Plant Care: Fertiliser 101

by Sarah Gardiner

Sarah is a horticulturist with a passion for edibles and cottage gardens.

We all know that plants need water and light to survive - but what about fertiliser? Standing before shelves full of dozens of different options can certainly leave us feeling overwhelmed or confused - and that’s before we’ve even started to take in all the information on the labels. Let us talk you through it… how they differ, what you should choose and the best time of year to apply it.

What is Fertiliser?
Plants make their own food through a process called photosynthesis - so fertiliser is not food. It’s more like a concoction of vitamins similar to those that plants would be able to absorb from the soil in their natural environments. Without applying fertiliser to your plants, you might find that they survive rather than thrive. They might start to lose their colour, or slow down with the new growth they are putting out. Fertilising is a relatively simple step once you get the hang of it, which is often overlooked without people realising how vital it is to growing lush, healthy plants.

Why is it important?
As plants grow actively throughout its growing season, the essential nutrients within the plant and your soil will be lost and need to be replaced for the plant to continue to thrive. Applying fertiliser will replenish the soil so your plants can continue accessing the nutrients they need.

What does NPK mean?
One thing most fertiliser labels will have in common are the numbers we refer to as NPK. N is for Nitrogen, P is for Phosphorus and K is for Potassium. These are the three primary macronutrients for plants and the most important nutrients to understand. To put it simply, Nitrogen is responsible for leafy growth, Phosphorus contributes to strong root systems, fruiting and flowering, and Potassium is for healthy cells, pest and disease prevention. When looking at the NPK breakdown - the higher the numbers on the label, the stronger the concentration the fertiliser will contain. For example, organic, liquid fertilisers might have an NPK that looks something like 6-1-4 vs a chemical, crystal fertiliser that has an NPK of 20-9-16. It might be more appealing to use a fertiliser that is stronger, however this has more chance of fertilisers accumulating in your soil and causing issues in the long run.

What should I choose?
Fertilisers come in a range of different forms and whether you opt for a fast-release liquid or slow-release pellets, you’ve reached the first step. Choosing a fertiliser to suit your needs is important, so that it fits into your schedule and isn’t a chore. Generally speaking, liquid fertilisers are applied in smaller doses more often. Alternatively, choosing a slow-release fertiliser will mean it feeds slowly over the growing season, so it can be applied less frequently. It is worth noting that slow-release fertilisers are stronger and contain more nutrients - so make sure to read the label and apply accordingly, as using too much or applying at the wrong time of year can end in tears.