Often referred to interchangeably, plant food and fertiliser both feed plants but have very different sources. One type of plant food is for cut flowers, and although ingredients between different brands can vary, those little flower food sachets contain mostly sugar, a little citric acid, and a tiny bit of bleach. The citric acid balances the pH level of the water which means flowers will be able to drink faster and reduce wilting. Aspirin is also a tried-and-true way to revive and keep roses and other cut flowers for longer – add a crushed aspirin to the water before adding your flowers, but don't forget to change the water in the vase every few days.

Is plant food the same as fertiliser?

Firstly, real plant food Is made by the plants themselves, using elements derived from air, water, sunlight, and nutrients in the soil. Fertiliser is also food for plants, but it’s derived from a mixture of natural or synthetic nutrients added to soil or water (or sometimes applied to foliage) to supplement a plant’s health and growth.

Both plant food and fertiliser contribute to a plant’s overall health and growth, unfortunately, the terms often are used interchangeably, which could lead to confusion.

Plants make their own food

So, what is plant food made of exactly? A complex question, so bear with me. It’s a byproduct produced by plants, which convert water, carbon dioxide, sunlight, and soil nutrients into sustenance for themselves. It’s taken from the soil through their roots, and during photosynthesis, plants convert sunlight, carbon dioxide, minerals, and water into sugars and oxygen. They release that oxygen into the atmosphere and use the sugars as food.

Fertiliser is an additive that you can make or buy

Fertilising plants increases the nutrients necessary for healthy plant growth by adding them to the soil. Gardeners can make their own fertiliser, often using common household ingredients such as baking soda, ammonia and Epsom salts, or choose from the many commercial brands which come in a variety of forms: liquid, granules (either slow-release formulas that last a growing season or quick-release types for immediate effect), and spikes. Fertilisers can be organic or inorganic. It’s important to know your plant’s needs at various stages of its life to make the best selection.


The major nutrients a plant needs are nitrogen, phosphorus, and potassium. These three are combined in different proportions, commonly referred to as the NPK ratio, to target various types of plants. A balanced fertilizer features equal amounts of all three elements.

In addition to these, plants need small amounts of other micronutrients for healthy growth - trace amounts of some help fight disease; others help plants resist insects. For example, zinc helps plants develop roots and undergo photosynthesis, as does iron, which will aid chlorophyll production. Boron assists in flower development, amino acid aids production and sugar transport.

Organic fertilisers are carbon-based and usually comes from plants and animals - composted manure (cow manure has the most nutrients), bone meal, and blood meal. Because they must break down in the soil to be of benefit to the plant, organic fertilisers can take longer to be effective. However, their effect is often longer-lasting.

Inorganic fertilizers are generally derived from synthesised chemicals containing nitrogen, phosphorus, and potassium. These synthetic fertilisers tend to be highly concentrated and feed plants, as opposed to enhancing soil. While chemical nutrients are considered ‘purer’ in form, they act faster thanks to their water solubility, but they are often more expensive.

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Too much fertiliser can do more harm than good

Too much of a good thing could harm plants, overapplication results in fertiliser burn, which could cause yellow or brown foliage or root damage, and salts in the fertiliser draw out too much moisture. It can also force plants to grow faster than their roots are able to support them, creating weak plants – for instance over-feeding tomatoes with high-nitrogen fertilisers creates big, leafy green plants with few flowers and fruits. If you accidentally over-fertilise a plant, the best remedy is to flush the soil with water to help remove the salts.


Marilyn writes regularly for The Portugal News, and has lived in the Algarve for some years. A dog-lover, she has lived in Ireland, UK, Bermuda and the Isle of Man. 

Marilyn Sheridan