There are three main numbers indicated on a fertilizer label. Those three numbers are reflected as X-Y-Z and are meant to help you decide which fertilizer to use.
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How to Read a Fertilizer Label
In the example above, the three main numbers on the fertilizer label are 5-1-1. Those three numbers represent the percentage of N-P-K that are included in the bag, per bag weight. (N stands for Nitrogen, P stands for Phosphorous and K stands for Potassium.) These are always the three main numbers located on the fertilizer bag/container. Any other essential plant nutrients that are found in the fertilizer are also required to be labeled on the packaging.
There are 17 essential plant nutrients, which means that those 17 nutrients are required for successful plant growth. When those are further broken down, there are macronutrients (those needed in large amounts) and micronutrients (those required in trace amounts). Nitrogen, Phosphorous and Potassium are all macronutrients and are all required in large amounts. When the plant is not receiving these elements naturally, a fertilizer should be considered.
What is a Fertilizer?
A substance is classified as a fertilizer when it can be applied to the soil or plant material and provide essential plant nutrients directly to the plant. When fertilizer is applied to the soil, it is absorbed by the plant roots during irrigation or rain events. In the case of applying fertilizers to plant leaves (foliar), the leaves absorb the nutrients, although not in as great of an amount as if they were applied to the soil.
How to Classify Different Fertilizers
Within the category of a fertilizer, it can be further broken down to:
- Complete Fertilizer – A fertilizer that contains some amount of N, P and K (e.g., 9-14-9).
- Incomplete Fertilizer – A fertilizer that does not contain all three of the primary macronutrients (e.g., 0-10-10). This means that the fertilizer can contain either one or two of the primary macronutrients (N, P or K).
- Commercial Fertilizer – A fertilizer that contains at least 5% of one of the N, P, K elements (e.g., 5-1-1).
- Specialty Fertilizer – A fertilizer that contains less than 5% of any of the N, P, K elements (e.g., 0.15-0.85-0.55).
How to Read a Fertilizer Label – Real World Examples
Using the example of 5-1-1, if this were a 100 pound bag, there would be 5 pounds of Nitrogen (N), 1 pound of Phosphorous (P), and 1 pound of Potassium (K).
If you are dealing with fertilizer weights that are not 100 pound bags, you will need to do a little math to determine how much N-P-K is located inside your bag. For example, in the container above, it is a 0-10-10 fertilizer in a container that weighs 9.5 pounds, so you would calculate the amounts as follows:
- N = (0) x 9.5 pounds = 0 pounds Nitrogen
- P = (0.10) x 9.5 pounds = 0.95 pounds of Phosphorous
- K = (0.10) x 9.5 pounds = 0.95 pounds of Potassium
How to Determine What Fertilizer is Needed
Determining nutrient deficiencies in plants is not as easy as one may think. When determining which element your plant is deficient in, you should:
- Do some research based on the type of plant that you have
- Compare your problematic plant to what the plant should look like (a control plant)
- Check to see if there are any other issues besides nutrient deficiencies (e.g., pest issues, over/under watering, etc.)
- Then start looking into what deficiencies you are dealing with
A helpful guide to determine generic plant deficiencies (not specific to certain types of plants) can be found through the University of Arizona Extension.
How to Choose which Fertilizer to Use
Once you determine the element(s) in which your plant is deficient, you need to select the proper fertilizer. In regards to the three primary macronutrients (N, P and K) that are noted on the fertilizer label, it is important to know which one your plant is lacking, so that you only fertilize for what is needed. It is not common for plants to be deficient in all three, so you want to plan accordingly to make sure you are addressing the plant’s needs, but not overfertilizing. For example, if your plant is only deficient in Nitrogen, you would want to look for a fertilizer that had Nitrogen and had none or very little Phosphorous and Potassium.
How to Fertilize
There are multiple methods used to fertilize, but we will only review four of them.
- Broadcasting – This method can be used with both liquid and dry fertilizer, and is where the fertilizer is applied above the soil surface in some sort of uniform manner. I am sure you have seen your parent, spouse or neighbor using this method with a spinning-type spreader.
- Band Placement – This method can be used with dry fertilizer, and is where the fertilizer is applied beneath the soil surface (subsurface), either beneath the seeds/established plants or several inches to the side of the seeds/established plant root ball.
- Sidedressing – This method can be used with dry fertilizer, and is where a trench is created between plant rows, dry fertilizer is applied and covered up and once there is irrigation and/or rain, the nutrients from the fertilizer flow to the plant roots that grow out into the rows.
- Foliar Applications – This method can be used with liquid fertilizer, and is where the fertilizer is directly applied to the leaves. This is not a common method and if used, it needs to be done in conjunction with another fertilizer application type as not enough nutrients get absorbed by the foliar material (plants). If used, these are commonly used to apply micronutrients, but can also be used to apply Nitrogen in the fall (if in the middle of summer, the leaves will fall off) and Potassium.
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