The Dirt on Fertilizer

For plants to thrive, they require a magic formula: water plus sunlight plus air plus fertilizer. Many green thumbs forget the last part of that equation. But fertilizers—substances that make soil more fertile—are essential to plant health because not all soils are equally nutritious. In short: Fertilizer is plant food. Or, as Oregon State University puts it, “The best way to feed your plants is by building good soil.”

Fertilizer basics

The concept of soil fertilization likely extends back 8,000 years, when early farmers added manure and bones to their crops. Chemical versions weren’t invented until the 19th century, and their widespread use didn’t come about until the second half of the 20th century. Nowadays, fertilizers are an essential part of farming, and there are plenty of options: synthetic or organic (think: manure or seaweed), liquid or dry options, and a wide variety of formulations. 

All plants need fertilization. After sitting in the same soil week after week, they eventually eat up all of the nutrients, which then need to be replenished. Which fertilizer they need, however, requires some sleuthing. 

Most fertilizers are composed of three major nutrients: nitrogen, which stimulates the growth of healthy leaves; phosphorus, which encourages root and flower production; and potassium, which supports general health and disease resistance. (You’ll see these noted on bags of fertilizer as an NPK ratio.) Some fertilizers will also include micronutrients such as iron, copper, zinc, and magnesium. The best way to determine which nutrients your soil is lacking is via a soil test.

For home gardeners: Fertilizers can also be formulated for specific types of plants. There are versions for annuals, vegetables, turf grass, tropical houseplants, etc. Choose—or blend—the one(s) that best fit your greenery.

Fertilizers in agriculture

Of course, fertilizers are especially important when it comes to agriculture, and are responsible for boosting crop yields. Fertilizer application is believed to have been responsible for at least 50 percent increase in crop yield in the 20th century, according to an article published in Agriculture in 2022. Higher crop yields mean that less land is required for agriculture, which can benefit wildlife habitats and forests.

But fertilizer is a delicate addition to farming practices. Use too little and the crops lack critical nutrients. Apply too much, and you can offset the pH of the soil, thwart plant growth, increase pest attacks and cause topsoil erosion, among other issues. 

The use of chemical or synthetic fertilizers can also have serious environmental consequences. Their high concentrations of nitrogen and phosphorus can leach into and contaminate groundwater, cause algae blooms that harm aquatic ecosystems and remove healthy bacteria from the soil. One major example: the Gulf of Mexico Dead Zone, where overwhelming amounts of nutrients such as nitrogen and phosphorus have killed off marine life.   

Animals that eat fertilizer-treated plants can get sick, and some research shows that synthetic fertilizers are causing decreased fetal weight, neurological damage, diabetes, and cancer in humans. 

Globally, only about 35 percent of the nitrogen applied to plants is actually absorbed by them, leaving the rest to run off into the environment. Precision farming can help growers use fertilizers more efficiently so they get more of the benefits and less negative side effects.

It pays to be stringent about fertilizer use, not just for the health of the planet, but for the health of your wallet. Drastic jumps in fertilizer costs are hurting farmers’ bottom lines. The USDA forecasted that input costs for the 2024 growing season are expected to hit the third-highest level in history. Though fertilizer costs are expected to drop from their all-time high, the category remains a significant expense; for example, fertilizer accounts the largest single operating cost when growing corn. In short: Being smart about where fertilizer is applied, and how much, can have a major impact on budgets. 

Using fertilizer 

Adding fertilizer when a plant is in its dormant cycle can mess up its natural cycles. You’ll get the most out of fertilization at the start of spring when plants are generally in their active growth period. Depending on the plant, additional applications (every couple of weeks or so) may follow until fall; some indoor greenery also benefits from sporadic applications throughout the winter. 

As we’ve mentioned, just be cautious about how much you use—too much can have a contradictory effect, damaging the plants and the environment. 

Thankfully, there are safer alternatives available. 

Organic fertilizers are considered healthier for the environment and for us because they are made from living organisms (like fish emulsion). Two challenges that come with these options: They can be pricier, and they’re slow-release, meaning it’ll take days or weeks for the effects to become evident. 

Outside of the home, additional organic materials—like grass clippings, cover crops, or compost—can also help support soil health, suppress weed growth, and reduce soil erosion.

What do you want to know about fertilizer? Ask a question in the comments section below.