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How to find the right fertiliser for my indoor plants
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How to find the right fertiliser for my indoor plants

To help boost the growth of your indoor plants, you need to feed them. But, with so many different fertilisers and plant tonics available, what’s the best one? To help you decide, it’s important to understand what makes up a fertiliser and how plants use the ingredients to grow.

Why do I need to feed my plants?

Plants rely on nutrients to help them grow. More specifically, plants require nitrogen (N), phosphorus (P) and potassium (K), aka NPK, to develop healthy, strong growth. Nitrogen assists with leaf colour and development, phosphorus stimulates root growth and helps promote flowering, while potassium stimulates flowering and strengthens cell walls.

All fertilisers contain varying amounts of these essential or ‘macro’ nutrients, adjusted to different ratios to target specific growing needs. For example, leafy plants like Parlour Palm and Devil’s Ivy, require more nitrogen for lush, verdant growth, so there is little point in giving them a fertiliser that’s high in potassium as it will encourage flowering. Conversely, you want to promote flowering in African Violet and Peace Lily, so a fertiliser specially formulated with higher potassium is preferred.

African Violet

Your African Violet can benefit from a specially formulated fertiliser with a higher potassium (K) component.

But, this isn’t a sign to solely feed leafy plants with nitrogen or potassium – this will create an imbalance in nutrients and cause an overall decline in health. Do you feel good when you only eat a certain type of food? Yep, nor do plants.

Plants also need other nutrients, such as iron, magnesium, manganese, and zinc, but these are required in much smaller amounts. They’re called trace elements and are not typically something you need to worry about, except if your plants present signs of specific nutrient deficiency.

What type of fertiliser do I give my plants?

Now, you will find a plethora of different fertilisers at your local nursery. They may be organic, inorganic (synthetic), or a combination of both.

Organic fertilisers sound exactly like what you expect them to be – derived from natural sources, like composted animal waste, and blood and bone. Once applied, these fertilisers are broken down by microbes in the soil or growing media, which in turn, release nutrients for plant uptake. But this process takes time, so you’ll often see them referred to as ‘slow release’ fertilisers.

Worm tea is an organic fertiliser you can derive as a by-product of your worm farm. 
Photo by sippakorn yamkasikorn on Unsplash

Organic fertilisers, like Munash Indoor Plant Food are great as they nourish both the soil and the plant. While they don’t give plants an instant boost of nutrients, ‘feeding’ the microbes in the soil is key for overall plant health. To use on your CUP OF FLORA plants, sprinkle a pinch on top of the mix and gently blend in.

Inorganic fertilisers are made from a mix of naturally occurring minerals and man-made chemicals. The nutrients are available in ‘fast-acting’ format, so are readily available to plants. Also, due to how they’re manufactured, the ratios are perfectly balanced to suit specific plants. They’re great for boosting plant health and growth, but do not feed the soil.

Organic-based fertilisers are usually a combination of both organic and inorganic nutrients, giving your plants a complete, well-rounded feed. It’s worth noting, that the NPK is generally lower than that of pure inorganic fertilisers.

What form of fertiliser do I give my plants?

These types of fertilisers are available in liquid, soluble, prills, pellets, and leaf sprays. They all claim to give your plants the best feed. Not to say they won’t, but knowing how they provide your plants with nutrients will give you a better idea of what works best for you.

Liquid and soluble fertilisers are both dissolved in a watering can and applied to plants when watering. As plants take up nutrients in a liquid form, these types of fertilisers are fast-acting and perfect for when plants are actively growing. It is recommended you apply them once a week or fortnight, depending on the manufacturer. These fertilisers are ideal for plants in CUP O FLORA pots. To use, simply add a small amount of fertiliser to the reservoir in the outer pot and mix well. Top up as required during the growing season.

Pellets are mostly organic fertilisers and are typically composted organic matter (animals waste and manures) that has been dried and shaped into pellets. They break down slowly but are great for feeding the soil microbes. You may need to reapply once a month or once every few months but check the label for detailed advice.

Prills are small, round beads that are packed with essential and trace elements. They are usually ‘controlled-release’ fertilisers, so break down over time to give plants the right amount of nutrients, at the right time. Depending on the product, they can feed anywhere between 3-6 months (or longer). They are ideal if you prefer not to be feeding so regularly.

Leaf sprays are a convenient way to feed plants as you simply spray the leaves with the product. Plants can absorb the nutrients through their leaves, however, they do not travel as effectively throughout the plant as they do when applying fertilisers to the soil (plants take up water and nutrients via their roots). It’s good for pick-me-up spray, but not as a complete nutrition solution, so use it conjunction with other fertiliser types.

As you can see, there are a few aspects you need to consider when choosing a fertiliser. But understanding how they work and how plants use them, and then assessing how the price and ease of use fits into your life, will help you pick the right one. No matter what format you choose, your plants will get a good feed.

About the author

Tammy Huynh is a horticulturist, garden writer and presenter. She writes for various publications, including Bunnings Magazine, House & Garden, and Gardening Australia. Tammy is an avid indoor plant collector and passionate outdoor gardener and loves sharing her knowledge and experience with all budding and keen gardeners. Connect with Tammy on Instagram.


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