Achieving that much-desired look of a lush, green oasis indoors means knowing how and when to feed your indoor plants. Surprisingly, more indoor plants die from too much care than from neglect. Indoor plant care is really about learning to the right balance of plant food without supplying more than needed.

Indoor plants only need fertiliser when they are actively growing. When plants are kept indoors in low light conditions, they are not getting enough energy from sunlight to photosynthesise, which is the process that promotes the energy plants need to grow. Active growth only occurs when plants are growing in bright light and conditions are warm (eg. in spring and summer). Signs of active growth include the formation of new leaves, shoots or branches, and the appearance of buds and flowers on flowering indoor plants. If you've noticed these signs, it's time to get into a feeding regimen to help your plant sustain its development.

This Spathiphyllum is showing signs of new growth, which means it's time to get into a feeding regimen.

All about fertilisers

Fertilisers contain nutrients that help fuel growth. The most important of these are nitrogen (represented on the label by the chemical symbol N), phosphorus (P) and potassium (K). Find out more about each of these essential elements here. Different plants need different amounts of N, P and K, so an indoor plant-specific formula will yield the best results. You can find plenty of fantastic fertiliser options here.

While all types of plant food can be used (see our guide below), the easiest and most versatile formulations for indoor plant care are liquid or soluble. These allow you the option to apply nutrients directly to the foliage as a spray, or water onto potting mix to feed the roots. Plants under stress often better absorb nutrients through their leaves than their roots, so spraying onto foliage is also a good way to apply a plant tonic. 

 

How often to fertilise indoor plants

It's not always true that "more is better". It's definitely possible to overfeed your indoor plants, which can cause damage. Signs of over-fertilising include leaf burn (browning of leaves often around the leaf edge), residue on the outside of the container and plant death. Excess nutrients can also be washed out of the potting mix when watering. Not only does this mean that they're wasted, they may harm the environment if they enter drains and waterways.

Where plants aren’t in active growth they benefit from regular applications of a plant tonic (such as seaweed-based products), which contain no or little fertiliser. Hold off on applying a fertiliser until you move the plant into brighter light and it shows signs of growth. If it is possible to give indoor plants a spell outdoors, this is the best time to feed them. Apply plant food slowly initially as you move the plant into a more brightly lit position. Follow this up with a liquid feed every 10-14 days while they are growing. Always follow the recommended rates on the fertiliser container to avoid over-fertilising.

 

 

The best fertiliser for indoor plants

Not sure which fertiliser option is best for you? Have a read through our guide below and learn the differences between these formulations.

Liquid or soluble

These formulations are easy to use and apply - ideal for indoor plant care. Whether a soluble powder or a liquid formula, simply dilute in a watering can following the label instructions and water over the plants and potting mix. Apply regularly while plants are actively growing. A great example of this fertiliser type is Osmocote Pour & Feed House Plant Food.

Foliar spray

A foliar spray fertiliser can be a great option for your indoor plants. These tend to be weaker in concentration than one you'd water onto the soil, so as to avoid burning or damaging the delicate foliage - meaning they can be used more often and misted as generously as needed onto your plant. As an added bonus, spraying these liquids onto your plants' foliage helps boost the humidity around them, making for happier plants. For for a ready-to-use spray formula that will give your plants all the nutrients it needs, we recommend Living Trends Indoor Plant Food or Munash Indoor Foliage Spray.

 

Slow-release granular

Granular fertilisers offer a clean, no-mess way to apply fertiliser to plants. The small balls of fertiliser in a slow-release formulation break down very slowly, gradually supplying nutrients to the plant. These formulations are ideal for a long-term indoor plant that is growing, flowering or producing new foliage. One application lasts for many months. Apply it when repotting (unless the potting mix already contains fertiliser) and top up in spring or early summer. If you're after a great granular fertiliser, try Osmocote Plus Trace Elements Pots Planters & Indoors.

Plant tonics

While not actually fertilisers, these contain a mix of organic compounds and trace elements (from materials such as seaweed and rock minerals) and are formulated as a liquid to dilute and water on, or as a foliage spray to apply directly to the leaves. Use regularly to help combat the stresses of life indoors. Combine with a liquid, slow-release or foliar fertiliser to feed the plant when it is in active growth. For an excellent tonic, try Amgrow Seaweed Solution.