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Slow Release vs Liquid Fertiliser: When to use and what is the difference?

Yup its another fertiliser post, but this is a question we get asked so often its time to throw it out to the SEO gods and hope it gets read.

Slow Release vs Liquid Fertiliser: What is the difference?

When talking about slow release fertilisers, we are talking about any fertiliser (synthetic or organic) that has been pelletised or produced as something that will slowly release nutrients into the soil over a period of time. NPK can vary, depending on the product and if it is organic or synthetic (we've discussed these apects of fertiliser here). Some of the most common and well know slow releases are found in hardware stores across the country un the form of small, coloured balls. These are fertilisers coated in a plastic resin or sulphur-based polymers and they slowly break down when exposed to variables like heat, light and water. They are not organic. Organic slow release fertilisers like our Bio Pellets act in a similar fashion, although the nutirents are released into the soil as the pellets start to decompose when all the beneficial microbes start working their magic.

Benefits of Slow Release Fertilisers include:

  • Lower risk of fertiliser burn/toxicity because small doses of fertiliser is released slowly over time.
  • No need to remember a regular fertilising routine - can apply less frequently. 

That being said, those same benefits can cause a few headaches when using on potted or indoor plants. Higher NPK slow release fertilisers (like those balls I mentioned above) are harder to predict indoors. Temperature and light can vary and the potted plant might not get enough (or too much!) fertiliser over a period of time. As the plant is in a pot, the excess fertiliser can build up. For this reason, we always recommend only using organic slow release fertilisers on potted or indoor plants.

With liquid fertilisers we are referring to a liquid-based, organic or mineral, fertiliser.  Liquid fertilisers are faster acting as there is no need for any decompostion or break down and can be absorbed by the plant as they draw water up from the soil. Again, the NPK will depend on what sort of fertiliser you are using. 

Benefits of Liquid Fertilisers include:

  • Fast acting - you'll see results quicker
  • more control - you have complete control over the application rate, meaning you're not at the whim of variables like the weather. 

The big risk with liquid fertilisers is overfertilising. If the directions are not followed and the dilution rate is incorrect, you can risk harming your plant. When used correctly though you can't beat their results. 

What type of fertiliser is best for you and your indoor plants?

Both fertilisers have their advantages and we have always been big proponents of a blended approach. During the growing season (usually Spring and Summer) we recommend using a high Nitrogen liquid fertiliser. It is quickly absorbed by the plant andwill reward you with larger foliage and more growth. 

When the weather gets cooler and there is less light available, we typically see slower (if any) plant growth. It's a bit of a myth to cut fertilising out all together over this period - a better option is to use an organic slow release plant food. This not only reinvirgorates the potting media so its full of life come Spring, but also provides the plants with much smaller doses of the macro and micro nutirients they need to live their best. 

What type of fertiliser is best for outdoors?

Outside its a different story. Whereas indoors the plants are 100% reliant on you to provide them with their nutrient fix, outdoors your plants are able to collect some of those nutrients themselves, in the form of decaying organic matter like leaves or dead insects, and through worm castings. The key outdoors is to ensure your soil is full of life - the more microbial life, the quicker organic matter is broken down creating a nutrient-rich bed for your plants and for other beneficial life like worms. 

As such, outside we recommend using an organic slow release fertilier like our Bio Pellets or even our Soil & Microbe Booster. Not only do both these products release supplementary nutrients into the soil, but they also add microbial life to help improve the soil structure, which in turn helps with plant health and nutrient uptake.

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