News

Indoor plants require nutrients through the process of fertilisation, especially during the Spring/Summer growing season to ensure healthy growth because potting mix nutrients deplete over time. Unlike outdoor plants, indoor plants can't access on-going nutrients from natural soil, decomposing organic matter or rainwater. They rely on the water, potting media and fertiliser we feed them. A balanced liquid NPK fertiliser replaced essential macro-nutrients (Nitrogen, Phosphorus and Potassium), encouraging lush growth of foliage, strong root systems and better pest and disease resistance.  

Why do indoor plants need fertilising? 

While fresh potting mix contains the nutrients your indoor plants need to grow, over time those nutrients are used up by the plant and washed out with regular watering. Unlike outdoor garden plants, indoor plants can't access naturally replenished nutrients from the soil. Therefore regular feeding of your indoor plants helps to replace the same 17 essential nutrients that outdoor plants require, just in smaller amounts. 

Regular feeding helps replace these nutrients, supporting healthy growth, stronger roots and vibrant foliage. The ideal frequent time is during Spring and Summer when plants are actively growing and then reduce feeding during Autumn and Winter, as they become dormant for the colder months.  

Without nutrients, your indoor plants may become stressed, weak and unable to produce new growth. This can leave them susceptible to a range of pests and diseases, affecting your plants even further.  

Understanding Macro-Nutrients: What is NPK? 

All plants require 17 essential nutrients, but there are three primary macro-nutrients known as NPK that are required in the largest amounts.   

Nitrogen (N) – Promotes healthy leaves and stems and lush growth. 

Phosphorus (P) - Supports strong root development and helps flowering 

Potassium (K) - Improves overall plant health and protects from pests and diseases 

Most indoor houseplants thrive on a balanced liquid fertiliser (eg/ 10-10-10 ratio) of NPK nutrients. Flowering indoor plants can benefit for a higher-phosphorous blend.  

The other 14 macro/micro-nutrients: Magnesium (Mg), Calcium (Ca), Sulfur (S), Iron (Fe), Boron (B), Zinc (Zn), Copper (Cu), Manganese (Mn), Molybdenum (Mo), Chlorine (Cl), Cobalt (Co), Nickel (Ni), Carbon (C), Hydrogen (H), Oxygen (O). 

How to spot nutrient deficiency in houseplants 

• Rapidly yellow leaves: lack of Nitrogen (N) 

• Yellow leaves with green veins: lack of Iron (Fe) or Magnesium (Mg) 

• Stunted growth: lack of consistent Nitrogen supply (N) 

• Weak stems and poor flowering: lack of Phosphorus (P) and Potassium (K) 

Common indoor plant pests 

• Mealybug: Small, soft white fluffy pests that feast on the soft new growth and hide where the petiole meets the stem of the plant. Multiple extremely quickly.  

  • Treatment: Remove with eco-oil spray or dip a cotton swab into rubbing alcohol and dab directly on the mealybug to kill. 

• Scale: There are multiple types of scale, including soft and hard bodied scale and can be brown, black or red.  

  • Treatment: Scale stick to the stems of plants and can be removed using eco-oil on a cloth and scraped off.  

• Fungus Gnats: Little flying bugs that breed their larvae in moist soil, larvae feed on the organic matter within the soil.  

  • Treatment: To remove, place sticky traps to catch the flying gnats and  reduce watering to kill larvae.  

• Spider mite: Microscopic pests that live on the underside of leaves, sucking the sap and creating mottling or discolouration on the leaves. In extreme infestations, webbing will be visible on the underside of leaves.  

  • Treatment: Isolate the plant, remove any severely affected leaves and spray down with neem oil.  

• Thrips: Adults are small and black, larvae are light yellow that eat away at the leaf surface, leaving discolouration on the leaves.  

  • Treatment: Prune heavily infested leaves, regularly spray insecticidal soap or neem oil to kill off each of the thrips as they emerge into the next stage of the lifecycle.  

What kind of fertiliser should you use? 

Use a balanced fertiliser (Equal parts NPK) for foliage plants, or a high-phosphorus fertiliser for flowering plants. 

Fertilisers come in a variety of application methods including: 

• Liquid fertiliser: optimal fertilising method for indoor plants as plants have immediate access to the nutrients after watering. 

• Foliar spray fertiliser: Ideal for plants that readily absorb nutrients through their leaves  

• Slow release fertiliser: Low maintenance fertilising method, providing consistent fertilising over a range of months.  

How do I fertilise my indoor plants?

Each fertiliser has it's own fertilising requirements, ensure to follow the directions on the label for the frequency and quantity to fertilise your indoor plants. This is to ensure you are not overfertilising, causing issues including scorched leaves or underfertilising resulting in stunted growth. 

How can I ensure my plants are taking up the fertiliser?

Nutrient uptake depends on the right balance of light and water. Plants need adequate light to photosynthesise, producing the energy needed for healthy roots and foliage. 

Both underwatering and overwatering can reduce nutrient uptake. Waterlogged soil limits oxygen around the roots, causing them to prioritise oxygen over absorbing nutrients. This weakens the plant and can lead to root rot, fungal growth and eventually plant death. 

Overall, fertilising your indoor plants is essential for maintaining a happy and health indoor plant. Balanced potting mix, regular watering and fertilizing correct pH, light and water can create healthy strong and thriving indoor plants. Nutrients can vary from plant variety to variety. With optimized growth you can get a healthy plant. 

Visit The Grow Centre for all your indoor plant care needs this Spring and Summer. 

FAQ's: 

How often should I fertilise my indoor plants? Indoor plants are generally recommended to be fertilised with liquid every 2-4 weeks during the growing period. Slow release fertiliser is product based. Each product will have their own stipulations on the best feeding schedule, so ensure to follow the directions closely. 

Can I over fertilise my indoor plants? Both indoor and outdoor plants can be affected by over fertilisation. In indoor plants, this looks like an excess amount of calcium build up in the form of crystallisation of salts at the top level of soil. If you see this, flush the soil thoroughly with just water to wash away excess mineral salts.  

Can I fertilise my indoor plants in Winter? We don't recommend fertilising your indoor plants during Winter as most plants enter a dormant phase. Plants slow down their growth and therefore do not require fertilisation to help growth. Fertilising in Winter can result in nutrient buildup and leading to fertiliser burn or root damage.  

How do I fertilise indoor plants grown in water? Use a diluted liquid fertiliser for plants that are grown in water.  

Need expert indoor plant advice? To keep your plants thriving all year around, visit your local The Grow Centre for expert advice and plant care products.