Blog Indoor Plants What Is The Best Fertilizer For Indoor Plants

What is the Best Fertilizer for Indoor Plants | Greg

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Kiersten Rankel
Dec 30, 2021

What is the Best Fertilizer for Indoor Plants?

Most potting soils come with ample nutrients which plants use to produce new growth. By the time your plant has depleted the nutrients in its soil it’s likely grown enough to need a larger pot anyway. To replenish this plant's nutrients, repot your plant in new soil after it doubles in size or once a year—whichever comes first.

You already know that your outdoor plants need a good fertilizer on occasion. Yes, they get all the goodies that nature provides, but they still require a little help once in a while to ensure they are being well-fed.

Your indoor plants need that extra boost of nutrition even more, because they don’t have the benefits of nature and the outdoors. They are a bit like children––what you feed them is what they get! 

Keep in mind that when you pot your plants in good, fresh potting soil and in a new pot, you may not need to add fertilizer right away. Some of them may even have fertilizer mixed into the formula. 

However, eventually you will definitely have to give your plant a good fertilizer at some point, so that it gets steady nutrition and can grow to its full stature. When that day comes, you obviously want to choose the best fertilizer you can to suit your plant’s needs. 🌱🌱🌱

Photo by Taylorgrace

Considerations Before Choosing Fertilizers

There are two things you should keep in mind before you select a fertilizer for your indoor plant.

Type of Plant 

Finding the best fertilizer for your indoor plants depends largely on the type of plants you have. For example, with flowering plants, you may require a phosphorus-rich fertilizer. Whereas a non-flowering plant may require more nitrogen instead. Or if you use grow lights for your plants, ensure you choose a fertilizer that will thrive under your lights. Always choose a fertilizer that is beneficial for the specific types of plants you plan to keep indoors. 

If you’re looking for more information on using grow lights, check out our latest blog on How to Use Grow Lights for Indoor Plants! 

Type of Soil 

The type of soil or potting mix you have is also a big consideration when choosing a fertilizer for your indoor plants. In many cases, you might already be using a potting mix that’s designed for your plants and that already contains the ingredients it needs. 

If so, you may not need any fertilizer for a while, or you might want to add fertilizer as an added bonus to give you plant a little extra nutrition.

Photo by Voidbugz

What is Fertilizer?

Most fertilizers contain the same basic ingredients that are essential for the healthy growth of plant-life. Most fertilizers include several different macronutrients needed for your plants to thrive. 


Nitrogen is essential for plant health and growth because it is an essential element of chlorophyll. Chlorophyll is used by plants to convert sunlight into food through the process of photosynthesis. 

Without enough nitrogen, plants won’t have enough chlorophyll for photosynthesis. Additionally, nitrogen is present in amino acids, which are the building blocks of protein in all living things. An indoor plant may need nitrogen to boost photosynthesis for it to flourish and remain healthy.


Potassium in plants is responsible for the regulation of water, ensuring it flows through the whole plant. All the other nutrients also travel with water throughout the plant. Potassium makes sure that the plant roots are well-formed and sturdy enough to support the plant’s life.

Potassium also plays a role in the production of proteins, starch and ATP in plants. Having enough potassium in their system makes plants more resistant to drought-like conditions. Meanwhile, a lack of potassium could lead to symptoms of dehydration.

Photo by ​​Steeze365daily


Like nitrogen, phosphorus is essential for the process of photosynthesis in plants––it helps convert the sun’s energy into food and channels it into the development of new cells and tissues. It helps promote root growth and development, and indirectly affects how much nutrients the plant can access and regulate. 

Phosphorus also makes the plant strong and resistant to cold weather conditions and stimulates tillering. Without enough phosphorus, plants may not be able to bloom as much. Since you want your indoor house plants to bloom heartily, it’s important to make sure your fertilizer has enough phosphorus for your plant’s needs.

Looking for detailed, step-by-step instructions on watering your plants? By using physics and machine learning to predict the water needs of any plant in any environment, the Greg plant care app will help you grow a healthy plant with confidence. Download the app today! 🌵🌵🌵

Additional Fertilizer Ingredients

High quality fertilizers may be formulated with a few additional ingredients. 


