What is the Difference between Compost and Fertilizer?

picture of compost vs fertilizer
Good Food – Good Growth

Both compost and fertilizers are essential for a healthy garden. To get the best from your soil, it needs healthy organic activity and elemental chemical composition. But are the two products, compost and fertilizer, mutually exclusive?

The Merriam-Webster Dictionary defines compost as a mixture that consists largely of decayed organic matter and is used for fertilizing and conditioning land. A distinction commonly made between the two is that compost feeds the soil, and fertilizer feeds plants.

For new gardeners, the word fertilizer may imply increased soil fertility – a clever marketing ploy. Actual soil fertility produces compost that feeds the soil, increasing its capacity to manage any added chemical compounds better.  Join us as we explore both compost and fertilizer options.

“Think of fertilizer as an energy drink and compost as healthy food.”

Tony O’Neill

What is Fertilizer?

The production of fertilizer is regulated – compost net. Fertilizer that requires licensing is any substance that:

  • contains one or more recognized plant nutrients and promotes plant growth
  • or controls soil acidity
  • or alkalinity
  • or provides soil enrichment
  • or other corrective measures to the soil.

Fertilizer includes the following products:

  • mixed fertilizer
  • liming materials
  • gypsum
  • soil conditioners
  • soil amendments
  • soil additives

Unmanipulated animal or vegetable manures, peat, coconut coir, or compost do not require licensing. Any company distributing only these products would be exempt from having to obtain a fertilizer license.

As per legislation, three large numbers appear on all fertilizer labels. The first number represents nitrogen (N), the second number represents phosphate  (P) (P2O5), and the third number represents potassium (K)(K2O). These three numbers represent the primary nutrients (nitrogen(N), phosphorus(P), and potassium(K), in that order.

This marking is a national standard known as the fertilizer grade. Contained in a bag of 10-10-10 fertilizer are ten percent nitrogen, ten percent phosphate, and ten percent potash.

Combining two or more nutrient sources to make a blend, hence the name “mixed fertilizers.” For the various sorts of plants, manufacturers produce different grades.

Fertilizers with only one of each of the essential nutrients are also available. Ammonium nitrate (33.5-0-0), urea nitrogen (46-0-0), sodium nitrate (16-0-0), and liquid nitrogen are all nitrogen sources (30-0-0). Phosphorus is available in the form of 0-46-0, and potash is available in 0-0-60 or 0-0-50.

Calculating Nutrient Content

Multiply 50 by 0.10 to get the pounds of nitrogen in a 50-pound bag of 10-10-10 fertilizer. Calculate the phosphate and potash amounts in the same way.

A 50-pound bag of 10-10-10 includes 15 pounds of nutrients: 5 pounds of nitrogen, 5 pounds of phosphate, and 5 pounds of potash. Filler, commonly sand or granular limestone, makes up the remaining weight. Here’s another example

Let’s say we have a 30-lb. bag of 8-0-24 fertilizer:

  • First number (N) = 30 x .08 = 2.4 pounds of nitrogen in the 30-lbs bag
  • Second number (P) = 30 x 0. This bag has no phosphate in it.
  • Third number (K) = 30 x .24 = 7.2 pounds of pottassium – almost a quarter of the bag.

Selecting a Fertilizer Grade

The best way to select a fertilizer grade is to have your soil tested. You may also be interested in our article “9 Steps on Improving Gardens Soil Quality – FAST,” which describes the soil testing process.

 The soil test report will recommend a fertilizer grade for your use. The report also comes with a management note that provides guidelines for supplementing nitrogen for lawn and garden crops.

Nitrogen is required to grow all plant components, including the roots, leaves, stems, flowers, and fruits. Nitrogen is responsible for the green hue of plants and assists in the formation of protein. The lowest leaves turn yellow, and the entire plant turns pale green due to a shortage of nitrogen. Plants, on the other hand, are killed by too much nitrogen.

Phosphorus aids in the division of cells, the formation of roots, flowers, and fruit. Stunted growth, poor flowering, and fruiting are all symptoms of phosphorus shortage.

Many of the chemical mechanisms that allow plants to live and thrive require potassium. Potassium deficiency manifests itself in various ways, but stunted development and yellowish lower leaves are prevalent in many plants.

Consider the price per pound of nutrition when purchasing fertilizer. Fertilizers with better analysis and larger containers are generally less expensive.

I recommend a complete fertilizer with twice as much phosphorus as nitrogen or potassium for most gardeners. 10-20-10 or 12-24-12 are two examples. These fertilizers are usually easy to come by.

Some soils already have enough potassium to support plant growth and don’t require any more potassium. However, while a small amount of potassium in excess would not harm plants, it is usually recommended to use a complete fertilizer.

