The Basics of Houseplant Fertilizer

Plants need to eat too! Don’t forget to pick up a well balanced fertilizer to ensure that your foliar friends grow to their fullest potential. 

Fertilizing your plants is a necessary step in plant parenthood, as it promotes bigger and faster growth, and in some plants can even encourage blooms!

What are the numbers on my fertilizer package?

  • Each fertilizer has its own “NPK” value. N, standing for nitrogen, P for phosphorus, and K for potassium. These are the three primary nutrients that are essential for healthy plant growth. Different brands and types and fertilizers may label their NPK value as 4-4-4, or 16-9-25, 0-0-22, etc. These combinations of numbers indicate what nutrient that specific fertilizer is rich in. It is best to choose fertilizers that match your plants specific needs, however for most houseplants, a good all purpose fertilizer will do wonders!


  • Nitrogen is essential for general plant growth as plants require nitrogen to create amino acids. These amino acids are needed to create plant proteins and other essential enzymes needed for plant growth. This can physically be seen through the growth of shoots and foliage, i.e vegetative growth 


  • Phosphorus is needed to convert the sun’s energy into food. It promotes healthy root growth, flowering, and is needed to form seeds. This is physically seen through strong roots, and flower/seed production. i.e reproductive growth.  


  • Potassium is needed to keep plants strong as it plays a huge role in photosynthesis and the transport of food, water, and other nutrients within the plant. Stems and leaves of the plants will feel firmer and will be less likely to wilt. 



When to fertilize?

  • Nutrients in your soil deplete over time, whether that be through plant uptake or through the water that drains through the pot. Each brand/type of fertilizer will indicate when to fertilize according to the instructions on the package.

Different kinds of fertilizer: 

  • There are several varieties of fertilizer as they can range from solid granules, water soluble powders, to liquid. There are endless types of fertilizer that can meet your specific needs, but these are the staples that we carry in the shop.


    • The main fertilizer we use at Mari’s Gardens locations is osmocote. It is made up of solid granules that slowly release fertilizer into the soil of your houseplant with every watering. The NPK is low but balanced (4-4-4) to ensure that you don’t over fertilize your plant while it gets the nutrients it needs. Sprinkle over the top layer of soil and mix into the first 1-3 inches. 
    • When to reapply: Reapply every 3-4 months or when you notice the granules shrivel or dissolve. You may also tell if it's time to reapply if there is a slight decline in plant growth. 


Joyful Dirt

  • Another popular fertilizer is made by the brand Joyful Dirt. It is an organic based houseplant fertilizer (not for use in organic food/crop production). It can be sprinkled directly around the base of the plant or dissolved in water (1 tbsp per ½ gallon) every month. It's NPK value is 9-1-5, so it focuses on slightly higher nitrogen and potassium levels. 


Air plant fertilizer 

    • The air plant fertilizer available at Mari’s Urban Garden is available in a liquid form and can be applied via spray bottle. Air plants are naturally found growing out of soil (i.e on trees), and therefore take up nutrients through their leaves via water. Its NPK value is 16-9-25, but the formula is very dilute in comparison to regular fertilizers. This NPK balance encourages strong growth and the ability to reproduce keiki air plants, and.   
    • When to apply: once a week, spray dry air plants 1-2 times.




Instant Plant Food

  • Instant plant food is a small batch fertilizer for those with minimal houseplants. Its NPK values are 4-3-6. Each tablet is water soluble and it can be reapplied once every 3-6 months. Just drop a single tablet in any size glass of water, let is dissolve completely, and water your plants thoroughly with the solution. Each tablet feeds one large plant or several small ones. 

Stop by the store to pick up some plant food for your new (or old) houseplant babies! 😊

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