9 Best Indoor Plant Fertilizers | How and When to Use

We all want our houseplants to be healthy and gorgeous. What often keeps us from achieving that, is the misconception that indoor plant care is a one-size-fits-all deal. Unless you’ve strategically chosen plants that have identical care needs. 

I’m not that studious, I’m a sucker for a pretty houseplant, regardless of care level. So if you’re like me, watering and fertilizing needs will vary among your houseplants.

So, how do you ensure proper nutrition for them all, without breaking the bank? I’ll tell you. It’s by discovering the best and most versatile indoor plant fertilizer.

Fertilizers for Indoor Plants 

My top nine fertilizer picks, for the most commonly grown houseplants, are just a quick read away. But, if you need fast, reliable recommendations for the best indoor fertilizer, here are my top three. 

Miracle-Gro Indoor Plant Food (Liquid) 1-1-1 

Best Indoor Plant Food

Miracle-Gro Indoor Plant Food (Liquid) 1-1-1 

Fast-acting, pump fertilizer that couldn’t be easier to use. Gentle and effective on all houseplant varieties, simply pump directly onto the soil.

Jobe's Indoor Houseplant Fertilizer Spikes 13-4-5 

Best Fertilizer Spikes for Houseplants

Jobe’s Indoor Houseplant Fertilizer Spikes 13-4-5 

Long-lasting, easy-to-apply nutrition for non-flowering houseplants with higher nitrogen for large, vibrant foliage and a strong root system. 

Neptune's Harvest Fish & Seaweed Fertilizer 2-3-1 

Best Organic Indoor Plant Fertilizer

Neptune’s Harvest Fish & Seaweed Fertilizer 2-3-1 

OMRI-certified, organic fish and seaweed liquid concentrate that ensures that foliage stems and roots will experience hardy growth resistance to pests.  

Choosing the Best Fertilizers for Houseplants 

Whether you have two houseplants or twenty, it’s always best to choose a fertilizer that’s both efficient and cost-effective. This starts with knowing what your plants need. 

Some plants, like ferns and tropicals, are sensitive to fertilizer. Fertilize these sparingly with a very gentle NPK. Slow-release options work best for these. 

Others, like orchids and Ficus varieties, are heavy feeders. The best indoor plant fertilizer for these will have a higher NPK ratio.

Flowering plants will require an NPK with more phosphorus and potassium to support bud production. Non-flowering plants will need more nitrogen. 

But, don’t worry about needing to buy 15 different kinds of fertilizer. My top picks are for all plant types, with the option to increase or decrease the dosage when needed. 

Houseplant Fertilizer N-P-K Ratio 

If you’re going to pick one NPK, I would recommend a gentle, well-balanced one. I use a 4-4-4 on everything from my fern collection to my ornamental fig trees. I just alter the dosage and application frequency. 

For flowering plants, I just add a little extra phosphorus and potassium using organic sources, which we’ll cover in a moment. 

But first, let’s start with the basics. What is an NPK and what does it do?

A fertilizer NPK is a three-numbered formula that represents that product’s macronutrient ratio. For example: A 4-4-4 NPK contains 4% Nitrogen (N), 4% phosphorus (P) and 4% potassium (K). All plants require these elements in order to thrive, just in different proportions. 

Indoor Plant Soil pH and Nutrient Uptake 

If, after months of careful fertilization, your plants are still not thriving, it may be your soil pH.

Soil pH indicates its acidity or alkalinity. The pH scale runs from 1-14, with 7 being neutral. A pH lower than 7 is considered acidic, higher and it’s alkaline. Most houseplants prefer soil with a 6.0-7.0 pH.

Why is this important? 

Below 6.0, nutrients flood the soil, resulting in over-absorption and potential root burn. Above 7.0, nutrients become locked in the soil and unavailable to roots. 

Managing soil pH is as easy as adding sulfur to lower it or powdered limestone to increase it. Measuring pH can be accomplished with easy-to-use pH test strips. 

