a balanced product are added on top.

Is manure safe for vegetable gardens?

Only when it has been composted. Extension guidance recommends using composted manure on food crops to prevent burning plants and cross-contaminating edible portions with pathogens such as E. coli. Fresh manure is high in nitrogen and salts, can scorch roots and leaves, and must be incorporated well before planting. The National Organic Program specifies a waiting period of at least 120 days between manure application and harvest for crops that touch the soil. Composted horse, poultry, rabbit, or cow manure can be mixed into beds several weeks before sowing.

What is compost tea and when should I use it?

Compost tea is a liquid extract made by steeping finished compost in non-chlorinated water so that soluble nutrients and microbes move into the water. It can be poured around the root zone as a drench or misted on leaves as a mild foliar feed. Use it between regular compost or meal applications, weekly or every two weeks, in the early morning on a cloudy day. Brew it for about 48 hours, use it within four hours of removing the compost bag, and never spray it directly on edible parts that will be eaten raw. It supports plant health and biology but does not replace a soil test or a balanced fertility program.

Organic Fertilizers: Types, N-P-K Analysis, and How to Apply Them

Organic fertilizers are plant-, animal-, or mineral-derived materials that release nitrogen, phosphorus, and potassium through the activity of soil microbes rather than dissolving into an instant chemical solution.

They feed the soil as much as they feed the plant: organic matter improves structure, water-holding capacity, and the diversity of bacteria and fungi that turn raw material into available nutrients.

This guide explains the common organic sources and their average N-P-K analysis, when and how much to apply, how they differ from synthetic fertilizers, and how to brew compost tea for a gentle soil or foliar boost.

What Organic Fertilizer Actually Does

The foundation of organic gardening is building healthy soil with a diverse microbial population, adequate organic matter, proper pH, and good fertility, rather than relying on repeated fertilizer applications.

Organic fertilizers supply the same three primary nutrients as synthetic products, but they arrive bound in organic material that must be decomposed by bacteria and fungi before roots can absorb it.

That slow release matches steady plant growth, reduces salt buildup in the root zone, and leaves behind humus that improves both clay and sandy soils.

A soil test remains the starting point for any fertility program, whether organic or conventional.

Feeds soil microbes, which in turn release nutrients to roots over weeks rather than minutes.
Adds organic matter that improves soil structure, aeration, drainage, and water-holding capacity.
Releases nutrients gradually, which lowers the risk of fertilizer burn and nutrient leaching.
Supplies secondary nutrients and trace minerals that many blended products lack.
Requires a soil test first, because organic sources vary widely in actual nutrient content.

Common Organic Fertilizers and Their Average N-P-K

The three numbers on any fertilizer label are the percentages by weight of nitrogen (N), phosphorus (P), and potassium (K).

Organic sources vary more than manufactured blends, so the figures below are average analyses from NC State Extension; actual bags can differ, and manure and compost content should be tested when accuracy matters.

Nitrogen sources drive leafy growth, phosphorus supports roots, flowers, and fruit, and potassium strengthens overall vigor and stress tolerance.

Blood meal (dried), about 10-0-0: one of the strongest non-synthetic nitrogen sources; fast enough to green up leaves, but over-application can burn plants with excess ammonia.
Bone meal (steamed), about 3-15-0 with roughly 20 percent total phosphate and 24 percent calcium: a slow phosphorus source for roots and bloom; its phosphorus is most available in soils below pH 7.
Fish emulsion, about 5-2-2 with about 5 percent sulfur: a soluble liquid fertilizer that works relatively quickly and carries a strong odor; useful as a foliar or transplant boost.
Fish meal, about 10-6-2: ground, heat-dried fish waste that releases nitrogen and phosphorus more slowly than emulsion.
Feather meal, about 11-0-0: a slow-release nitrogen source that breaks down over a long season.
Kelp meal, about 1.5-0.5-2.5 with trace minerals: dried marine algae that contributes potassium and micronutrients; often blended with fish meal to round out N-P-K.
Worm castings, about 0.5-0.5-0.3 with 50 percent organic matter and trace minerals: mild and gentle; more valued for biology and soil conditioning than for a strong nutrient dose.
Composted manure: horse manure about 1.7-0.7-1.8, poultry manure about 4-4-2, rabbit manure about 1.5-1-1; always use composted manure on crops for human consumption to avoid pathogen risk and plant burn.
Compost (commercial or homemade): analysis varies with the ingredients; it supplies organic matter, macro- and micronutrients, and biology rather than a fixed N-P-K number.
Wood ashes, about 0-2-6: supplies potash and micronutrients; do not use on acid-loving plants or tender seedlings, and apply no more than about 20 pounds per 100 square feet annually.

