Fertilizer 101: Choosing the Right Fertilizer for Your Houseplants

Fertilizer 101

It's spring which means it's time for your plants to start exploding with growth! But how do you help them achieve their maximum potential for growth? Fertilizer, duh! But a lot of houseplant owners have no idea where to start when it comes to fertilizer. We're going to walk you through the science behind fertilizer, and which fertilizer to choose. 

Understanding NPK Values

Fertilizer is made up of three primary nutrients that are essential for plants to grow and maintain a strong structure. Nitrogen, phosphorus, and potassium are the nutrients in question. While a plant makes its own food from the sun, it still needs these nutrients from outside sources to supplement its photosynthesis. These nutrients are called the NPK value. You will see numbers listed as 10-10-10, 3-9-1, etc depending on the concentration by volume. 

Different NPK values are better for different plants. Lower numbers such as 2-2-2 will be much less concentrated, and less likely to have negative affects on your plants. The numbers may vary depending on the type of plant it is formulated for. Most houseplants follow a balanced formula (each number is the same such as a 2-2-2) or a 3-1-2 formula. NPK values with a higher second number tend to be better for outdoor plants, flowers, and gardens. 

Now we'll discuss the different parts of NPK, and what benefits each nutrient brings to your houseplants!


Nitrogen is the most important nutrient for all plants. It is a vital component in the process of photosynthesis. If you're looking for larger, more vibrant foliage on your plants, nitrogen will be your best friend. A higher concentration of nitrogen is great for most indoor plants, as they don't flower or bear fruit. If you give a flowering plant a high concentration of nitrogen, it may actually stop the flowering process.


Flowering plants absolutely love phosphorus. This nutrient boosts root growth as well as buds, flowers, and fruit. Tissue formation is fueled by phosphorus, and it will help your plants as they grow. 


If you want your plants to be strong and have the structural integrity to last a very long time, you're going to want to make sure to give them some potassium. This nutrient helps with catalyzing enzymes within the plant and protein synthesis. Better growth will result from the plant being able to have more efficient cellular operations. 

Types of Fertilizer

There are so many different fertilizers on the market, but which one to choose? The main two types of fertilizer are chemical or natural/organic. Both come in a variety of mediums: gradual, liquid, stakes, pellets, etc. Chemical and natural fertilizers both have their pros and cons.

Chemical Fertilizers

Fertilizers that are artificially synthesized tend to have higher concentrations of NPK. It's very common to have double digit numbers such as 20-20-20. Although it may sound appealing to have more nutrients for your plants, it can actually be it's undoing. Putting too many nutrients in your soil can cause "fertilizer burn". Your leaves may look like they've been bleached or looking unhealthy. We recommend always halving the recommended fertilizer dosage.

Another benefit of chemical fertilizers is that they're water soluble and almost instantly absorbed into the root system. Although this is a great quick boost, it doesn't do much to increase the overall, long-term health of your soil. The nutrients will not hang out in the soil to feed the micro-organisms like a natural fertilizer would.

Using chemical fertilizers in early spring works to help your plants leave their dormancy period with the quick burst of nutrients to start the growing season. 

Our Favorite Chemical Fertilizers


Jacks Classic All Purpose Fertilizer, 8-Ounce
NPK: 20-20-20 (dilute by at least half)

Natural/Organic Fertilizers

If you follow organic gardening, or like to lean towards sustainability, natural fertilizers are a great option. They are mostly derived from components such as worm castings, bat guano, crushed shellfish, kelp, fish, etc. Natural fertilizers tend to have lower NPK values, so they won't provide quite the immediate boost that a chemical fertilizer would. Due to the lower NPK, natural fertilizers are sometimes regarded as a soil amendment instead of a true fertilizer.

The main benefit of organic fertilizer is the part it plays in the microbiome of your soil. On top of NPK it will have other trace nutrients that will be added to the soil long term. Micro-organisms in the soil will consume these nutrients and help fortify the soil's longevity in terms of fertilization. Making sure to fertilize with organic fertilizer towards the fall will help keep your soil full of those nutrients over the winter.

Our Favorite Natural Fertilizers 

Espoma Indoor! Liquid Plant Food
NPK: 2-2-2

Joyful Plants Organic Powder Fertilizer
NPK: 3-1-2

Bonide Fish Fertilizer
NPK: 2-4-0

Espoma Organic Earthworm Castings


DIY/Food Based Fertilizers

There have been many tales of rice or pasta water, crushed eggshells, diluted coffee, etc being used as "fertilizers". These are not classified as true fertilizers because most do not contain NPK that can be consumed by plants. These options are better being utilized in a compost. This is due to food scraps not being broken down properly to create bio-available nutrients. Compost, compost tea, or aquarium water, however, are great options for DIY fertilizers. These options have had the nutrients broken down into a form plants will be able to absorb. 


No matter what fertilizer you select, your plants are going to thank you for it! Just remember to pick an NPK that matches your plants needs (flowering vs foliage). Our fertilizer series will continue next time with how to apply fertilizer. 

Leave a comment

Please note, comments must be approved before they are published