Unlike nitrogen and phosphorus, which are just components of chlorophyll, magnesium is the central element of chlorophyll in plants. Without magnesium, plants simply don’t have any chlorophyll available to stimulate photosynthesis and grow. 


Boron is vital for plants because of its role in the formation and strengthening of cell walls and in supporting the structural integrity of membranes. It also works to regulate the flow of energy into the growing parts of plants. 


Manganese has a direct effect on the metabolism of plant cells. It is essential for the optimal working of various vital processes in plants, including photosynthesis, cell growth, and respiration. 

It is also helpful in developing root resistance to pathogenic infections which may result in root rot, the development and elongation of root cells, as well as pollen germination. 

You may also find fertilizers that are specially designed to meet the nutritional requirements of a specific plant. Keep in mind that fertilizers like these will contain the optimum amount of nutrients that particular plant requires, and may not be suitable for use with other types of indoor plants. 

Our Favorite Types of Fertilizers

Slow-Release Fertilizer

Slow-release fertilizers usually come in the form of pellets or capsules that release their nutrients in the soil gradually, over time. The fertilizer pellets come in varying degrees of thickness, so that they dissolve at different time intervals and not all at once. 

Once you add in this kind of fertilizer, you can rest easy knowing your plant will get the nourishment it needs for quite some time! The nutrition delivered through each application of a slow-release fertilizer can last anywhere from 4 to 9 months. 

Due to the reliability and convenience factor of slow-release fertilizers, they have quickly become a fan favorite with many gardeners. However, once disadvantage of slow-release fertilizers is that you can’t control the exact amount of fertilizer that’s provided to the soil. Regardless, slow-release fertilizers are an ideal choice for small indoor plants placed throughout your home. 

Photo by Cassandra

Liquid Fertilizer 

Liquid fertilizers provide an easy way of enriching the soil with nutrients. These fertilizers are mixed into water and applied via a watering can. The frequency and intensity of liquid fertilization depends on the plants nutritional requirements; larger plants may need more, while smaller plants may need less. 

The advantage of using liquid fertilizers is that you can suspend the fertilization whenever you need. For example, suspending it in the winter months while growth is dormant, or speeding it up during the growing season. 

Liquid fertilizers make for easy application and allow you to control the intensity and dilution level of the fertilizer. You can choose exactly when and how much of it to apply. However, knowing how much fertilizer your plant needs can be a challenge, especially if you’re a beginner. That’s part of why we created the Greg App! 

Additionally, if you only have a few houseplants, you may end up throwing away or discarding a lot of liquid fertilizer because a small amount of fertilizer can make around a gallon of plant food. Not to mention you have to remember when to apply the liquid fertilizer. With both the pros and cons considered, liquid fertilizers still make a great choice for indoor plants. 

Granular Fertilizer

As the name suggests, granular fertilizers come with the grainy structure of pure fertilizer that’s thoroughly mixed into the soil. When the plant is watered, the liquid prompts the granules to release their nutrients into the soil all at once. 

However, just like with slow-release fertilizers, it’s not possible to control the level of fertilization when using this type of fertilizer. That said, granular fertilizers are best suited for repotting large plants and may not be the best choice for fertilizing any indoor plants. 

Organic Fertilizer

Organic fertilizers provide a sustainable and eco-friendly way of nourishing your plants, with minimal risks of damage to the plant itself. Since these fertilizers are made from natural ingredients, there is a smaller chance of harming the roots due to chemical exposure. 

Organic fertilizers can come in any form, including liquid, granular, and slow-release capsules. The nice thing about organic fertilizers is that they can be used for both indoor and outdoor house plants, depending upon your needs.

The best fertilizer for indoor plants is the one that is best suited for your specific plant-life. However we know that learning how to fertilize your indoor plants appropriately can take some time and require a bit of research. 

That’s exactly why we created Greg app, to help remove some of that guesswork in caring for your plants! We try to make tending your plants as fun and stress-free as possible. At the end of the day, gardening and caring for your plants––be they indoor or outdoor––should be an enjoyable and relaxing hobby.

Looking for more information on plant care? Check out our latest blogs on How to Repot Indoor Plants, Safe Plants for Dogs and Cats and How to Get Rid of Spider Mites on Indoor Plants. 🌾🌾🌾