How Soil Microbes Turn Organic Matter into Plant Food

Organic matter does not feed a plant directly.

Bacteria, fungi, earthworms, and other soil organisms break down material through decomposition, mineralizing nitrogen and other nutrients into forms root hairs can absorb.

In clay soil, that activity builds crumb structure that opens pore spaces for air and water; in sandy soil, organic matter holds moisture and nutrients that would otherwise leach away.

A thriving microbial population also helps suppress some plant diseases and makes nutrients available over a longer window, which is why organic growers describe the practice as feeding the soil, not just the plant.

Microbes mineralize organic nitrogen into ammonium and nitrate that roots can take up.
Decomposition produces humus, which binds soil particles into a loose, workable structure.
Organic matter feeds beneficial fungi and bacteria that compete with disease organisms.
Repeated organic additions improve both drainage in heavy soil and water retention in sand.
Synthetic salts can weaken that microbial community over time, which is why organic practice emphasizes building the soil first.

When and How Much to Apply

Begin with a soil test so you add the nutrients the soil actually lacks.

Organic, slow-release materials can generally be applied once before planting and mixed thoroughly into the top several inches of soil; products such as compost, worm castings, and aged manure are usually incorporated or spread as a top dressing at this stage.

During the growing season, quick organic sources such as fish emulsion can be watered in as a side dressing around established plants, away from the stem.

Follow the bag analysis and the soil test recommendation rather than a fixed handful; because organic nutrients release slowly, a single generous dose does not produce the flashy growth of a strong synthetic application, and excess still wastes material and can run off into waterways.

Test the soil before planting; match applications to the N, P, and K recommendations on the report.
Incorporate compost, manure, bone meal, and meal-type fertilizers into the root zone before sowing or transplanting.
Use soluble liquids such as fish emulsion as a mid-season side dressing, diluted according to label.
Apply manure only after it has composted, and keep fresh manure away from edible crops.
Water after application to move nutrients into the root zone and reduce surface concentration.
Reapply on a schedule tied to crop demand: leafy greens feed more heavily on nitrogen, roots and fruit respond to phosphorus and potassium.

Organic vs. Synthetic Fertilizers

Both categories provide the same N, P, and K nutrients, and either can be used well or badly.

Manufactured blends dissolve almost immediately, so a small amount produces a fast green response, but quick-release nitrogen can burn leaves and leach through the soil after heavy rain.

Organic materials release through microbial activity, so their response develops over weeks, and they build soil biology and structure that manufactured fertilizer does not supply.

Organic blended products are sold with a printed analysis, while some materials such as soybean or alfalfa meal may be sold as animal feeds without one, which makes the soil test even more important.

Release speed: synthetics are available within days; organic sources respond over weeks as microbes decompose them.
Soil biology: organic matter feeds and shelters bacteria, fungi, and earthworms; salts in concentrated synthetics can reduce that activity.
Burn risk: slow organic sources are less likely to scorch foliage, but blood meal and concentrated manure can still burn if over-applied.
Soil structure: organic additions improve tilth in clay and sand; fertilizer alone does not change texture.
Flexibility: many gardeners combine both, using compost and organic meals before planting and dilute liquids through the season.

Homemade Compost Tea: Soil and Foliar Boost

Compost tea extracts the soluble nutrients and microbes from finished compost for a gentle soil drench or foliar spray.

NC State Extension recommends mixing one part compost with ten parts water: for one gallon, use about 13 ounces (roughly 1.5 cups) of compost.

Let tap water sit at least 24 hours to off-gas chlorine, suspend the compost in a fine mesh bag in the bucket at 60 to 80°F (16 to 27°C) out of direct sun, and stir twelve times over 48 hours or run an aquarium pump for aeration.

Remove the bag and use the tea immediately or within four hours; pour it around the root zone or spray leaves, but do not apply it to edible portions.

Spray weekly or every two weeks, early in the morning on a cloudy day before it gets hot, so ultraviolet light does not kill the beneficial microbes.

Ratio: one part finished compost to ten parts non-chlorinated water.
Brew for about 48 hours, stirring twelve times over the period or aerating continuously.
Use the tea within four hours of brewing, while microbes are still active.
Drench the soil or mist foliage; avoid spraying edible parts directly.
Apply weekly or every two weeks in the early morning or after irrigation and rain.