Don’t use lawn fertilizer in your garden beds. Lawn fertilizers have too much nitrogen in them, and many of them contain chemicals for weed management that can harm or kill plants.

Add lime to the soil that is too acidic – a pH of less than 5.7. Lime supplies calcium to the ground, making it less acidic and boosting the pH to a safe level.

Typical Fertilizer Grades 

  • 5-10-5
  • 5-10-10
  • 10-10-10
  • 8-0-24
  • 6-6-18

Spreading Fertilizer

fertilizer spreader pictogram

Lawns that are moved to create stripes, yet have different colored lanes, are most likely a product of improper fertilizer application. You will have better results if you administer your fertilizers evenly.

The two most prevalent types of fertilizer spreaders are the drop spreader and the cyclone spreader. Cyclone spreaders provide the most outstanding results. When spreading fertilizer, make sure to overlap your spread pattern by putting half of the material in one direction and the remainder in the opposite direction.

To thrive, plants require light, moisture, protection, and nutrients. If your plants aren’t growing well, fertilizing them will only help if the problem is due to a lack of nutrients. Fertilizer will not benefit plants planted in poorly drained soils, severe shade, or in competition with tree roots.

Fertilizers fall into two groups; organic and inorganic. Manure (poultry, cow, or horse), bone meal, kelp pellets, cottonseed, and other naturally occurring materials are examples of organic fertilizers. Inorganic fertilizers are synthetic fertilizers. As indicated above, organic fertilizers do not require licensing. Organic fertilizer is far less likely to cause damage to our environment.

I want to grow organic produce. May I use synthetic fertilizer?

If you want your product to be organically certified, the short answer is no; you may not use synthetic fertilizers (or herbicides or pesticides).

The foundational principle of organic gardening is that the produced product is naturally pure. Use only natural products to control the variables; ground, pests, weeds, and light.

For a product to be organically certified, the plant needs to get its nutritional supply from the growth medium directly for the duration of its life cycle. You may only add less than 20 percent nutrition can be supplied in liquid form.

Even the production process for compost you use for certified organic products is specified. Your compost pile must meet the National Organic Program (NOP) specifications if you raise certified organic crops.

The Guidelines for Organic Compost

  • A carbon to nitrogen (C:N) ratio of 15:1 to 60:1
  • A minimum temperature of 131 degrees Fahrenheit for at least three days
  • Turning or other measures sufficient to ensure that all parts of the pile reach the required temperatures
  • A minimum temperature of 131 degrees Fahrenheit for at least 15 days in systems that use windrows
  • Turning compost in systems that use windrows at least five times during the 15 days when the compost is at a minimum temperature of 131 degrees Fahrenheit
  • Compost must be cured—kept at a lower temperature for 45 days after the minimum 131 degrees Fahrenheit is met. Many state organic certifying agencies use the NOP guidelines; however, they are not the official standards. Producers should check with their certifiers about their composting plan and operation.

What are alternatives for synthetic fertilizers?

There are many organic fertilizers you can use at home such as Nettle, Comfrey and compost teas. In this article I show you how to make these at no cost to you.

Organic producers have a range of natural substances they use to increase the chemical composition of their soil. Below is a list.  If you have further suggestions, let us know.

This chart is an extract from the Potting Mixes for Certified Organic Production booklet found on the National Centre for Appropriate Technologies (NCAT) website at ATTRA.

Following are some of the booklet’s suggested mixes. Substituting coconut coir for peat moss is advisable, but then the adjustments for pH are not required. For more info, follow the link above.

Fertilizer MaterialNitrogenPhosphorusPotashReleaseComments
Alfalfa Meal2  – 31 – 22SlowSource of micronutrients
Bat Guano0 – 80 – 100 – 1Medium to FastDepending on Source
Blood Meal120 – 21 – 1Medium to Fast
Bone Meal2 – 414 – 160Slow to MediumSource of Ca (20 – 24 percent)
Cottonseed Meal4 – 62 – 31Slow to MediumAcidic
Crab Shell Meal43 – 40SlowSource of Ca (14 – 18 percent) and chitin
Feather Meal12 -1500Slow
Fish Emulsion (Liquid)2 – 53 – 41Medium to FastLiquid fertilizer, trace source of other macro-and micronutrients
Fish Meal9 – 103 – 70-1Medium to Fast
Green Sand000-5Very SlowSource of K, Mg, Fe, Si, and trace minerals
Kelp Meal10 – 12SlowSource of micronutrients
Peruvian Seabird Guano1210 – 122.5Medium to Fast
Rock Dust03 – 6Very SlowSource of Ca, Si, and trace minerals
Rock Phosphate (Calphos)0200Slow to Medium
Shrimp Meal660Slow
Soybean Meal217Slow to Medium
Sul-Po-Mag (Langbeinite)0022Slow22 percent sulfur and 11 percent magnesium
Organic Fertilizers

