Just like vitamin and mineral deficiencies can cause issues like anemia and scurvy in humans, a lack of essential nutrients will lead to issues with plants. Sometimes, the soil provides all the nutrients a plant needs-just think about towering trees and vibrant wildflowers growing in lush forests. However, gardeners often need to supplement the soil to keep their vegetables and flowers healthy.
However, choosing the correct type of fertilizer isn't always easy. After all, there are hundreds of different products, and plants can't speak to tell you what they need. Understanding the various plant nutrients and the different types of amendments will help you learn how to apply the correct products. This easy fertilizer guide has all the answers you need for a thriving garden!
What Are Fertilizers?
Fertilizers are substances added to the soil to supply nutrients and improve plant growth. They can be made from naturally occurring materials like manure, bones, and alfalfa, or from substances synthesized in a laboratory.
Sometimes, the soil contains enough minerals to supply plants with what they need. Other times, the soil lacks plant-available nutrients, and gardens benefit from the addition of amendments.
What Nutrients Do They Supply?
As you've read above, the goal of fertilizers is to supply plants with nutrients. However, not all fertilizers contain the same types or amounts. That's because different species have varied nutrient needs, and soils differ in nutrient composition. Therefore, your goal is to add a fertilizer that only supplies your garden with the nutrients it lacks.
When you look at fertilizers, you may see any of the 15 essential plant nutrients listed on the label. Although plants require 18 nutrients, they obtain carbon, oxygen, and hydrogen from air and water.
Looking at the nutrients present and the amount of each nutrient will help you choose a fertilizer that's right for your garden. Understanding the role of each one makes it all make sense. With that said, here are the nutrients you can look for on fertilizer labels.
Macronutrients
All fertilizers contain a label displaying the NPK ratio as three numbers separated by dashes.
Plants require large amounts of the three macronutrients: nitrogen (N), phosphorus (P), and potassium (K). That's why all fertilizers contain a label displaying the NPK ratio as three numbers separated by dashes. These numbers show the percent by weight of the three macronutrients.
For example, a fertilizer with an NPK ratio of 12-6-10 contains 12% nitrogen, 6% phosphorus, and 12% potassium. It's also possible that a fertilizer may display 0-0-0 when it lacks macronutrients but contains other elements plants need.
Nitrogen (N)
One of the most important elements, nitrogen is necessary for protein formation, chlorophyll production, DNA transfer, enzyme formation, and more. Plants require nitrogen throughout their lives, so you should aim to supply them with a continuous supply of this nutrient. Since this element readily moves throughout the environment via the nitrogen cycle, the amount of nitrogen present in the soil varies from one week to the next.
It's important to recognize that nitrogen takes multiple forms, and not all of them are available for plant uptake. Many sources of organic nitrogen must be broken down by bacteria before the nutrient is available to plants. Therefore, you should aim to foster a healthy soil microbiome whenever you apply organic nitrogen fertilizers.
Phosphorus (P)
This macronutrient helps plants form cells, transfer energy, and synthesize proteins. It's a main constituent of the energy transfer molecules adenosine diphosphate (ADP) and adenosine triphosphate (ATP), which send energy throughout the plant to complete processes like photosynthesis, respiration, and cell division.
Potassium (K)
Although it's not a structural component of plant compounds, potassium plays a crucial role within plants. It helps with water movement, thereby maintaining turgor pressure within cells and helping plants deal with drought stress. It also plays a key role in moving nutrients and sugars throughout the plant and activating enzymes. When you put all this together, you'll find that potassium helps improve both pest and disease resistance.
Secondary Nutrients
Plants require the three secondary nutrients in moderate amounts. Although they won't be listed on the fertilizer's NPK ratio, you can look for the percentage of each nutrient on the label.
Magnesium (Mg)
Each chlorophyll molecule contains a magnesium atom in its core. Therefore, magnesium is essential to photosynthesis. Magnesium also helps with cell division, response to temperature and light, fat formation, and enzyme activation.
Sulfur (S)
Sulfur is a component of a handful of amino acids that are used to build structural proteins and enzymes. It also helps plants form fats and starches.
Calcium (Ca)
This element is an important component of plant cell wells. It also moves compounds through cell membranes. Calcium availability depends on water concentration, so calcium deficiency in crops is often caused by insufficient or inconsistent irrigation rather than a lack of calcium in the soil.
Micronutrients
Although plants require only small amounts of the following elements, they're still essential to plant growth. Sometimes, a sufficient amount already exists in the soil, but if they don't, you should supplement the soil with an appropriate mineral amendment.
Manganese (Mn)
Manganese helps activate enzymes that drive processes like photosynthesis, pollen formation, and nitrogen metabolism.
Iron (Fe)
Iron is involved in many plant processes, including chlorophyll production and cellular respiration. High pH inhibits plant availability of iron, so it's possible for soils to be high in iron while plants remain iron deficient.
Chloride (Cl)
Chloride is needed for photosynthesis and enzyme activation. This element also helps regulate water uptake in soils with high salt levels.
Zinc (Zn)
Zinc is a component of multiple enzymes, including those that break down proteins and transfer energy via oxidation. It also helps with starch formation, seed production, and the production of growth hormones.
Types of Fertilizers
While all fertilizers supply nutrients, you can find hundreds of different types of these products! There are multiple ways to classify fertilizers, including whether they are synthetic or organic, liquid or granular, and quick-release or slow-release. I'll cover a few of the different categorizations to help clear up fertilizer labels.
How Do You Determine Which Product to Apply?
A soil test is the best way to determine which nutrients your soil lacks. All you have to do is take a few samples of the top six inches of your garden's soil and send them to a lab. The soil scientists will run a series of chemical reactions and tell you what is present in the soil, as well as factors like soil pH and the percent of organic matter.
Once you have the test results, you can determine which products to add.. In addition to paying attention to deficient nutrients, you should also note those present in excess. When you choose a product, avoid picking one that contains the nutrients already present in excess.
It's also important to look at the pH. Soil pH has a big impact on nutrient availability. If the pH is above 7.0 or below 6.0, some nutrients will be unavailable to crops even if they're in the soil.
With pH and excessive nutrients in mind, you can pick your product. One option is to apply multiple fertilizers that contain a single nutrient. For example, if your soil lacks nitrogen and potassium, you can add blood meal and langbeinite. Or, you can add a product that contains both nutrients, like fish fertilizer or a fertilizer blend.
