Ever wondered what "N.P.K." is all about? Well the below info gives a short summary of the basics in fertilising your garden.

N in NPK: Nitrogen

Nitrogen is absorbed and used by the plant to produce leaf growth and general formation of stems and branches. Basically, the more leaf a plant produces, the higher its nitrogen requirement. Plants most in need of nitrogen will mainly include grasses and leafy vegetables such as cabbage, lettuce and spinach.
Although around 80% of the atmosphere is made up of nitrogen, most plants cannot utilise 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 fertiliser 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 discoloured leaves.

Application of Nitrogen

Nitrogenous fertilisers are quickly washed out of the soil by rain and need to be renewed annually. With crops that require a lot of nitrogen over a period of time, like cabbages, adding nitrogen incrementally through the main growth period is the most efficient application method.
Gro Natural Fish Emulsion is a great source of Nitrogen (along with Phosphorus and Potassium

P in NPK: Phosphorus

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.

Shortage of Phosphorus in Plants - Symptoms

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

Application of Phosphorus

Phosphates remain in the soil for two or three years after application so the amount in a general fertilizer is probably enough. Add just before planting or top dress during growth periods.

K in NPK: Potassium

Potassium 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.
Take note that Potash is potassium and vice versa when discussing fertilisers.

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.

Application of Potassium

Potash usually last for two or three years in the soil but for vegetable production (tomatoes, potatoes especially) additional will be required. This can be applied as a liquid feed, for tomatoes or a specially prepared fertiliser, high in potassium for potatoes.

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