All the Uncomfortable Facts about Fertilizer

Fertilizer Basics: What it is and how it is made.

“Fertilizing” was discovered early in human history. Simple observations by early humans would have found some plants grow better “here than there,” or that plants grow best in the first year in a new spot. Therefore the addition of raw materials, like manure, to enhance farm production began very early on. Much later in history examination into the chemistry of fertilizers lead to discoveries in what plants need and other ways the produce fertilizers from raw materials.

Just like then, much of our fertilizers come from naturally occurring raw materials. Potash is mined for potassium, and phosphorus and other minterals are dissolved from rocks. Nitrogen (sometimes the largest component in fertilizers) is usually chemically synthesized using urea and ammonia and acids.

Essentially, chemical fertilizers (of reputable sources), are not far off their natural equivalent, except in how they are processed and purified – usually to make them less expensive and save on shipping costs.

Fortunately, after WWI, the factories turning nitrates into explosives quickly changed to pump out fertilizers and it has become a massive industry. It is believed that within the next 50 years we will have a food crisis where our existing methods of food production will need to shift to accommodate greater needs on less land. Fertilizers have helped us produce more food per square foot thus far, but we may depend on it further.

How it works: chemical basics, which to buy

A typical fertilizer is described as a three-part number indicating the percentage of each primary nutrient. For example, a 12-10-5 fertilizer contains 12% Nitrogen, 10% Phosphorus and 5% potassium by weight. These numbers are in a standard order always listing Nitrogen (N) – Phorphorus (P) -Potassium (K) in that order.

Generally, different plants have different needs and at different times. For example, leafy vegetative growth often uses lots of Nitrogen. To firm-up the stems, potassium is required. And sometimes flowers are enhanced with available phosphorus. Not all fertilizers are interchangeable, however. Some plants need an acidic formulation, and some can be easily over-fertilized. The three-part ingredient label is supposed to be used to determine how much volume of a fertilizer you need to get the desired amount. For example, if you need 1kg of Nitrogen in a garden bed then you’d need 5kg of 20-20-20 to achieve that. And if that was the right amount of Nitrogen, but twice as much of the others as you’d need, you’d opt for a 20-10-10 fertilizer.

This highly productive raspberry bed is entirely natural clay soil with a bit of horse manure added to the surface three years previously.

What this numerical identification does not help with is how quickly it is absorbed. Typically, a chemical fertilizer is absorbed immediately. This is great to rectify a problem, but requires you to reapply. Organic fertilizers still need to break down naturally, which has many benefits to your soil including enhancing microbials, but they can release as quickly as in a week or as long as several years depending on the material.

If you get nothing else from this, know that the more refined a fertilizer is the quicker it is absorbed.

Environmental considerations: limited resource, run-off.

The major critique of chemical fertilizers is that only some of it is absorbed by plants and it is easy to over-do it. Too much fertilizer is a major environmental concern as nitrates (a concern for human health) end up in our drinking water and we have the unfortunate ability ability to change salinity or nutrient load in bodies of water we depend upon.

Another concern is that much of our inexpensive resources for fertilizers are limited. Mines that produce the raw materials will eventually run out, and we’ll be kicking ourselves for refining it so well that it all ended up in the ocean.

If you have environmental concerns but want to fertilize, consider using commercial fertilizers as plant medicine, but organic fertilizers (like compost) as your annual contribution to your soil.

One exception is ocean-based fertilizers. I want to plead to you not to take seaweed from the beach or buy seaweed based fertilizers. At the rate we are changing our oceans this is not a renewable resource and there isn’t enough to go around, even now. It is often a favourite of home growers because it is absorbed quickly, just like refined fertilizers.

potted plants almost always need fertilizers unless grown with actual soil. Even then, moisture control is important for nutrient uptake despite what is available in the media.

Plant interactions: Nitrogen, P and K and how plants react.

The fertilizer industry is important. For home growers, it’s a bit of a racket. We know what some nutritional deficiencies look like and we can correct them with fertilizers. For example, yellowing leaves are often a nitrogen deficiency, so add more N. Or spotted yellow leaves is a potassium issue, so add more K. However, what they don’t tell you is that most deficiencies are caused by fertilizing in the first place: If you grow a plant in rich soil or with chemical fertilizers it will grow according to what is available. Should the nutrients run out the leaves will yellow because it isn’t getting the N needed to support the growth it created. Alternatively, if you grow a plant in poor soil, it might be smaller, but the leaves won’t go yellow, since it tried to grow with what was available. Of course, this changes from plant to plant and soil to soil, but my point is: fertilizers are sold like a drug – once you start, you can’t stop. And what is seldom asked is “do my plants actually need to be bigger/greener..etc”. If you’re desperate for fast growth and grocery store looking produce then you will need to fertilize aggressively. And that comes at a cost.

