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Fertilizer is, unfortunately, a topic that can paralyze many gardeners.
To be fair, plant nutrition and how plants “eat” is very mysterious. Most gardeners don’t understand it well, which leads to not being confident in their fertilizer choices.
Fortunately, we have many decades of experience using fertilizers and practicing general plant nutrition. So, we can perhaps shed some light on the subject.
This article is going to explore plant nutrition and the various details around both the organic process and plant fertilizers. By the end, hopefully you’ll be more confident in your choices!
Our goal here is not to pick a fertilizer for you. Rather, to inform you of the options and decisions the grower has to make and why you might choose one or another.
Our hope is to get you to the place where we sit. Knowing that all the products out there will do the job, but your specific preferences might guide you to a particular decision.
First, What Do Plants Actually “Eat?”
Most gardeners understand the basics of plant nutrition. Most growers know the “big three,” often referred to as NPK. These stand for nitrogen, phosphorus and potassium.
But, it goes quite a bit deeper than that.
To help us define and categorize these nutrients, two classifications are used. These are called macronutrients and micronutrients.
There are several ways to define these two classifications. The simplest way to think of it is that macronutrients are consumed in the greatest quantities, whereas micronutrients are consumed in much lower quantities.
There are several macronutrients that are consumed by a plant, which are responsible for the bulk of the plant’s health:
- Nitrogen
- Phosphorus
- Potassium
- Calcium
- Sulfur
- Magnesium
- Carbon
- Hydrogen
- Oxygen
In the micronutrient category, plants need small amounts of these things to maintain optimal health:
- Iron
- Boron
- Chlorine
- Manganese
- Zinc
- Copper
- Molybdenum
- Nickel
All told, that’s 17 macro and micro nutrients that a plant needs to maintain optimal health.
Some of these elements can come from the soil, especially the micronutrients. Others must be supplemented by the gardener, to meet the needs of the plant.
Why Must The Gardener Fertilize Their Plants?
To understand this, let’s first consider how plant nutrition works in the natural world. Obviously, there aren’t fertilization fairies flying around.
In a prairie or a field, grasses and perhaps some small flowers, grow in the field over the summer months. In winter, these plants die off and become fodder for natural organic composting processes. This compost then results in new NPK for the next season’s prairie or field.
Or, let’s consider the forest. The tree’s leaves, needles or branches fall to the ground, ending up in an identical decomposition process that supports the forest floor and all trees, plants, mushrooms and flowers within that forest.
Both of these are “closed loops.” The amount of NPK the prairie or forest creates determines (or limits) the growth of plants that can be supported in that environment.
Should the soil become more rich in nutrition, the area can support more life. If it becomes more lean in nutrition, some plants may not survive. Nature always finds the balance.
The garden, however, is very different from this natural example.
In the garden, we intentionally sow or transplant plants into the soil. We then harvest most of that plant (crop) out of the soil. With the intention of using its nutrition to support our own nutritional requirements.
There is very little “natural decomposition” that occurs in the garden. It is inherently unnatural, at least when compared to nature.
But, those same nutritional limits that apply to the soil in natural environments also apply to the garden. In addition, the gardener is constantly reducing the available nutrition.
Since the “closed loop” doesn’t happen in the garden, the grower must supplement by adding to the nutritional profile of the soil to reach the needed balance.
How Do Plants Actually Eat?
We will avoid the very complex biological and biochemical processes involved with answering this question. We need to keep this topic in the stratosphere.
To simplify this answer, it’s important to see plants (and the entire natural world) as masters of chemistry. It’s also important to understand that chemistry is a natural process, not a man-made one.
It’s also helpful to have a non-anthropomorphic understanding of plants. They don’t have little teeth on their roots, chomping away at stuff in the soil.
If you’ve had a basic exposure to chemistry, you probably recognized the previously mentioned macro and micro nutrient lists as chemicals.
Or, perhaps you thought of them as elements from the periodic table of elements, also known as element chemicals.
These chemicals occur all throughout organic life. From the grass leaf to the common rock; the fallen branch to the statured moose.
The gist is that plants and soil microbes are experts in this chemistry. As such, they are responsible for breaking down more complex chemicals and chains into simpler ones that plants can use.
They use biological processes such as interconversion and assimilation to convert one chemical to another. This continues until the original thing becomes useful to a plant.
A couple brief examples? Rock phosphate can become calcium, phosphorus and other things. The nitrogen in a tree leaf can become ammonium, nitrite, nitrate, nitric oxide or nitrous oxide.
In the examples above, it’s not the rock or the tree leaf providing nutrition to the plant. Rather, it’s the complex web of chemistry masters (plants and microbes) at work.
We call this the organic process.
Once these microbes and plants have done their chemistry work, these simpler chemicals can then be absorbed and used by the plant through its roots.