Granular Vs Liquid Fertilizer 

Granular fertilizers are often preferred over those that tend to inundate plants all at once. A slow and steady stream of nutrients gives your plants plenty of time to absorb, process, and benefit from them.

Being fast-acting, you’ll see more immediate results with liquids. They can also be mixed with other organic elements (like extra phosphorus and potassium for your flowering plants) where dry granules can’t.

Another difference is how often you need to apply them. Granules are applied once and release nutrients with every watering. This can last for several months, depending on the brand.

Whereas, liquids often need to be diluted with water and applied every week. 

Liquid Fertilizer for Indoor Plants 

Over time, indoor potting soil loses much of its inherent nutrient base, due to leaching from frequent watering. If you don’t typically fertilize your houseplants, this may result in a visible deficiency.

Liquids provide an immediate remedy to that deficiency. Some brands can be used as both soil drenches and foliar sprays. In my experience, these work really well when large-leaved plants or indoor trees are experiencing chlorosis (yellowing of foliage).

However, caution is recommended. Accidental over-feeding is common and could lead to root burn. 

Slow Release Fertilizer Granules for Houseplants 

Granule fertilizers are water-soluble materials covered in a semi-water insoluble coating. Resulting in a slow conveyance of nutrients. 

The thickness of this coating varies from brand to brand and some include sulfur if you need to lower your soil pH.

Granules are an efficient slow-release choice that allows you more flexibility in the feeding process. For example, based on a particular plant’s performance, you can apply less or more than the recommended dosage, as needed.

Some are also water-soluble, changing it to a quick-release if your plant seems to need nutrients faster.  

Fertilizer Spikes 

Spikes are one of the most convenient options to use, especially if you have a lot of houseplants. Pre-measured in various sizes, they’re easy to push into loamy soil and release nutrients with every watering. 

Being slow-releasing, they offer the same long-term benefit as granules and also run little risk of plant burn or run-off. As a result, spikes are considered an “eco-friendly” fertilizing option, despite, in some cases, being inorganic.

With consistent nutrient access comes the added benefit of increased resistance to disease and pests. Unused portions can be stored mess-free until needed.  

Synthetic Vs Organic Indoor Plant Fertilizers 

When deciding between an organic or synthetic fertilizer, consider your gardening style, goals, application preference, and end-result expectations. 

In addition, a basic understanding of how each works and affects your environment can help support an informed decision.

Organic fertilizers:

  • Typically plant or animal-based
  • Contain moderate levels of nutrients, similar to what plants would get in the wild
  • Can nourish tender houseplants for longer periods of time
  • Can improve soil fertility with little risk of contamination

Inorganic fertilizers:

  • Are mass-produced using minerals and synthetic chemicals
  • This can result in more lush foliage and a higher number of buds on flowering plants
  • But, these can damage the natural makeup of the soil, in the long term.

DIY Indoor Plant Fertilizer 

As I mentioned, I’ll occasionally pull something from my kitchen compost bin or pantry to add to my flowering houseplants that need an extra boost of potassium and phosphorus for bud production. 

Lots of left-over recipe ingredients are great sources of nitrogen, too. These are perfect for non-flowering plants that need a natural pick-me-up. Put the right combination of these together and you have FREE houseplant fertilizer! Okay, it can be a bit messy and potentially smelly taking this approach to feeding your plants, but it’s an option if you have an interest in it in-house so to speak!

Here are some common kitchen scraps that can give your houseplants a natural lift:

  • Crushed eggshells (Increase pH and add calcium)
  • Banana peels (Potassium)
  • Used coffee grounds (Nitrogen)
  • Green tea (Lowers pH)
  • Molasses (Carbon, iron, sulfur)
  • Epsom Salts (Magnesium and sulfur)
  • Wood ashes (Increases pH)
  • Gelatin powder (Nitrogen)
  • Corn gluten meal (Nitrogen) 

Best Indoor Plant Fertilizer Reviews 

To find the absolute best indoor plant fertilizers for your lovely greenery, I’ve conducted some in-depth testing. The results of which I’d like to share with you.

