Best Liquid Fertilizer for Indoor Plants: According to my Tests

Are you searching for a liquid fertilizer for indoor plants? For those who are busy but love houseplants, I recommend a 3-1-2 ratio of a liquid NPK fertilizer (like 9-3-6) or a balanced liquid fertilizer such as 10-10-10 along with a seaweed-based fertilizer and Humic acid. However, you must spend more time reading this post to have lush plants with large stunning foliage or gorgeous flowers. So, keep reading.

Hi, I’m a horticultural consultant and would like to share my experiences on the best liquid fertilizer for houseplants. Before fertilizing, you must group your house plant collection into the three below groups. This is because every group has its own specific feeding program.

• Foliage Houseplants
• Flowering Indoor Plants
• Indoor Succulents and Cacti

And now, let’s find the best liquid fertilizers for your Houseplant collection.

Liquid Fertilizer for Indoor Plants: Various Types

 ➡ If you know enough about houseplants’ fertilizers, jump to the next to find the best feeding program for your houseplants, otherwise, this part can be helpful.

As you know, plant foods are a mixture of various nutrients. Based on how much a plant needs a nutrient, the nutrients are grouped into Macronutrients (plants need them in high amounts including N, P, K, Ca, Mg, and S) and Micronutrients (plants require them in low amounts however they play critical roles, they include Fe, Mn, Zn, B, Cu, Mo, Cl). various fertilizers have different patterns of nutrients.

In addition to nutrients, other substances such as Amino acids, sugars, and so on benefit houseplants and we use them as supplements in plants diet. In the following, you will get familiar with the most popular of them.

NPK Liquid Fertilizer for Indoor Plants

First, let’s get familiar with a broad-spectrum fertilizer: NPK. I am sure you’ve heard of its name.  NPK is the most common houseplant food in various ratios of three major nutrients:

• Nitrogen (N)
• Phosphorus (P)
• Potassium (K).

In this post, I‘ll focus on its liquid form, as a popular houseplant fertilizer.

Nitrogen (N), Phosphorus (P), and Potassium (K) are three important macronutrients in plants that are necessary for their growth and productivity and support overall plant health. They are the foundational nutrients of NPK fertilizers. Every NPK fertilizer has its specific ratio of these elements which is called based on it. For example, a 9-3-6 NPK have 9% N, 3% P, and 6% K.

To find the best liquid fertilizer for your houseplant, you must get familiar with these elements’ roles in your indoor plant:

• Nitrogen (N):

As you know, Proteins (Pr.) are the fundamental structures in living matters like your houseplant. Every protein is built of building blocks called Amino acids and Nitrogen is a key component of amino acids.

In addition, all biochemical reactions are facilitated and regulated by Enzymes which are a kind of Pr. So, your plant for healthy growth needs a high amount of Nitrogen to produce proteins and enzymes.

Nitrogen is also a critical element of Chlorophyll molecules (a plant factory for capturing sunlight energy by photosynthesis).

 ➡ Hence, Adding Nitrogen to plants means more N, more chlorophyll, more photosynthesis, more food, more Protein and enzymes, and more vegetative growth.

• Phosphorus (P):

Your plant (similar to other living matters) needs energy for its vegetative and reproductive growth. Your house plant gains the sun’s energy by photosynthesis in its leaves and transfers it to other parts like roots, buds, flowers, etc.

 ➡ Adenosine Triphosphate (ATP) is an “Energy currency” of plant cells. The energy produced by photosynthesis is stored inside the ATP. ATP transfers energy throughout the plant to use. Phosphorus is a critical element in ATP. So, plants’ vegetative and reproductive growth will be stopped in Phosphorus deficiency conditions.

➡ n addition, Phosphorus is a key element of DNA and RNA (the macromolecules that hold our genes). So, the plant cell division (the basic process of growth and reproduction) will slow down or stall in Phosphorus deficiency.

• Potassium (K):

Some gardeners call Potassium a “Quality nutrient“. Do you know why? Come on to tell you.

•  ➡ Potassium (K) is critical for necessary enzymes in the production of sugars and starches. Hence, K plays an important role in the taste and colore of fruits and flowers.
•  ➡ As I told you Nitrogen play a vital role in Photosynthesis. Potassium (K) can also boost Photosynthesis and raise the efficiency of Nitrogen.
•  ➡ It also facilitates the transfer of other nutrients and carbohydrates throughout your plant. Hence adding K to plant foods will increase their vegetative and reproductive growth.
•  ➡ Potassium is an important cellular osmotic regulator that causes the plant cells to stay turgid (firm and plump) and improves the absorption of nutrients. So, in K deficiency your plant becomes wilted.
•  ➡ Potassium also resists your plant against drought, cold weather, and diseases. Thanks to K.
•  ➡ It also promotes Sclerenchyma (a support tissue composed of hard woody cells) production in your houseplant stems. So, K fertilizers help your plant stems grow up easily.

Ratios of N, P, and K vary in different NPK fertilizers. Various house plants (including foliage plants, flowering plants, succulents and cacti) need specific ratios of NPK. It also can vary in their different life stages (vegetative or reproductive stages). In the following, I’ll give you more details.