You could “sort of” think of this like drinking, but there’s many chemistry based tricks involved in how plants actually absorb nutrition. For the purposes of this article, though, let’s go with the drinking analogy.
Do Plants Eat Compost? How Does That Work?
In a word, no.
We described the basics of the organic process above. Compost, or decomposed material, is one stage of that organic process.
However, it’s important to understand that the original organics and compost are not the only two possible states.
Compost must be further broken down, by the plants and those soil microbes into basic chemicals that are usable by the plant.
An example is the compost may have ammonium in it. That’s worthless to the plant. First, soil microbes must convert it to usable chemicals like nitrite or nitrate.
In the context of a bag or pile of compost, this process is happening at all sorts of different levels at any given point in time. Some is unprocessed, some is partially processed and some are the final chemicals that are immediately available to plants.
So, to complete the thought, compost is sort of the natural “crafting ground” of plant nutrition. But, by itself, compost is not the actual food the plant uses.
That said, compost can provide plant nutrition. In subarctic gardening, we experience a much slower organic process than is seen at lower latitudes.
This makes using compost alone a more difficult venture. It’s not impossible, but will be less performant than fertilizer based practices.
What’s A Fertilizer? How Is That Different From Compost?
Up to this point, we’ve largely discussed the organic process. This is how nature, and indeed many gardeners, feed their plants.
However, humans are quite smart. We’ve come to understand the organic process and chemistry well enough that we can intentionally involve ourselves in these processes.
Various chemistry practices can be used to both convert complex chemicals or outright synthesize various chemical forms. We can also isolate chemicals in some of their purest possible forms.
By that, I mean – the stuff plants actually use. Nitrogen, potassium, phosphorus and so on.
Sometimes that fertilizer is “slightly” more complex version of these chemicals, most often seen in organic fertilizers. But, the goal of a fertilizer is to be comprised of something very easy for microbes or plants to convert into real plant nutrition.
For the most part, whether we’re discussing organic or inorganic fertilizers, this same general goal is present. To provide simple chemical compounds that plants can very readily use.
The notable difference to the organic process is that fertilizers undergo some form of industrialized process. This is true regardless of whether we’re discussing organic or inorganic fertilizers.
The Real Difference Between Organic and Inorganic Fertilizers
We have some strong opinions on this topic. We’ll also tell you that there is a ton of misinformation out there. A lot of where people stand comes down to what only be described as “belief.”
As we stated above, both organic and inorganic fertilizers undergo some form of industrialized process. So, that’s not the distinction.
Furthermore, both organic and inorganic fertilizers are often comprised of (or sourced from) the exact same initial ingredients. The logical place to harvest the chemicals needed for life is the very world where they come from. Plants, rocks and sometimes animals. So, that’s also not the answer.
Where the distinction really comes in is how far the industrialized refinement process goes.
Organic fertilizers will usually feature the desired chemical(s), but with one or more carbon elements attached to it. Whereas inorganic fertilizers will not have that carbon element.
Here’s the thing, though. Perhaps surprisingly, plants don’t utilize organic chemicals. First, microbes or roots must break that carbon off. Essentially, turning that chemical into an inorganic one.
When we get into the stuff plants actually use, we’re exclusively talking about inorganic chemicals. There is no such thing as an organic and an inorganic nitrate, for example.
The informed organic argument is about that carbon. It’s essential for life, indeed it’s one of the major macronutrients!
But, to assume that a grower using inorganic fertilizers doesn’t “get it” or care about that carbon is more an opinion as opposed to a fact. There are countless ways to add carbon into the garden. Fertilizer is just one of them.
This discussion is so tribal anymore that it now defies basic logic. The tribes that beat the organic drum are also commonly the tribes that argue we should reduce our carbon footprint.
This tribalism often runs counter to scientific study. Claims such as “synthetic fertilizers destroy soil habitats” are regularly proven false. It’s at the point now where it’s an argument and the facts were lost long ago.
The truth is this. There is not a “correct” way and both methods work.
If you use organics, your plants and soil microbes will simply turn it into inorganic fertilizer, whether you like it or not.
What Are Complete Or Blended Fertilizers?
Complete fertilizers (sometimes called blended fertilizers) are designed to provide plants with the overwhelming majority of the macro and micro nutrients your plants need.
In complete fertilizers, many things are “blended” together to create a more comprehensive plant fertilizer.
This is, frankly, most fertilizers out there on the market.
The exact composition of the fertilizer will vary from brand to brand. But, the product will functionally provide the major nutrition that a plant needs.
Now, there are different philosophies that go into the design of a fertilizer. Some manufacturers (or specific product lines) assume that plants can get some of their nutrition from the soil itself. Examples might be for things like calcium or copper, both commonly found in natural soils.