These include specific product details and the pros and cons of each to allow you an informed decision. Below are the nine market choices that came out on top, as the cream of the crop. Based on performance, versatility, and ease of use. 

Pros

  • Easy-to-use pump action bottle
  • NPK gentle enough for all houseplants

Cons

  • Pouring directly from the bottle may result in fertilizer burn 

This fast-acting fertilizer couldn’t be easier to use. Gentle and effective on all houseplant varieties, simply apply the recommended dosage, per pot diameter, directly onto the soil, then water normally. Feed once a week and your houseplants will be healthy and continually nourished.

If you need to water several plants at once, you can make it even easier by adding a few pumps (as recommended on the label) to a watering can.

This mild NPK is formulated to nourish even the most sensitive houseplants. My ferns and tropicals responded surprisingly well. Yet, it was versatile enough to satisfy my propagated aloe veras and flowering cacti.

Unlike previous versions, this new formula doesn’t foam up. It sinks through the soil, straight to the roots.

How To Use: Apply 2 pumps for small pots and 5 pumps for larger pots (over 6″ diameter), then water normally. Or, mix into a watering can. Repeat weekly.

Pros

  • Slow-releasing for healthy, gradual improvement of ailing plants.
  • Higher nitrogen content promotes vibrant color and strong roots.

Cons

  • Best suited to non-flowering houseplants

If pale plants are a problem, Jobe’s indoor houseplant spikes contain a generous amount of nitrogen for increased chlorophyll production. Vibrant green plants will result and variegated plants will produce clearer and more distinct patterns. All at a speed that is designed for optimum benefit.

I put these in the soil around a couple of large peace lilies in my sunroom. I was concerned that these would stimulate an abundance of leaves but no flowers. I was so wrong. The 4% phosphorus and 5% potassium were all my lilies needed to beautifully bud. 

This 50-pack from Jobe’s is one of the best value-for-money options on this list. 50 spikes per pack, each lasting for eight weeks, means you could fertilize a house full of plants for just pennies.

How To Use: Just push new spikes into the soil every 8 weeks. Then, water well to activate.

Pros

  • A mix of nutrients from both fish and kelp
  • Organic results without harmful chemicals

Cons

  • The smell may seem strong when used indoors in high doses

This OMRI-certified, organic fish and seaweed concentrate provides a gentle combination of macro and micronutrients for all houseplants. The higher phosphorus content especially improved my Christmas cactus, which didn’t bloom at all the previous year.

The hydrolyzed formulation means essential fish and seaweed oils and proteins are left intact for maximum benefit. Macro and micronutrients, plus trace elements and naturally occurring enzymes, stimulate healthy growth. 

This can also be used, organically and effectively, to combat leaf chlorosis on plants in nitrogen-poor soil.

The best part is, that this fertilizer option isn’t limited to just houseplants. You can take this out into the garden and use it there, to increase the budding of all your annuals, perennials, and flowering vegetables.

How To Use: Indoor plants – Use 1 tablespoon per gallon of water, every 1-2 weeks. Outdoors –  Use 1/8 Cup (1 fl. oz.) per gallon of water, every 1-2 weeks.

Pros

  • Easy to use on many different tropical bloomers
  • Eco-friendly with very little risk of overfeeding or root burn

Cons

  • A slightly higher price than other fertilizers on the market 

I am a big fan of these organic, potassium-rich capsules from Earth Pods. With no measuring or smell, you just pop the recommended number of concentrated, time-release caps into the soil around your houseplants for vigorous root growth and leaf formation.  What could be easier?

The vivid color you get on African violets, primrose, amaryllis, poinsettias, and begonias is first-rate. This is another one of my picks where its use is highly beneficial for outdoor, container plants, as well.

Ground-planted ferns, and other light feeders in my shade garden, are susceptible to over-fertilizing. Placing one or two of these (depending on plant size) worked wonders without overwhelming them.

How To Use: Insert capsules, containing organic macro and micronutrients into the soil near the base of the plant, then water normally. Repeat every 14 days for best results. 

