It’s that the time of the year where all you hear about is fertiliser. When do I fertilise, how do I fertilise, which fertiliser do I use… as a new plant parent it can all be bit daunting. I’m here to tell you there is no one-fit solution or clear cut answer. This is how I understand it and use it.

Plants need minute quantities of minerals over time. These minerals are Nitrogen (N) which helps with foliage growth, Phosphorous (P) which helps with root growth and flower development and Potassium (K) which helps with general cellular functions. Often, fertilisers will also have other nutrients in them too like calcium, magnesium and sulfur.

In nature, organic decaying material will provide these minerals for the plant. However, for an indoor plant with a limited amount of soil and minerals present, fertiliser is used to replicate this mineral makeup.

The Science

The makeup of fertiliser will often be called the N-P-K ratio. For example, if you see 15-30-15 on your Fertiliser’s bottle, it means that the fertiliser contains 15% Nitrogen, 30% Phosphorous and 15% Potassium. Fertilisers with larger numbers like 20-20-20 are more concentrated than those with lower numbers like 1-1-1 when mixed according to the instructions.

The speed at which your plant processes the fertiliser is heavily dependent on the light it receives and the temperature of the room. The higher the temperature and quantity of light the faster the plant processes the fertiliser. Water can also impact this process as water will often wash away the minerals and nutrients over time, so the more you water your plant the more minerals will be washed away. Often in low light areas what then happens is that the fertiliser isn’t processed properly and unused mineral salts then accumulate in the soil leading to over-fertilising issues.

When should you fertilise?

  • If you’ve had a plant for a while that hasn’t been repotted, its soil may start to become depleted in minerals.
  • Plants use more nutrients when they are growing well, so if you see your plant putting out leaves or growth (even if its in winter) then you should consider fertilising it. This generally occurs more often than not in Spring and Summer.
  • When you use semi – hydroponic or hydroponic methods of growing your plant where they are in media that are void of minerals (For example: perlite, LECA and water).

How often should you fertilise?

  • Take into account the environment your plant is in (light, water, temperature) because this determines how fast your plant is using up the minerals.
  • Sometimes it is better to fertilise your plants with smaller quantities over time than a large quantity all at once. If this is what you decide to do, you then need to adjust your routine to the fertiliser mix instructions. So, say the label says your dilution should be applied once a month, but you’d rather water once a week, then you should divide your solution by 4. If you want to apply it twice a week then you’d divide it by 8. Hello Math my old friend.

Take note

  • Over-fertilising your plant can be very bad. The nutrients in the soil become toxic and will lead to number of problems such as burnt roots and discoloured leaves.
  • Fertiliser is not a cure for a sick plant. And unless your plant has a nutrient deficiency giving it fertiliser might worsen the situation.
  • If you suspect you have over-fertilised your plant, then you can flush the excess fertiliser out with lots of water.
  • Fertilising one’s plant by spraying the fertiliser on the foliage as apposed to directly into the soil became a popular thing to do when research indicated that leaves are efficient organs at absorption. This has since become common place. Arguments against this is that most of the fertiliser drops off the leaf in any case and goes straight to the soil where it fertilises the plant in the normal way. As a hobbyist, I personally don’t see a huge difference in either method of application and so don’t have a preference.

My Stash

So here are the fertilisers that I’m currently using:

1. Tru Grower

I would buy this fertiliser just for its pretty packaging. I mean wow. Other reasons why I like it: It’s organic; it’s a liquid fertiliser so its an easy application process and you can control the quantity of fertiliser that you give your plants; you can spray the fertiliser on the foliage or water it straight into the potting medium. If you’d like to purchase this fertiliser, you can use my code SAFFRON20 on the Agrohort site to get a 20% discount. PS if you’re a subscriber to the Saffron’s Garden Plant Club, you might just get some in the November box!

2. Canna-Kelp

I discovered this brand purely by word of mouth and I must say I haven’t been disappointed. It’s generally only sold to wholesalers, so I was lucky to get some. This fertiliser is a paste that you dilute much like a liquid. It goes a very long way and it’s mainly made out of the super hero ingredient – kelp! Also being organic I was surprised that it has quite a mild smell which is great for indoor plants. If you’d like to buy some, I have a few available pouches online for R50.

Besides these two amazing fertilisers, other brands that were recommended through crowd sourcing were Umya and Seagro.

I hope this has helped you understand fertiliser a bit better. Let me know if you have any questions, or recommendations in the comments below.