Even if you are lucky enough to start with great soil, as your plants grow they absorb nutrients and leave the soil less fertile. By applying fertiliser to your garden or vegetable patch you replenish the lost nutrients and ensure that your plants have the food they need to flourish. 

Primary (Macro) Nutrients 

There are 3 primary nutrients that plants require in fairly large quantities.

These are Nitrogen, Phosphorus and Potassium:

  1. Nitrogen (N) stimulates new tissues and gives plants the green colour and abundant healthy new growth. Lack of nitrogen shows up as general yellowing (also called chlorosis) of the plant’s older leaves
  2. Phosphorus (P) stimulates root and shoot growth. Symptoms of phosphorus deficiency include stunted growth and inhibition of root system development
  3. Potassium (K) stimulates fruiting and flowering of plants and also improves the overall health of plants. Symptoms of potassium deficiency include brown scorching, curling of leaf tips, and yellowing between leaf veins

Apart from the above, plants also need oxygen from water and air, carbon from carbon dioxide in the air, and hydrogen from water and air. 

Organic Fertilisers vs. Synthetic Fertilisers 

Organic fertilisers are made of naturally occurring mineral deposits and organic material such as manure. It is not water-soluble and is released over a period of weeks, even months. Organic fertilisers stimulate beneficial soil micro-organisms and improve soil structure. Applying organic fertilisers and compost will, in most cases, provide all the secondary and micro-nutrients for a plant’s need. 

Synthetic fertilisers are water-soluble and can be taken up by the plant almost immediately. Synthetic fertilisers may be made from petroleum products, rocks or even organic sources. They give plants a quick boost but do little to improve soil texture or improve the soil’s long-term fertility. 

How do I choose a fertiliser?

The three numbers that you see on a fertiliser label, such as 3:1:5(26)SR, tells you what portion of each macro-nutrient the fertiliser contains. The first number refers to nitrogen (N), the second to phosphorus (P) and the third to potassium (K). This NPK ratio reflects the available nutrients by weight contained in that fertiliser. The fourth number is always found in brackets and is the percentage value of the whole product that is pure fertiliser in the said ratio – that is, how concentrated the fertiliser is. In this example, 26% are fertiliser with 74% being the filler. The SR letters stand for Slow Release, meaning this fertiliser is not instantly available to the plant. It is released in even, regular doses to the plant, and lasts longer so that means future applications need be further apart.

Fertilisers are a quick and convenient way to add nutrients to your soil, but always remember to use compost together with fertiliser for best results. 

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