In many ways, this is a correct view. With many of the micronutrients, especially, they are naturally occurring and needed in such low quantity it doesn’t make sense to provide it in a fertilizer.
Some fertilizers, however, are “more complete” than others.
An example of where you’ll see “more completeness” are with tomato focused fertilizers. These typically provide larger amounts of calcium and magnesium, since tomatoes need these in higher quantities than most other plants.
An interesting thing about hydroponic fertilizers is that they, by necessity, must be complete. Although we’re focusing on soil growing here, hydroponic nutrients are interesting because they cannot rely on nutrients in the soil.
Many hydroponic fertilizers can be utilized in the soil gardening space. Marketing and potential use are two different things.
In fact, as we’ve navigated this topic, we’ve heavily favored this strategy. It eliminates concerns of invisible nutritional deficiencies, especially with crafted soils or incomplete organic processes like we see in the north.
Generally speaking, unless you’re well experienced with plant nutrition, we recommend most gardeners use complete fertilizers.
What Are Single Ingredient Fertilizers?
Above, we briefly talked about how fertilizers are derived. Typically, they are made from naturally occurring things.
Well, these things can also be used as a fertilizer.
There are many examples of these “single ingredient” fertilizers. You’ve likely encountered them as things like blood meal, bone meal, alfalfa meal, fish meal or oyster shells. There are dozens of these things on the market.
It’s important to understand that the concept of “single ingredient” doesn’t mean “single nutrient.” Many single ingredients provide multiple macro or micro nutrients.
It’s also important to understand that no one “single ingredient” fertilizer is a complete fertilizer. They must be combined to develop comprehensive plant nutrition.
Overall, the use of single ingredient fertilizers tends to be a much more advanced approach to plant nutrition. It usually involves knowing what your soil is deficient in and addressing specific nutritional challenges.
The reason for this is because those single ingredients are usually dominated by a particular macronutrient. For example, blood meal is mostly nitrogen. Bone meal is mostly phosphorus. Langbeinite is mostly potassium.
In theory, the gardener can blend these different single ingredients to make a complete fertilizer. However, this topic is much more advanced and not within the scope of this article.
What Plants Need Vs. What Fertilizer Provides
It is essential to understand that the amount of a given nutrient a plant has access to has no bearing on whether the plant will actually use that nutrition.
To anthropomorphize this concept, imagine a massive buffet dinner with hundreds of food plates. The quantity of food doesn’t determine your appetite.
Nutrients certainly have their “special purpose” for the plant. For example, we largely associate nitrogen with leafy plant growth. Or phosphorus with plant vigor.
Simply giving your plants more of something won’t necessarily result in the plant using more of it. This also means we can’t influence the plant’s growth with the nutrition we choose to give it. Plants are gonna plant.
The general goal of plant nutrition is to provide the plant what it needs, when it needs it. These needs also change throughout the plant’s lifecycle, maturity and stages of growth.
Despite this constantly changing landscape, there is no real need for the grower to tailor the nutrition to these stages of growth. In fact, there is no way to “truly know” what your plant needs or when it needs it.
In our opinion, this is one of the reasons that complete fertilizers are more useful to the grower. If the gardener gets the “single ingredient” ratios wrong, the plant doesn’t have what it needs.
Excess nutrition is not harmful to the environment. Over time, it will wash deeper and deeper into the earth, combining with all the other chemistry that comprises the earth and soil.
That’s not to say that too much nutrition is inherently good! Plants can experience fertilizer burn, which is why it’s appropriate to use fertilizers in the way and quantity the manufacturer specifies.
Also, younger plants feed less whereas more mature plants feed more.
Understanding Fertilizer Ratios & Labels
Almost all of the fertilizers will feature a stated ratio. It might look something like 20-20-20, or maybe 5-15-12.
These numbers are telling you the percentage of nitrogen, phosphorus and potassium (NPK) in that fertilizer.
Specifically, if you had a 100 pounds of that fertilizer, you’d have that many pounds of nitrogen, phosphorus and/or potassium. Here’s a couple examples, each at 100 pounds:
- 20-20-20: 20lbs nitrogen, 20lbs phosphorus, 20lbs potassium
- 5-15-12: 5lbs nitrogen, 15lbs phosphorus, 12lbs potassium
- These examples can be converted to different quantities in metric quite easily. Freedom units will require you to do the math.
You might note these numbers never add up to 100%. Fertilizers always have what is called “filler,” typically designed to assist nutritional delivery or other purposes.
What these ratios are generally describing is the relative strength of that fertilizer. It’s also illustrating the comparative strength of the actual NPK.
However, actual strength in the soil is also dependent on dosage rates. For example, one tablespoon of 20-20-20 is essentially equivalent to two tablespoons of 10-10-10.
