Many growers find themselves confused by all of the different fertilizer labels found at their local hydroponics shop. For some growers, deciphering the percentages of essential elements is an important part of building an optimal feeding regimen.

Although indoor gardening products are mostly unique to indoor horticulture, they are still considered agricultural fertilizers by the government. This means all fertilizer products sold through hydro retailers must meet or exceed state requirements for fertilizer labeling.

The Association of American Plant Food Control Officials (AAPFCO) is the main entity responsible for finding uniformity among state regulations and providing a national standard for fertilizer labeling. Most growers have probably never even heard of the AAPFCO, but it is the best reference for helping us all understand individual state fertilizer laws and regulations.


The AAPFCO’s beginnings can be traced back to the late 1800s when Massachusetts enacted the first fertilizer control law in the United States. By 1947, all but one of the lower 48 states had created laws that regulated the distribution and use of fertilizer products.

Most of the original fertilizer laws were non-uniform and caused great confusion for fertilizer producers trying to distribute products in more than one state. Most of the early laws also failed to regulate the labeling process that helps prevent misbranding and adulteration. It became necessary to develop uniform enforcement for the protection of both consumers and the industry.

In the early days, the AAPFCO was known as the Association of Official Agricultural Chemists (AOAC) and its members were in charge of the regulations for fertilizers in their respective states. These chemists discussed the vast differences in state laws and the reliability of laboratory methods.

The original objective of the AOAC was to “secure as far as possible uniformity in legislation.” In 1965, the AOAC become the AAPFCO. Active membership in the association is open to each state and territory in North America.

The AAPFCO is governed by a board of directors that handles the day-to-day activities of the association and makes recommendations to members based on ideas developed by the association’s committees.

National Standard Label

One of the most important results of the AAPFCO’s efforts to create uniformity in the industry is the Uniform State Fertilizer Bill. The Uniform State Fertilizer Bill is legislation all states can use to enact the same basic requirements for fertilizer labeling. The Uniform State Fertilizer Bill essentially created a national standard for labels on all fertilizers intended for sale.

To meet standard label requirements, a fertilizer label must appear in a readable and conspicuous form on either the front of the package, on the upper third of a side of a package, or on a tag attached to the package. For bulk products, the label information, in written or printed form, must accompany the delivery and be supplied to the purchaser at the time of delivery.

Each fertilizer label must also contain five key components: the brand, the grade, a guaranteed analysis, the net weight and the name and address of the registrant or licensee. In addition to these five key components, many fertilizer labels include product derivatives, directions for use, beneficial substances and a reference for trace metals analysis.

The Brand

The brand of a fertilizer is any term, design or trademark used in connection with one or multiple grades of fertilizer. The brand cannot be considered misleading in any way. For example, a company cannot brand their product as a “nitrogen blaster” if it contains no nitrogen because this would be misleading. Numerals in the brand that could be considered misleading are also prohibited. In other words, a brand cannot be named “N-20” if the percentage of available nitrogen is only 5% because the brand name could make people think the product contained 20% nitrogen.

The Grade

The grade is essentially the abbreviated representation of the guarantees for total nitrogen (N), phosphorus (P) and soluble potassium (K). These numbers are always separated by a hyphen. For example, if a fertilizer’s N-P-K is 20-20-20, the 20-20-20 is considered the grade on the fertilizer label. The grade essentially gives growers the ratio between the three key nutrients found in the fertilizer.

Guaranteed Analysis

A guaranteed analysis is a listed breakdown of percentages of particular nutrients contained in a fertilizer. A guaranteed analysis on a fertilizer label must follow a specific order and format. The guaranteed analysis includes the available percentages of nitrogen, phosphate, soluble potash, calcium, magnesium, sulfur, boron, chlorine, cobalt, copper, iron, manganese, molybdenum, sodium and zinc. Nitrogen is usually broken down further into the total percentages of ammoniacal nitrogen, nitrate nitrogen and other determinable forms of nitrogen.

Product Derivatives

Many fertilizer companies will include a derivation statement on the fertilizer label. This should always appear right after the guaranteed analysis. This statement is not required by the Uniform State Fertilizer Bill but can be required by individual states to be included in fertilizer labeling. Product derivatives can appear as a name of a chemical compound (ammonium phosphate) or as an organic ingredient (bat guano).

Net Weight

All fertilizers (dry and liquid) should be sold on the basis of net weight. The net weight may be expressed in metric units.

Directions for Use

Fertilizers intended for distribution to end users should always include directions for use. The minimum directions must include either a general statement, such as “use in accordance with the recommendations of a qualified individual,” or the label must provide detailed instructions for use.

Name and Address of the Registrant or Licensee

The person or the company responsible for the guarantees on the label must be listed. If a company makes a claim on a label, it must be able to guarantee that claim.

Beneficial Substances

The term “beneficial substance” refers to a substance or compound, other than primary, secondary or micronutrients, which is demonstrated by scientific research to be beneficial to one or more species of plants. Two common examples of beneficial substances a gardener might find in a local hydroponics retail store are silica and beneficial micro-organisms. Fertilizers made entirely of or containing beneficial substances must include the phrase “contains beneficial substances” on the label. A percentage or weight of each beneficial substance should also be included.

Trace Metals

In addition to the national standard, some states have adopted standards regulating trace metal content in fertilizers. Some states even require further analysis results to verify the amounts of the trace metals. Currently, the three states that have publicly posted the submitted analysis for products are California, Washington and Oregon. Growers can visit each state’s website to find out the exact percentages of trace metals in a particular fertilizer or additive. You might have to dig deep, but the information is there.

State Regulations

Regardless of the recommendations made by the AAPFCO, each state governs its own agricultural products. California, Washington and Oregon have the strictest regulations regarding fertilizers sold for indoor horticultural purposes. Because of this, many of the fertilizer companies involved with indoor horticulture will get their products registered in these states first, knowing state requirements are not as strict.

However, each state is different, so growers and fertilizer producers should always carefully examine regulations for their state or the states in which they wish to distribute products. The AAPFCO has the most comprehensive compilation of state fertilizer laws and regulations, which can be found on its website.

Final Thoughts

Thanks to the AAPFCO, understanding fertilizer labeling is a little less confusing and a little more uniform. However, the fact that every state in the country has its own agricultural entity that oversees fertilizer labeling and registration means things can still be overwhelming.

The good news is most hobby growers purchase fertilizers from the same state time after time, which means the products they purchase are regulated by the same entity. This does not mean that each fertilizer company uses the same ingredients to derive its guaranteed analysis.

Different products with the exact same guaranteed analysis percentages of nutrients can still provide widely varied results because various sources of nutrients can affect the way particular plant species respond.

In other words, don’t expect every fertilizer with a 5-5-5 grade to perform the same. The actual product derivatives and the particular plant species will always play a role in the way a fertilizer performs.

In the end, it is best to contact the fertilizer manufacturer directly if you have any questions or concerns regarding a product’s guaranteed analysis and recommended use.

A common practice for indoor gardeners is to mix and match fertilizers and additives, which makes it even more difficult to determine the exact proportions of particular nutrients being fed to plants.

Contents of a fertilizer regimen can be complex and seem to require a master’s degree in chemistry to fully understand.

Don’t worry! It does not require a vast knowledge of chemistry to create a working feeding regimen and a productive indoor garden.

Generally, growers with a basic understanding of their fertilizer’s contents, and the willingness to experiment, make the most successful indoor gardeners.