Seed-Starting Mixes

Seedling Mix for Styrofoam Seedling Flats

Credited to the Farm and Garden Project at the University of California, Santa Cruz

  • Two parts compost
  • Two parts peat moss
  • One part vermiculite, pre-wet

Sowing Mix

Credited to the Farm and Garden Project at the University of California, Santa Cruz

  • Five parts compost
  • Four parts soil
  • One to two parts sand
  • One to two parts leaf mold, if available
  • One part peat moss, pre-wet and sifted

Note: Sift all ingredients through a 1/4-inch screen. For every shovelful of peat, add two tablespoons of lime to offset the acidity.

Picture of compost

Growing Mixes

NOFA-NY Classic Formula for Horticultural Potting Mix

Credited to the 1992 NOFA-NY Organic Farm Certification Standards

  • 1/3 mature compost or leaf mold, sieved
  • 1/3 fine garden loam
  • 1/3 coarse sand (builder’s sand) NOFA-NY Sterile Peat-Lite Mix
  • 1/2 cubic yards shredded sphagnum peat moss
  • 1/2 cubic yards horticultural vermiculite
  • 5 pounds dried blood (12% N)
  • 10 pounds steamed bone meal
  • 5 pounds ground limestone

Eliot Coleman’s Organic Potting Mix

First published in the Winter 1994 issue of NOFA-NJ Organic News

  • 1 part sphagnum peat
  • 1 part peat humus (short fi ber)
  • 1 part compost
  • 1 part builder’s sand

To every 80 quarts of this, add:

  • 1 cup greensand
  • 1 cup colloidal phosphate
  • 1 1/2 to 2 cups crab meal or blood meal
  • 1/2 cup lime

Eliot Coleman’s Blocking Mix Recipe

Adapted from the New Organic Grower, 1995

  • Three buckets (standard 10-quart bucket) brown peat
  • 1/2 cup lime (mix well)
  • Two buckets of coarse sand or perlite
  • Three cups base fertilizer (blood meal, colloidal phosphate, and greensand mixed together in equal parts)
  • One bucket soil
  • Two buckets compost

Mix all ingredients thoroughly. Coleman does not sterilize potting soils; he believes that damp off and similar seedling problems result from overwatering, lack of air movement, not enough sun, over-fertilization, and other cultural mistakes.

What does compost do?

The regulated aerobic biological decomposition of organic waste into a stable, hummus-like product is known as composting. Composting is a solid-state fermentation process involving aerobic microorganisms that transforms various organic waste into more stable chemicals that plants can use.

The compost is the end product, and it helps to improve the physical, chemical, and microbiological aspects of the soil. In layman’s terms – compost feeds the soil.

To learn how to make quality compost that gets results every time then check out this article I wrote to make sure you not only get compost but nutrient-dense compost

Composting keeps organics out of landfills

Compostable objects do not biodegrade in landfills because organics require oxygen, water, a precise nitrogen-to-carbon ratio, and periodic mixing to be successful!

Compost reduces Greenhouse Gases

When it comes to greenhouse gases, methane is 26 times more potent than carbon dioxide. When compostables are trapped in landfills with no oxygen to help them degrade, they begin to produce methane, which can last for years slowly—as a result, composting aids in reducing greenhouse gas emissions.

Compost Creates Nutrient Rich Soil for Landscaping and Gardening

Composting aids in the creation of nutrient-rich soils (in your backyard or through industrial processes). Composting soil can be pretty beneficial to your garden, allowing your vegetables to grow large and robust.

Composting can reduce your trash bill

You can lower your garbage bill if you live in a “Pay-As-You-Throw” neighborhood, such as Boulder. You can acquire a smaller rubbish container because you’ll be composting the organics you used to throw away. If you are unable to do it yourself, consider taking it to a community composting center.

How can I boost my composts fertility?

As you will see from my YouTube channel, I reuse my compost again and again. Please take a look at the video below to see how I do it.




Though compost can act as an initial fertilizer, the continued nutrient consumption of plants will, over time, deplete the available resources. Adding slow-releasing, organic fertilizer to your garden is the solution. If you opt for synthetic fertilizers, please read the instructions on the packaging carefully and don’t exceed the recommended dosage.

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Tony O'Neill

I am Tony O'Neill, A full-time firefighter, and professional gardener. I have spent most of my life gardening. From the age of 7 until the present day at 46. My goal is to use my love and knowledge of gardening to support you and to simplify the gardening process so you are more productive

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