Our general advice for a complete fertilizer is one that feature a “relative” balance of these three numbers. That doesn’t mean they have to be exactly identical, like 10-10-10.
A good “general guideline” for an all purpose fertilizer is that no one number should be more than half or double the other numbers. Again, that’s a guideline and not a rule.
This approach will ensure sufficient quantities of NPK in your soil.
Water Soluble vs. Granular Fertilizers
For a very long time, growers only had access to granular fertilizers. If you wanted to fertilize your garden, there wasn’t a choice.
Granular fertilizers are aptly named, typically manufactured as pellets, small balls or sometimes chunks or flakes. The exact design comes down to the manufacturing process.
These granular fertilizers entirely rely on water combining with the granules, dissolving and distributing the fertilizer into the soil.
These granular fertilizers are often good for what are called broadcast applications. Essentially, covering large areas of soil with fertilizer.
However, in recent decades, water soluble fertilizers have become available to modern growers. Water soluble fertilizers have quickly become very popular these days as they have significant advantages
These are also aptly named as they are soluble in water, which means the grower can “pre-dissolve” the fertilizer into water.
They are incredibly efficient because they are both immediately available and more easily distribute into the soil. The dissolving step is entirely skipped.
Water soluble fertilizers can easily be applied using watering cans. In larger gardens, it may be helpful to utilize fertilizer injectors or a hose end sprayer like you see in the image above.
In addition, fertilizing your plants once they are in the ground is much easier. Water soluble quickly gets to the plant’s root zone, right where it needs it. No rain or watering required!
In most cases, water soluble fertilizers tend to be slightly more expensive than their granular counterparts. But, that additional cost also translates to performance benefits that aid the northern grower.
Long-Release & Short Release Fertilizers
In the granular fertilizer space, you might come across concepts like “slow release” or “fast acting.”
Essentially, what’s going on here is how resistant the fertilizer is to being dissolved by water. Manufacturers can use different processes to speed up or slow down the delivery of fertilizer into the soil.
A slow release fertilizer is often considered good as a pre-season fertilizer. It will slowly release nutrients into the soil over the growing season, usually aiming to last weeks or months.
A quick release fertilizer will provide more immediate nutrition to your plants. The faster the fertilizer dissolves into the soil, the sooner your plants gain access to the NPK.
Tying in the water soluble discussion above, water soluble fertilizers are the “fastest acting” fertilizers on the market today. Even compared to so-called quick release granular fertilizers.
Much of this comes down to the gardener’s philosophy and preferences. But, you should also consider your plants.
With a slow release fertilizer, you run the risk of your plants needing a particular nutrient, but it has not yet been dissolved in sufficient quantities.
Quick release fertilizers usually feature more frequent application rates, requiring more of your time. These more frequent applications help ensure continual access to NPK.
Personally speaking, as far northern growers, we prioritize growth and performance over ease of use. So, our general preference lies towards quick release (and more specifically, water soluble) fertilizers.
We also use slower release fertilizers, too. Some of our gardens focus on “low feed” crops and thus are more compatible with slow release.
The Value Proposition Is Appropriate
One of the things we’ll stress here is that any fertilizer, from any brand, is going to address your plants nutritional needs.
No matter how you get there, it all boils down to those 17 chemical elements that your plants need.
There are minor differences in how things are manufactured or marketed. More importantly, there’s things like business ethics or ecological philosophy that might matter to the grower.
It’s OK to have preferences!
But, a vein that runs through most of us is value. We all want bang for the buck.
In our experience with fertilizers, the most competitive value in fertilizer are those aimed at commercial and industrial agriculture.
If you ask what a professional grower uses, they aren’t likely to tell you some obscure fertilizer brand or a niche product. They also aren’t likely to use something like Miracle Grow.
Rather, it will be something they can buy in bulk. Usually, 25 pound bags, massive iso-totes or by the pallet load.
In our large scale gardens, we’ve found this to be good advice. We work primarily with manufacturers that are aiming at commercial agriculture, not the retail space.
Yes, this means we often have to buy large quantities. But, we’re going to use it anyway. Fertilizer can last for many years when properly stored.
Some of these manufacturers do pander to the small home grower or niche market grower. They’ll produce smaller quantities, tacking on steep profit for your convenience and budgetary concerns.
More Could Be Said, But Not Today
Hopefully this article has helped you understand the choices, strategies and preferences a grower might have when it comes to picking a fertilizer.
We will again tell you that there is no singular “correct” fertilizer to use on your gardens.
There’s more that goes into the discussion, too. For example, in our recent soil pH studies, the choice of fertilizer can have a huge impact on the grower’s garden.
But, as with most complicated things, it’s usually best to focus on the basics and get down to the truth.
As always, if you have any thoughts, comments or if you want to rage against our opinions on organics…there’s a comment box down below!
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