Fertilizer

Fertilizer is one of those things that falls under the, “Too much of a good thing is a bad thing” category. All too often, at the first sign of unhealthy plants, people grab a bag of fertilizer before checking for inhospitable soil conditions, unhealthy roots, irrigation problems, nutrient toxicities, and pest or disease infestation. ​

1907 fertilizer advertisement (Union Guano Company, Winston-Salem, NC, USA) Public domain

Different plants have different nutrient needs. Simply dumping a box of 10-10-10 around the garden isn’t a good idea and it’s a waste of money. The chemicals can leach into ground water, burn sensitive new roots, and damage beneficial soil microorganisms. It can also make plants grow faster than they can maintain over the long haul, leaving them weak and vulnerable later in life. Many woody ornamentals never need to be fertilized, even when they are first planted, while containerized plants need regular fertilizing.

Fertilizer burn (Fenrisulfir) CC BY-SA 3.0

​N, P & K

Most gardeners are familiar with the three numbers displayed on bags and boxes of fertilizer, but we’ll do a quick review, just to be sure. Those three numbers represent the percentage by weight of nitrogen (N), phosphorus (P) and potassium (K). Think about this for a moment. A 10-pound bag of 10-20-10 fertilizer contains 1 pound nitrogen, 2 pounds phosphorus, 1 pound potassium, and 6 pounds of filler. Yes, filler. If all your plants need is nitrogen, blood meal may be a better choice.

Plant nutrients

Plants use 16 chemical elements as food. Those elements include oxygen, carbon, and hydrogen, along with 13 mineral nutrients. Those mineral nutrients are broken down this way:
   Macronutrients
        Nitrogen (N) - leaf growth
        Phosphorus (P) - root, fruit and flower growth
        Potassium (K) - stem and cell growth
    Secondary Macronutrients
        Calcium (Ca)
        Magnesium (Mg)
        Sulphur (S)    
    Micronutrients
        Copper (Cu)
        Iron (Fe)
        Manganese (Mn)
        Molybdenum (Mo)
        Zinc (Zn)
        Boron (B)

Soil tests

Before applying fertilizer, invest in a good soil test. It’s worth it. And it’s a fascinating snapshot of what is really going on in the garden. Now, I don’t mean one of those over-the-counter test tube kits. Those are a waste of money, in my humble opinion. When searching for a soil lab, it is best to pick one near you. The east and west coasts have very different soils (ours is alkaline; theirs is acidic, for one thing). This means that different types of tests are used to analyze soil samples. 

I learned some surprising facts about my soil when I sent in a sample. Most important, I learned that my soil already has a ton of everything, except iron. Without iron, the plants weren’t able to absorb the abundance of available nutrients. Adding fertilizer would have been a complete waste of time and money. Instead, because I had the knowledge, I was able to apply a foliar (leaf) spray of iron and my garden plants had access to everything they needed! So, get your soil tested before adding anything.

Types of fertilizer

If you are like me and prefer a more natural approach, use compost instead of fertilizer. Since I raise chickens, composting is even more effective. Chicken poop is high in nitrogen, and practically anyone can raise hens or build compost. Yard and kitchen scraps that would normally end up in landfills can be transformed into nutrient rich compost that that also improves soil structure.

If you decide fertilizer really is necessary: READ THE BAG. Seriously. Federal law requires that specific instructions and useful information are printed on the container, and for good reason. Follow directions carefully and wash your hands when you’re done. Technically, there is no chemical difference between nitrogen from compost and nitrogen formulated in a lab. Nitrogen is nitrogen. The difference lies in everything else. What are the fillers? What else is in the compost that plants need? Honestly, there’s a lot we don’t yet understand about how living things interact. I prefer to err on the natural side, just in case.

​For a hysterical read about the effects of too much fertilizer, check out Don Mitchell’s Moving/Living/Growing Up Country series.