Related Guides

FAQ

1
What do the N-P-K numbers on an organic fertilizer mean?
The three numbers are the percentages by weight of nitrogen (N), phosphorus (P), and potassium (K) in the bag. A product labeled 5-2-2 is 5 percent nitrogen, 2 percent phosphorus, and 2 percent potassium by weight; the rest is organic material, water, and other compounds. Nitrogen drives leaves and green growth, phosphorus supports roots, flowers, and fruit, and potassium supports overall vigor and stress tolerance. Because organic ingredients vary, most bags print an average analysis, and a soil test tells you which nutrient your garden actually needs more of.
2
Is organic fertilizer always safe to over-apply?
No. Organic sources release more slowly than strong synthetics, but they can still burn plants or cause nutrient problems. Blood meal is one of the highest non-synthetic nitrogen sources, and NC State Extension notes that over-application can burn plants with too much ammonia. Fresh manure can scorch roots and carry pathogens, and concentrated poultry manure can build up phosphorus over years that runs off into lakes and streams. Apply according to the soil test and bag label, water after spreading, and keep manures composted before they touch edible crops.
3
How quickly does organic fertilizer work?
It depends on the source. Fish emulsion and other soluble liquids act relatively quickly, within a few days to a week, and are useful for a weak or newly transplanted plant. Blood meal acts faster than most meals, while bone meal, feather meal, fish meal, kelp meal, and compost release over weeks as soil organisms decompose them. Compost and worm castings condition the soil over a whole season rather than delivering an immediate growth surge. Expect a steady, balanced response rather than the rapid green flash produced by a concentrated synthetic feed.
4
If I add compost to the soil, do I still need fertilizer?
Often compost alone is not enough to supply every crop's needs, because its nutrient content varies with the ingredients used. NC State Extension notes that although compost contains macro- and micronutrients, it frequently does not supply all that plants require, so lawn and garden soils should be tested and fertilized accordingly. Heavy feeders such as leafy greens, corn, and tomatoes may still need supplemental nitrogen, while root crops and fruit benefit from phosphorus and potassium. Compost builds the soil and supplies a baseline; a soil test decides whether meals, emulsions, or a balanced product are added on top.
5
Is manure safe for vegetable gardens?
Only when it has been composted. Extension guidance recommends using composted manure on food crops to prevent burning plants and cross-contaminating edible portions with pathogens such as E. coli. Fresh manure is high in nitrogen and salts, can scorch roots and leaves, and must be incorporated well before planting. The National Organic Program specifies a waiting period of at least 120 days between manure application and harvest for crops that touch the soil. Composted horse, poultry, rabbit, or cow manure can be mixed into beds several weeks before sowing.
6
What is compost tea and when should I use it?
Compost tea is a liquid extract made by steeping finished compost in non-chlorinated water so that soluble nutrients and microbes move into the water. It can be poured around the root zone as a drench or misted on leaves as a mild foliar feed. Use it between regular compost or meal applications, weekly or every two weeks, in the early morning on a cloudy day. Brew it for about 48 hours, use it within four hours of removing the compost bag, and never spray it directly on edible parts that will be eaten raw. It supports plant health and biology but does not replace a soil test or a balanced fertility program.

Sources

NC State Extension Handbook, Chapter 17 — Organic Gardening, Organic Fertilizers Table 17-2“Blood meal (dried) 10–0–0: One of the highest non-synthetic forms of nitrogen. Over-application can burn plants with too much ammonia. Bone meal (steamed) 3–15–0; 20% total phosphate; 24% calcium. Fish emulsion 5–2–2. Fish meal 10–6–2. Kelp meal 1.5–0.5–2.5; trace minerals. Worm castings 0.5–0.5–0.3; 50% organic matter, plus trace minerals.”

NC State Extension Handbook, Chapter 17 — Organic Gardening, Soil Management and Fertility“A strong emphasis on building healthy garden soil, which has a diverse microbial population, adequate organic matter, proper pH, and good fertility... Building a nutrient reservoir into the soil, as opposed to relying heavily on fertilizer applications.”

NC State Extension Handbook, Chapter 2 — Composting, Compost Tea“Add 1 part compost to 10 parts water. For example, for 1 gallon of water (128 ounces), use 13 ounces of compost (about 1½ cups)... Stir the bucket 12 times over the next 48 hours or run an aquarium pump during that time. After 48 hours of brewing, remove the bag containing the compost... Use the tea immediately or within 4 hours after brewing. Do not use the tea on any edible portions of a plant. Spray weekly or every two weeks.”

University of New Hampshire Extension, Fertilizing Vegetable Gardens“Organic fertilizers are plant- or animal-based materials that provide these same nutrients: N, P and K... If you are using organic slow-release fertilizers, the entire amount of fertilizer that you need can be applied before planting. Make sure to incorporate it throughout the soil in the planting rows or beds, to a depth of 4-6 inches.”

NC State Extension Handbook, Chapter 2 — Composting, Benefits of Compost“Compost incorporated into the soil increases the organic matter content, improves the physical properties of the soil, helps roots penetrate more easily, holds moisture, provides aeration to plant roots, suppresses some diseases, and supplies some essential nutrients.”