Supplement Liquid Fertilizer for Indoor Plants

In addition to liquid NPK fertilizers, supplements such as Humic acid, Amino acids, and Seaweed-based fertilizers are complements in your indoor plant’s diet.

However, they often consider natural (organic) liquid fertilizers for houseplants but they are not complete fertilizers and must be used as supplements. So, you must know how and when to use them.

First, let’s get familiar with these plant supplement fertilizers and then I will give you a program to add them to your houseplant diet.

• Humic Acid Fertilizers

Some people think Humic acid is a single molecule but it is a complex mixture of organic molecules produced from the breakdown of plant and animal matter over many years. So, it is high in carbon and oxygen.

This magic dark brown or black substance is naturally found in soil, peat, oceans, and even freshwaters. It is extracted and turned into usable forms in agriculture. Its commercial forms can be solid or liquid. I think Humic acid is an important component of healthy soil because:

• Improve soil structure by promoting beneficial soil microbes and water retention
• Increase the nutrient availability for plants
• Suppress plant diseases.

 

• Amino Acid Fertilizers

As I told you before Amino acids are building blocks of proteins. Some are also signals that simulate specific functions in plants such as root growth or activation of plant defence mechanisms. Your plant uses a lot of N to produce amino acids.

Nowadays, breaking down plant proteins (such as fermented corn or hydrolyzed soy protein) into their amino acid components produces commercially available amino acid fertilizers. These amino acids can directly be absorbed by plant roots and leaves and provide:

• A readily available nitrogen source to plants.
• They enhanced the absorption of other nutrients such as Iron and zinc by acting as chelating agents.
• Some amino acids can also stimulate root growth, promoting more nutrient uptake. It can be very useful after repotting your houseplant.
• Some Amino acids in fertiliser can also simulate the plant defence mechanisms and help your plant against pests and disease.
• When you add an amino acid fertilizer to the soil, it is a delicious food for beneficial soil microbes living in the rhizosphere (around the roots). So, the beneficial microbes reward you by producing hormones that stimulate root growth, improving soil nutrient acquisitions and protecting roots against aggressive pathogens.

However, it is not a complete fertiliser (doesn’t contain all the plant’s essential nutrients), I strongly recommend using Amino acid fertilisers as the best supplements to resist your houseplant against environmental stresses such as repotting, drought, hot weather, pests and diseases.

People often ask me how to use Amino acids: soil drenching or leaf spraying? If you want a fast effect for example to encounter stress, spray it on leaves. But for a lasting effect, add it to the soil.

• Seaweed-Based Fertilizers

Seaweed-based fertilizers are one of the most popular organic liquid fertilizers for indoor plants. However, according to my tests, they should be considered supplements in your houseplant diet.

Seaweed-based fertilizers not only contain major elements (such as N, P, and K) and Micronutrients (like Fe, Zn, Mn, and B) but also offer a complex mix of beneficial compounds like ((such as Alginates, Betaines, Cytokinins, and Auxins) and Humic Substances (like Humic and Fulvic acids).

 

Some Important Seaweed-Based Fertilizers Compounds
Nutrients		Beneficial Compounds
Macro-	Micro-	Bioactive Compounds			Humic Substances
		Sugars	Amino Acids	Plant hormones
N, P, K, Mg	Fe, Zn, Mn, B	Alginates: Improve soil structure and water retention	Betaines: Helping plants tolerate stress conditions like drought and salinity	Cytokinins: · Cell division · Shoot growth · Delay leaves’ ageing	Humic acids	Fulvic acids
				Auxins: ·   Root development ·   Stem elongation

The overall benefits of Seaweed-based fertilizers:

• Improved Nutrient Uptake
• Enhanced Stress Tolerance
• Stimulated Growth and Development
• Improved Soil Health

Why do you consider Seaweed-based fertilizers as supplement fertilizers, not complete fertilizers?” people often ask me. These organic plant foods are derived from extracts of various seaweed species (brown alga, green alga, red alga, and so on). However various nutrients and beneficial compounds are in Seaweed-based fertilizers but vary depending on the seaweed source and processing methods. Hence, every fertilizer has its specific nutrient and compound profile and may not provide all the essential nutrients.

Brown algae have a higher amount of natural phytohormones, and micro and macro-nutrients than other types so, the most commercially Seaweed-based fertilizers are derived from it (like ‘Sargassum’, ‘Ascophyllumnodosum’, ‘Eckloniamaxima’ and ‘Laminaria japonica’).

I always recommend:

• Choosing a reputable brand
• Reading the label, find its nutrient profile, and attend to application recommendations.

Now, lets to find the best diet for your indoor plant collection. Based on your houseplant (foliage or flowering, Tropical or succulents, …), you must add various percentages of nutrients to them. keep reading to help you design a feeding program for your indoor plant with the best liquid fertilizers and supplements.

