Fertilizer: magic potion or toxic formula?

By Michael Smith (Veshengro)

What is fertilizer and is it bad for plants and soil or not?

So, for a start, let's do the fertilizer crash course. On a bag of fertilizer you will see three numbers like 12-12-12 or 18-6-4 or 5-36-5, though in some countries this is done a little different. Here's what the numbers mean and what they mean to you as a gardener. Those numbers also can be represented with the addition of the letters N = nitrogen, P = phosphorous and K = potassium, aka kalium in Latin, hence the K.

The first number is the percentage of nitrogen in that particular bag of fertilizer. Plants need and love nitrogen, but like many things that you may like as well, too much of a good thing is not a good thing. So you have to make sure you are not putting too much nitrogen on any particular plant.

Although 78% of the atmosphere is nitrogen, most plants cannot utilize this. Plants in the bean family, legumes, have nodules on their roots where bacteria live that fix nitrogen from the air for use by the plant. They provide their own nitrogen fertilizer this way.

Shortage of Nitrogen in Plants - Symptoms

You can tell if your plants need nitrogen when their growth is stunted with weak stems and they will have yellowed or discolored leaves

The second or middle number on a bag of fertilizer is phosphorous. Phosphorous is like an under the hood tune up for plants. Phosphorous plays an important role by helping the plant absorb and use the nitrogen and other nutrients that a plant needs from the soil in order to be healthy and happy.

Phosphorous really aids in the photosynthesis process and essentially makes and keeps the plant healthy. Phosphorus is essential for seed germination and root development. It is needed particularly by young plants forming their root systems and by fruit and seed crops. Root vegetables such as carrots, swedes and turnips obviously need plentiful phosphorus to develop well. This means the plant will produce more flowers and fruit. So, basically, it takes the correct amount of phosphorous for plants to flower beautifully or to produce lots of good fruit.

Shortage of Phosphorus in Plants - Symptoms

Without ample phosphorus you will see stunted growth, probably a purple tinge to leaves and low fruit yields.

The third or last number on the bag of fertilizer is the percentage of Potassium in the fertilizer. Also called potash. It is represented often by the letter K, as mentioned already above.

Potassium, as already stated, has the chemical symbol K from its Latin name kalium. It promotes flower and fruit production and is vital for maintaining growth and helping plants resist disease. It's used in the process of building starches and sugars so is needed in vegetables and fruits. Carrots, parsnips, potatoes, tomatoes and apples all need plenty of potassium to crop well.

Potassium is naturally found in wood ash which is where it its name potash is derived from and potash is potassium and vice versa when discussing fertilizers.

Potassium gives plants stamina because it helps plants absorb and use water. Usually there is plenty of potassium in the soil, but much of it is not in a form that plants can absorb. The potassium in a bag of fertilizer is water soluble and easily absorbed by plants. Potassium helps plants survive drought conditions because it helps the plant use water more efficiently.

Shortage of Potassium in Plants - Symptoms

Plants that are short of potash will have low resistance to disease, scorching of leaves and poor fruit yield. Tomatoes will really show the effects of a shortage of potassium.

As potassium is potash, that is to say, wood ash this byproduct of wood burning for heating is a great addition to the garden soil – and was used for that by the cottage gardeners of old for just that reason – as is charcoal. A great homemade potassium fertilizer is made from comfrey and there are a number of ways as to how to do this.

Tomatoes and potatoes, both in the same family of deadly nightshade plants, bot require a very high amount of potash in order to produce a good crop. That is if your tomatoes don't get hit by the blight again and again, as mine have been over the last couple of years and for that reason I am going to give up on that particular vegetable which, actually, is a fruit.

So what does all that mean? That means that you have to use the correct fertilizer for the particular plant you are fertilizing. However, the fertilizer companies have made this easy for us because a lawn fertilizer has a very high amount of nitrogen because your grass grows a lot more than typical plants and grass needs and will use more nitrogen.

Grass clippings also should be mulched rather than collected off the lawn in order to have the nitrogen contained in the leaves go back into soil and into the growing grass itself.

So-called plant food fertilizers I suggest you avoid a little like the plague. They, like all the fertilizers used in commercial growing, do feed the plants but more often than not harm the soil and you really want healthy soil to grow plants, especially for food.

Good compost is one of the main things to consider and that should be applied as a “top dressing” before any plants are sown or planted and dug into the soil by means of a garden fork or a rototiller. Add some lumpwood charcoal into the compost and the mix and some mulch and you should be well on the way to having a great starting bed for your plants.

To answer the initial question as to whether fertilizer is a magic potion or a toxic formula it would be a case of: “it depends” and that means it depends on what you are using as a fertilizer. Some of the serious chemical ones are that, chemical, and are synthetically produced and but a plant food. They tend to harm the soil by leaching the goodness out of it. Thus it is a case of being careful. The best way is the “organic” way by making your own.

A real gardener doesn’t feed plants, he fed the soil which feeds the plants

© 2012