N.P.K. Explained

N.P.K. Explained

We get asked a lot this time of year what fertilizer should be used on what plant. I find the subject very interesting, much to the dismay of some callers who I sense nodding off on the other end of the phone! Anyway a good basic knowledge of what fertilizer is will enable you to make an informed choice and give your plant the feed it needs.

The German scientist Justus Von Liebig came up with the theory that Nitrogen, Phosphorous and Potassium are mainly responsible for healthy plant growth. While this is true it doesn't take into account the whole host of other essential nutrients and the importance of beneficial micro organisms which help your plants thrive and fight of pests and diseases. Of course a healthy soil is the most important thing for the vegetable gardener, liquid and granular feeds can be used when growing in limited space (growbag) or as a top up while you are improving your soil.

Before you look at adding any fertilizer it's important to do a soil test to see if anything is lacking. Interestingly the major problem of excess fertilizers running off into waterways come not from the agricultural sector but more from the home owner. Did you know the home gardener uses 10 times the amount of fertilizer a professional farmer uses? It makes sense if you think about it, fertilizer is expensive so the farmer is trying to use as little as possible, we on the other hand tend to be a bit trigger happy! Adding more fertilizer than the plant needs is really a waste as it can't be used and will just end up leaching through the soil and eventually into the ground water.

Anyway, back to NPK:

N.P.K. There are three major elements essential for plant growth: N - Nitrogen - For stem and leaf growth. Nitrogen deficiency results in older leaves turning yellow with new growth being weak and spindly. Essentially responsible for the strength and vigour of you plants. P - Phosphorous - For root growth and photosynthesis. Symptoms of deficiency would include poor germination and establishment of seedlings, mature plants showing stunted growth and dark blue/green leaves or reddish-purple stems or leaves. K - Potassium (Potash) - For flower and fruit production. Lack of Potassium results in yellow areas along leaf veins and leaf edges. Fruits like tomatoes may be stunted and lacking in flavour.

Tomato plant photo

These are your main powerhouse elements and the main components of all fertilizers. The amounts vary depending on what you are trying to achieve. For example a general fertilizer would have equal amounts of each but a tomato feed will have more potassium for the production of tomato fruits. If you are looking for strong leafy growth for cabbage for example a feed high in Nitrogen is what you need.

We would recommend keeping your soil in good condition by adding plenty of organic matter and using less harmful organic fertilizers when you need to give plants a boost. Remember all these important elements occur naturally so you don't need to resort to chemical fertilizers to get them. The best all round product we have found for feed during the growing cycle is ‘seamungus’ poultry manure and seaweed pellets. Poultry manure is high in Nitrogen while the seaweed provides an impressive list of minerals and trace elements. For a fruit and tomato feed we highly recommend Irish tomato and fruit feed.

The most accurate way of applying fertilizer is to first test your soil to check for any deficiencies, you can then tailor your fertilizing regime to suit. We stock a simple and easy test kit on our website for this purpose.

Other major elements Ca - Calcium - Used to transport plant nutrients internally. S - Sulphur - Used for protein production. Mg - Magnesium - Essential in production of chlorophyll.

These guys are less likely to be a problem and are easily sorted if they are. Both Calcium and magnesium deficiencies are cured by our cal-sea-feed. Sulpfur is included in the ‘Seamungus’ pellets.

Trace Elements B - Boron Cu - Copper Fe - Iron Mn - Manganese Mo - Molybdenum Zn - Zinc

Trace elements are only needed in tiny quantities so are unlikely to be a problem for the domestic grower. Deficiencies are very rare and good rotation, use of garden compost and manure will cure them.

Digging in organic compost to improve your soil.

In general Vegetable plants are far hungrier than ornamental plants so you will need to add a fertilizer at some stage. We prefer to use organic fertilizers as they are kinder to the environment. I would stress that the use of compost, mulch and manure is the best way to improve the soil in the long term. The pelleted and liquid feed we supply are best used as a top up to a well balanced soil.