How does a fertiliser work?

Have you ever wondered how a plant fertiliser works? Maybe you’re concerned about the environment and would like more details, or perhaps you’re just curious? This article should tell you a little bit more about using fertilisers in your garden, why they’re needed and the effect they can have on plant growth.

What is a plant fertiliser?

A fertiliser, often referred to as plant food, is a broad term for either a mixture of chemicals or naturally occurring matter that is used for enhancing the growth of plants.

You can add fertilisers to the soil in liquid, water-soluble and granular form or purchase compost with it already mixed in. There are also a number of organic fertilisers available such as Chicken Manure and Bone Meal.

Plants, whether they are flowers, fruit or vegetables, need a number of nutrients to grow well – along with a good watering and adequate sunlight. When you buy bagged compost from a garden centre, many have a balanced quantity of fertilisers already added to give your plants a real boost, but how does the fertiliser actually work?

Mixing Miracle-Gro All Purpose Plant Food Liquid in a watering can

How do fertilisers work?

Fertilisers work by providing essential nutrients to developing flowers, trees and veg, as a kind of multi-vitamin or meal replacement for the plant world. Many fertilisers also improve the way the soil works by helping it to retain water better and allowing air to flow freely, which is good for roots.

The main ingredients in most popular fertilisers are ‘N’, ‘P’ and ‘K’ - the basic elements required in plant growth - Nitrogen, Phosphorus and Potassium (which has the chemical symbol K).

The Nitrogen element works by increasing the plant’s capacity to produce new stems, flowers or fruit. It also increases the speed at which it will grow and improves the quality and appearance of the foliage. You will probably have seen its effects in dramatic before and after photos comparing the use of plant additives to not.

Phosphorus helps the plants produce all of that nice organic stuff like oils and starch which is great for forming large, strong root systems. Phosphorus also helps the plant to develop Chlorophyll, which allows it to turn solar energy into chemical energy (photosynthesis). Combined with Potassium, Phosphorus helps produce healthy flowers and fruits in abundance.

Lastly, Potassium helps to build protein, fight off diseases and, just like Phosphorus, is essential in the process of photosynthesis.

All of the above are required to work together to produce a good healthy plant, if just one of these valuable nutrients are missing or lacking your plant will struggle to produce fruits or flowers of the highest quality.

Comparison of unfed versus fed plants

What else do plants love about fertilisers?

Nutrients normally occur naturally in well maintained soils but if there’s a drainage issue or other problem, nutrients can soon disappear. Adding a fertiliser is a way of giving nature a helping hand.

Natural and man-made fertilisers can contain a variety of ingredients, but here are a few of the most important ones for plants in addition to the standard Nitrogen, Phosphorus and Potassium as described above: Zinc, Magnesium, Calcium, Sulphur and Iron.

You can also get fertilisers that are fit for the purpose of a specific plant or species. These are important as different plants, like Camellias for example, require a careful balance of certain nutrients. If a general purpose fertiliser is used it may not provide all the valuable nutrients this type of plant requires.

Looking for an alternative? Types of organic fertiliser

There are two types of fertilser, those that are derived organically from plants and animals, which include

These types of organic fertilisers are made up from big molecules, so it takes a long time for soil organisms to break them down, in order for them to be easily absorbed by plant roots.

The second is the inorganic fertilisers that are made from synthetic natural plant materials or natural chemicals that are mined, such as:

These are faster acting than organic fertilisers due to being more concentrated.

What are the drawbacks of using fertilisers?

We have focused a lot on the benefits of using fertilisers and it is thought that between 30% - 50% of what our crops produce are a direct result of these additives, but there must be some negatives?

If a fertiliser is used incorrectly or at a higher consistency than recommended, it can cause damage to foliage like a chemical burn. Plants will normally recover from this but younger, more fragile ones may not.

Some inexperienced gardeners might think that adding a fertiliser is all that’s needed when growing plants. However, just like human beings, plants also need a balanced diet and a number of other elements to be able to grow to the best of their ability. For a human a mixture of vitamins and minerals in a variety of forms are required and the same can be said for plants. A well maintained soil with worms and insects is essential to adding oxygen and producing organic matter to the growing medium.

Now that you have more of an understanding of how fertilisers work, you should be able to put them to better use. As with all additives, less is often more and it’s about getting the right balance for your plant.

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