fertilizer? Let’s get some basics here

An alert reader heard about a friend who was trying to feed her plants necessary nutrients using the sports drink Propel. Propel had a small amount of potassium in it and I suppose, the person had heard that potassium was good for plants. I have to admire the creativeness while discouraging the idea for being impractical.

This has led to some ideas about blog posts regarding fertilizers. I have touched on some aspects of plant food in other posts, but this Propel question must lead to a better understanding on this blog. This may take a few days so hold on and let’s get started with Nitrogen before we get all the way to Propel and her Potassium.

Let’s do a little review of plant food. The first and most important plant nutrient is water. I think we can all agree that we can control the growth of plants and even their life by controlling water. This concept is so basic it is often overlooked as a crucial tool for growth and development. I say this not as an aside, but as a concept in plant nutrition before we get to the stuff you can buy in a bag. Remember, the water is the most important. Now here we go on the stuff in the bag.

Mostly what we talk about when we say “fertilizers” are the big three macronutrients, Nitrogen, Phosphorus and Potassium. These three, in that order, are listed in a standardised format on all plant food labels. There is a good reason they are in that order; they are listed in order of their importance to the plant.

Let’s look at some characteristics in the soil of these three elements. I say elements because they are indeed elements on the periodic table of chemistry. Nitrogen (N) is used in the largest amount by the plant, then Phosphorus (Ph), then Potassium (K).

Nitrogen is the cheapest nutrient in most fertilizers, and will do your plants the most good. Nitrogen is water-soluble in soil and must be constantly resupplied to give your plants the food they need. Since it is water-soluble, rain will wash it away down into the soil and your plants will be sad until you give them more. Natural soil has various amounts of it and it comes from decomposing humus on the forest floor. As animals and plants rot away, the N is released and set free for plants to eat up. Also, rainwater contains small amounts that constantly feed earth’s plant cover a little bit. In a few plants, (mostly in the pea family) Nitrogen fixing bacteria take atmospheric N and convert it into usable N in the roots.

Commercially available animal manures or chemical fertilizers will give your plants the most improvement due to their Nitrogen content. Differences in the rate of release of N in different formulations can impact the growth of your plants. Let’s take the spectrum of N sources and look at their release rates. The most classic chemical source of N is Urea. Urea is named for urine (duh) and in the dry pellet form available in bags. It is relatively high in N (about 33% plus or minus a bit) and is immediately soluble in water and thus available to the plant. If you use too much, you will form a water solution with specific gravity higher than the juices inside plant cells. This can pull water out of the plant cells and burn the plant. You want to use this form of N sparingly and dilute with a lot of water. All the N from urea will go into the water and feed your plant and begin washing away. This gives a big quick burst of N and then nothing as the N washes down deep in the soil. If I were using this form of N for my plants, I would use it sparingly but frequently.

Nitrogen also comes in chemical fertilizers in forms called “WIN” which stands for water insoluble Nitrogen. WIN is a very good thing in fertilizers because it time-releases the N and constantly feeds the plants a little at a time. This is very good because it does not run off and cause pollution and your plants can happily feed on just a little N all the time which they really like. It is created by coating the little round balls of fertilizer with a slow dissolving coating. Sulphur coated urea is a common version. The fertilizer bag will say what percentage of WIN is in the mix. The more the better. The fertilizer manufacturers want as little as possible because it is an expensive type of N. Usually a fertilizer mix will have a little uncoated urea for a quick green up and then some WIN to keep feeding all season long. This is my favorite type. No need to keep applying it since the little prills are timed-release. This gives Infamous more time for blogging.

Another version of timed release is the use of natural animal manures. They contain Nitrogen bound up in the organic material of the manure. The manure has to be worked on by microbes in the soil before the N is released so by necessity, it comes out slowly, kind of “timed release” in a natural way. The only drawback is that manures are usually only about 2-3% N whereas you can get up to 33% in chemical urea. You need a whole lot of animal manure to equal a chemical product. It is also pretty expensive comparatively. On the plus side, you will probably never burn anything, so that is something. Any of you gardeners out here who are overly enthusiastic and tend towards a heavy hand, should probably use manure.

Well, that is all today about nitrogen. Tomorrow will be Phosphorus and then Potassium and finally Propel water. I guess wacky ideas about gardening can lead to good ideas for blogs.

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2 Comments

  1. Kevin said,

    June 23, 2010 at 11:39 AM

    Specific gravity of a solution isn’t the reason it dries or hydrates a plant, I don’t think. The concentrations of solutes is (tonicity), which happens to correlate with specific gravity.

    • infamousginger said,

      June 26, 2010 at 7:35 PM

      Good comment, you are right as always. But you sure can burn up plants with too many soluble salts in solution outside the plant roots which draws water OUT of the roots and dehydrates them. Tonicity it is then.


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