Secondary interactions: plant and compost pests and flavour compounds

Another seldom talked about issue is that plants don’t always want to grow as fast as we can make them with fertilizers. Sure, we associate vibrant green leaves with plant health, but our plants don’t always see it that way. Lots of nitrogen produces dark green, new growth. But that growth is soft and is very attractive to pests. Commercial growers know that fertilizers attract sucking insects like spider mites, whitefly and aphids. Too much fertilizer and you are literally feeding the bugs more than the plants. And this is easier for bugs to discover than you think. They can see different wavelengths and plants put off different wavelengths according to stress and fertilizer levels. So if you over fertilize one plant, they will find it.

Furthermore, rapid growth sometimes is attributed only to the main N,P,K nutrients. That growth rate does not allow the plant to build up other compounds – some of which are flavour related. Yes, you can fertilize grapes and make them huge, but side by side, a fertilized grape and a non-fertilized grape will have the same amount of sugars and flavour compounds, and only water content makes up the difference in size. This shouldn’t be a far-fetched notion, as I bet you’ll admit no carrot tastes better than a small organic one.

In summary, be careful when you push your plants.

The rude, crude industry and a gullible market.

As mentioned, the fertilizer industry is a bit of a racket. And I don’t mean the major producers, I mean the companies bagging them for home use. If you take any major horticultural-grade fertilizer company you will find that their products include a wide range of N,P,K ratios with different micro-nutrient options (sulphur, choline, magnesium, copper..etc.). That’s all any grower needs, anywhere. Organic fertilizers (unrefined fertilizers) have all these things and, based on the ingredients, will also have different N,P,K ratios. But, they are all essentially the same. Which is really shocking considering how many companies of fertilizers are out there making crazy claims. If you haven’t noticed this, go check out a Cannabis-oriented hydroponics store. Since there are limits to how you can create fertilizers it is more than likely that most small, silly fertilizers are just buying one of the normal ones in bulk and repackaging it. They probably add some filler to make it look different.

Even organic ones can be excessively misleading, with their special, perfected recipes. Unless you’ve been a heavy chemical user for pest, fungi or weeds, your soil has the bacteria needed to break down raw materials into fertilizer. So all you really need is a nitrogen source (urea), sand of various rocks high in P or K or kelp or bone, blood, sea shells… etc. The quicker your plants respond to it does not mean it is a better fertilizer, it means it is being made available quicker. And therefore, waste and run-off is high. Chances are, your own compost is perfect for your plants and maybe one or two micro nutrients are needed to boost natural soil deficiencies.

Amaranth, beets, chard and spinach are all in the “beet” family. Some of them send roots as deep as nine feet and bring lots of micro nutrients to the surface. (Which is why they are so good for you.)


Use chemical fertilizers as plant medicine. Use a reputable name brand. You’ll find you need to use them in potted plants, as roots are restricted and nutrients are less available. The rest of the time use a form of organic fertilizer that benefits your soil structure (compost based), your soil deficiencies (if you’re low in one particular thing) and your pocket book. Consider where it’s coming from, to reduce your carbon impact.

Understand that there is a give and take. Rich, fast plant growth will result in problems with plant pests. Either lay-off the fertilizer or acquire beneficial insects and be proactive. (Flower growers do this if the plants are behind schedule for big sales times like Mothers Day. They’ll plan a “push” using higher fertilizer levels but will order more beneficial insects to be there ahead of the “push.”) Do not assume plants need your help at all. More often than not, poor soil structure and shallow root depth result in nutrient deficiency signs. Compost or fertilizers may be a quick fix, but loosening soil to 24 inches and mixing in organic matter will correct future deficiencies.


Perhaps we need fertilizers going forward to feed our growing population in less space. But, we will face problems. Fertilizers are not always a renewable resource. Consider the process. Even in my garden (totally organic, fertilized with compost generated on site), it is not a closed system. I eat the produce. That waste goes into the sewer and out to sea. Now think of billions of people pooping out our resources into the ocean. It is not by accident that we fail to deal with our waste directly. It is built-in: we have evolved to distance ourselves from our waste to avoid disease. But, perhaps we need to overcome this. A properly functioning outhouse is a great way to maintain nutrients on the property. But could we all have outhouses? Not in a high rise! So some companies are working on this. First they remove any possibility of transferring disease, but also finding a cost-effective way to remove any heavy metals or other contaminants that might damage plants. As gross as it sounds, spreading human waste into our fields is problably something we’ll need to do in the future. Until that happens, consider this. If you have a dog, try composing the dog poop with lots of carbon (wood shavings or brown plant material) to reduce the smell and spread that, not in a food producing crop but maybe into something like a flower garden. The waste (compost) you get from the flower garden can be composted and added to produce areas the year after. If that’s too much, then at least consider picking up aged bags of manure from time to time and adding them to your garden. It’s like brown gold!

Grains to an incredible job of bringing micro nutrients from deep in the ground up to the surface to add to your compost.

Learn more:

Vermicomposting (worm compost)

Attracting beneficials in your soil with compost

My garden plan

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