Best Liquid Fertilizer for Foliage Indoor Plants

Indoor plants such as Photos, Monstera, Philodendron, Dracaena, indoor palms, or Nerve plants are popular for their lovely foliage. All indoor gardeners try to encourage these plants to produce big lush leaves on strong long stems.

– Can you tell me which nutrients in your NPK fertilizers can help you more with this issue?

– Excellent, Nitrogen. N increases photosynthesis and vegetative growth of your houseplant. Hence, some indoor gardeners add fertilizers with a high N ratio to foliage houseplants.

However, High N will sensitive your plant to diseases and stresses. In addition, other nutrients such as Potassium (K) increase the N efficiency and Phosphorus is necessary for cell division and plant growth.

Additionally, K resists your plant from environmental stresses such as drought, cold weather, and diseases.

Hence you should use liquid NPK fertilizers such as 10-10-10 or 20-20-20. I also tested a 3-1-2 ratio of liquid NPK fertilizers (for example 9-3-6) and found it well for house plants especially when adding the above supplements to your plant diet.

I often recommend the bellow program for feeding the foliage indoor plants with liquid fertilizers: ·        Fertilizing with Humic acids (soil drench) ·         Two weeks later: Feeding with a liquid NPK fertilizer (10-10-10, 20-20-20, or a 3-1-2 ratio) (soil drench) ·         Two weeks later: Fertilizing with a seaweed-based fertilizer (spray leaves and soil drench) ·         Repeating this program during growth seasons. If your plant encounters stresses such as repotting, hot weather, etc., you can add an Amino acid fertilizer to the above program.

Best Liquid Fertilizer for Flowering Indoor Plants

People often ask me “What fertilizer makes Hoyas bloom?”. Houseplants such as Hoya, Peace Lily, or Birds in Paradis although have stunning foliage, we hope to prize us with their gorgeous blooms. Fertilizing is one of the factors involved in houseplants’ flowering (please note that it is “One of the Factors”).

For a “flowering houseplants” diet, you should consider a program that promotes lush foliage and encourages your plant to bloom.

High N Fertilizers will encourage your houseplant to produce big lush leaves while they will delay flowering. Please note that N is essential for reproductive stages, so, N deficiency conditions will hinder blooms too. The research shows that a low moderate level of N is critical for flowering (not a high level, not a deficiency).

Hence to encourage your houseplant to bloom, you should feed it with a low N ratio fertilizer such as 12-12-36 or 10-52-10. P will promote flowering due to its role in cell division and transferring energy to blooms. K improves the size and color of blooms.

Now, come on to make a good program for flowering indoor plants with liquid fertilizers:

Follow the diet recommended for foliage house plants in the previous part during the growth season. Consider the best time for flowering your houseplant, and replace the following diet to encourage it to flower. Please note that flowering takes a lot of energy from your potted plant, so, don’t do it frequently. ·         Fertilizing with Humic acids and a 10-52-10 liquid NPK fertilizer (soil drench). ·         Three weeks later: Fertilizing with a seaweed-based fertilizer (spray leaves and soil drench) ·         Three weeks later: Feeding with a 12-12-36 liquid NPK fertilizer (soil drench). ·         Repeating this program till flowering.

Best Liquid Fertilizer for Indoor Succulents and Cacti

Most people lose their lovely succulents and cacti because of overwatering or over-fertilizing; however, some kill them by under-watering or lack of fertilizing.

The first group doesn’t know the difference between succulents and cacti with other houseplants. These plants can store water in their leaves and hence don’t need much water. Additionally, over-fertilization, especially feeding them with high N fertilizers such as 20-20-20 will increase the risk of root rot and other diseases in succulents and cacti.

The second group believes the Succulents and Cacti don’t need fertilising because these plants thrive in poor soils in their natural habitat. It’s true but they confront a few pests and diseases in their natural habitat too, while various parasites, tiny bugs, and pathogens attack them in our house.

They also must cope with other stresses such as cold weather, overwatering, high humidity or heavy soils. As I told you before, proper fertilization will help your plant resist pests, diseases, and other stresses.

In addition, feeding them with some fertilizers encourages them to flower and add to your indoor décor beauty.

I recommend the bellow diet for feeding indoor Succulents and Cacti with liquid fertilizers: ·         Feeding with a 2-4-2 liquid NPK fertilizer (or a diluted 10-52-10) and Humic acid (soil drench) ·         Three weeks later: Fertilizing with a seaweed-based fertilizer (soil drench) ·         Three weeks later: Feeding with a diluted 12-12-36 liquid NPK fertilizer (soil drench) ·         Repeating this program during growth seasons. If your plant encounters stresses such as repotting, hot weather, etc., you can add an Amino acid fertilizer to the above program.

 

Conclusion

I gave you programs for feeding your various houseplants and now, you know how to choose a liquid fertilizer for your indoor plant. Please tell my readers and me about your experiences in feeding your houseplants and introduce fertilizers that you find well. You can also ask me your questions below this page.

Anyway, to find a special fertilizer for a particular houseplant (for example Pothos, Photinia, Monstera, Hoya, etc.) read my other post.