Do you ever have nightmares about being stuck in a long, dimly lit aisle at the garden store? You’re looking at all the bags of fertilizer with blank uncertainty. What do those fertilizer numbers mean? Should they all be equal, or should one number be larger? Will this bag kill my garden, or save it?
I’ve had that nightmare, and I’ve lived it. After all, walking down those aisles can be intimidating. The bags are rarely self-explanatory, and there are usually six or seven other customers clamoring for an employee to decode the labels. But don’t worry, in a few minutes, you’ll be the expert. No more nightmares!
You’ll always see three numbers on a fertilizer bag. Each number refers to a certain nutrient, and tells you how much of that nutrient is in the mix.
The fertilizer numbers represent a percentage of the mix, but don’t worry: they’re not supposed to add up to 100%. Most of the fertilizer is made up of a base, a small host of minerals and vitamins, and those three numbers. Sand, water, or other natural materials make up the base in many fertilizers. Which is good: you’re buying a balanced product.
The three-number label on fertilizer refers to the amounts of Nitrogen, Phosphorus, and Potassium in the mix. They are always in that order. These nutrients are called the “macro-nutrients because they are the three major elements that plants need consistently to thrive.
Fertilizer is considered a “complete fertilizer” when it contains all three of these nutrients. But don’t be confused by that term. Just because a fertilizer is “complete” doesn’t mean that it’s an all-purpose plant food. Some fertilizers are ideal for growing grass or lush lettuces, while others are designed to give you a bumper potato crop.
Everything depends on the balance of nutrients, because each nutrient supports a different area of growth.
The first number is always going to give you the amount of nitrogen in the mix. Nitrogen gives your plants a great boost of leafy green growth. The nitrogen number is often higher than the other two. That’s because nitrogen tends to get depleted quickly.
The second number refers to the amount of phosphorus. This is the nutrient your plants need to produce flowers and fruit. It also promotes strong root growth. Complete fertilizers for vegetable and fruit gardening have higher levels of phosphorus than those developed for growing grass and leafy plants.
Potassium (or Potash)
If you’re wondering why Potassium levels are represented by a K in fertilizer numbers, then you were probably sleeping through chemistry class too. K is the chemical symbol for potassium. It’s from the Latin word Kalium, which means potash. However you choose to refer to it, potassium is there to help your plants stay healthy and fight off diseases.
Ok, got it? Nitrogen, Phosphorus, Potassium; leaves, fruit, immunity. Now that you know what the numbers mean, picking the right fertilizer for your plants is going to be a lot easier.
Let’s take a look your garden now, to get an idea of which nutrients you need to focus on supplementing.
What’s the Trouble?
First, figure out why you’re in the fertilizer aisle to begin with. Are your plants looking a bit peaked? Are your radishes heavy on the greens, but barely producing roots? Or are you just looking for a mild, supportive fertilizer?
Know what you’re looking for before heading to the store. After all, if it’s just a little boost your garden needs, DIY remedies may be the best bet. For steady, consistent feedings, try brewing up a compost tea, or working in some fresh manure from a neighbor’s alpacas.
If you’re addressing a specific problem, however, choose a specific solution. The best way to find out exactly where your trouble spots are is through observation and testing.
My garden surrounds my house in a little, woodland clearing. We have a lot of pine trees, loose soil that packs down easily, and lots of weeds. Pine trees tend to prefer acidic soil, and with so many of them towing around our yard, we can safely assume that our garden soil tends to be slightly acidic as well.
As a result, leafy greens and herbs thrive in our garden, while root crops like radishes and beets are only moderately successful. We often amend our soil with well-composted manures from our chickens, goats, and sheep. All of these manures give a healthy dose of nitrogen, and you can see that in the way the greens thrive.
When I’m looking around for additional supplements for my garden, I want something with a very low N, and higher levels of P and K. Bone meal is a great option for an organic, phosphorus-rich fertilizer. Additionally, kelp meal can boost potassium. While I’m amending the soil, I should look for ways to balance the pH levels and loosen the soil a bit.
Your garden may be showing similar issues, or it may look completely different. Nitrogen is the nutrient our gardens tend to eat up, so look carefully for signs of nitrogen deficiency.
A nitrogen-deficient garden shows poor plant growth, pale green leaves, and stunted, straggly plants. Make sure your garden gets consistent nitrogen support before it reaches deficiency for the best growth.
Putting it All Together
Once you’ve identified your garden’s primary needs, you need to decide which fertilizers will work best. After all, every garden is unique, and each fertilizer blend is unique as well. Sometimes finding the right match for your garden takes a little effort. But it can be a bit of a challenge.
The right fertilizer for you can depend on everything from the quality and texture of your soil to how quickly you want to see results.
Slow-feeding, organic fertilizers are great for long term nourishment, whereas chemical fertilizers act as fast food for your plants. They give quick results, but you need to reapply regularly.
The Trouble with Chemical Fertilizers
In my garden, I only use organic fertilizers. I stay away from chemical, or synthetic fertilizers for a few reasons. Primarily, because while these fertilizers give your plants a quick boost, they also deplete the soil.
Chemical fertilizers destroy the humus in the soil: the living matter in there. It’s this decomposing matter that makes the soil rich, healthy, and able to sustain plant life. Chemical fertilizers actually kill the soil. They make it incapable of growing healthy plants, unless you want to keep buy commercial fertilizers, of course.
Synthetic fertilizers also have to be applied very carefully. Don’t allow the fertilizer to touch your plants directly or it will burn them. In fact, mis-applying chemical fertilizers can actually kill your plants. Even if you’ve chosen the right balance of nutrients, those nutrients are at dangerously high levels until diluted.
So, while you’ll get impressive growth from applying the right synthetic fertilizer in the right way to your plants, it’s not worth the havoc those chemicals will wreak on the soil.
The Organic Option
Organic fertilizers affect the soil in a completely different way. Because they’re made up of organic materials, these fertilizers actually feed the humus in the soil. Unlike the fast food of chemical fertilizers, organic fertilizers produce long-term, sustainable results.
Now, these organic fertilizers don’t have to be certified organic. They’re called organic because they’re made up of living matter—not because they were grown free of pesticides or artificial agents.
For example, my compost bin is full of both certified organic and non-certified organic vegetables. They’re all composting together. The compost tea I make from my bin is an organic fertilizer, because it’s a living fertilizer, but it isn’t a certified organic fertilizer.
Furthermore, these fertilizers don’t have to be the pricey, certified organic options. They can be free manure from a dairy farm or compost from your own backyard. Organic fertilizers use natural sources of nitrogen, phosphorus, and potassium to build up the soil. Your plants get long-term, nutritious meals, and your garden beds improve every year.
Just keep in mind that organic fertilizers act more slowly. Don’t expect to see the instant results you’ll get from chemical fertilizers. This means that you can safely use them more often without burning your plants. There is still a risk of over fertilizing though.
Whether you’re living on McDonald’s cheeseburgers or cooking from scratch every night, over-eating is unhealthy. It’s the same with fertilizers. Over feeding your plants—with chemical or organic fertilizers—will harm them too. Every plant will be overwhelmed by too much fertilizer, even hungry corn stalks. Some plants, like aloe and rosemary, are quickly saturated. Others will eat like teenagers.
Fertilize attentively, and err on the side of under-feeding rather than over-feeding. You can always bulk up the soil later, but adding too much fertilizer can’t be undone.
Know your plants, and pay attention to those fertilizer numbers. Some plants prefer poor soil, others love an abundance of rich soil. Fertilize for individual plants, and work gently. Your garden is your masterpiece, so build it up carefully into a place of beauty and sustenance for you and the world around you.