Pros

  • Feeds for up to 6 months
  • No risk of root burn

Cons

  • Tiny resin pellets may be visible once nutrients have been delivered 

These patented, smart-release granules are best used for large, heavy-feeding houseplants. Out in the garden, this NPK will invigorate foliage color and increase flower production. 

High nitrogen and potassium content, plus supporting phosphorus and eleven essential minerals, are gradually introduced into the soil. Feeding for up to 4 months, while encouraging strong root growth and an increased tolerance for low light and drought.

Nutrients are gradually released as the surrounding temperature warms up. In summer, this coincides with the active growing stages of outdoor and indoor plants. In winter, a warmer indoor environment will trigger nutrient release for houseplants. When used as directed, there is little risk of root burn.

How to use: As a soluble, sprinkle 1 scoopful of feed per 2 gallons (8 liters) of water for every 4 square feet of the plant. For a slow-release application, mix the recommended amount into the top 1-3 inches of potting soil. Then water regularly.

Pros

  • Slow-releasing for gradual and prolonged nutrition
  • Lasts for a full 30 days

Cons

  • Several, per plant, may be required. Depending on pot diameter. 

These fertilizer spikes are just as easy to apply as my Jobe’s spike pick. Yet, given the phosphorus-heavy NPK here, I would strongly recommend these for small or newly-propagated plants that could use a strong boost toward forming robust root systems, stalks, and stems. As well as, plants that are ailing or yellowing due to a nutrient deficiency. 

This covers care for both flowering and foliage houseplants with the inclusion of superphosphate, magnesium sulfate, potassium sulfate, and boric acid. Zinc, copper, and iron round out this effective formula. 

This combination of nutrients will also stimulate new growth and a hastened maturity in spring, and outdoor annuals in pots. Faster maturity means a longer bloom time on healthy and vigorously growing plants.

How To Use: Simply insert the suggested number of spikes (per pot diameter) just beneath the soil level. Re-apply spikes every 60 days in spring and summer, every 90 days in winter and fall, if necessary.

Pros

  • Effective combination of nutrients and pest control
  • Removed the risk of unpleasant fumes from spraying insecticides in the home

Cons

  • Maybe at a slightly higher price point than other fertilizers 

How often have you found little white, green, brown, or black bugs flying around your houseplants? These pests are attracted to them for a number of different reasons, depending on the species. But, typically, you’ll see these taking up residence on plants that are insufficiently watered or fertilized.

These tiny, slow-release capsules from BioAdvanced are specially formulated to provide optimal nutrition for indoor and outdoor potted plants. While protecting against and eliminating pests. These include aphids, whiteflies, leafhoppers, mealybugs, and more, with no toxic spraying required.

The package comes with a convenient capsule applicator. But, a chopstick, orchid stick, or any other long, slim tool (including your pinky finger) will work, just fine. 

How To Use: Make a hole large enough to place one capsule into, then push it down into soil just below surface level. Then, water normally. Your potted plant is protected and nourished for up to 2 months. 

Pros

  • Millions of beneficial microbes for optimum plant health.
  • Organic results without harmful chemicals

Cons

  • It May carry an earthy odor 

If you’re an organic gardener and prefer liquid options, this Espoma version is just as gentle as the first, synthetic option from MiracleGro. Yet, with purely organic ingredients.

This fertilizer doesn’t just nourish your plants. It increases soil fertility and resistance to pests and disease. Wholesome nutrition is released with no chemicals, fillers, or sludges.

And being a liquid, it’s fast-acting on a wide range of houseplants. From delicate, light feeders all the way up to large, indoor ficus trees with big appetites.

What makes this so effective? Kelp extracts, humic acids, and a proprietary set of beneficial microbes to ensure optimal results.

How To Use: Shake well prior to mixing with water. The bottle even pre-measures the dose for you. Simply close the lid, turn the bottle upside down, and then right-side up. Flip the lid open, pour the contents of the Easy Dose cap into your watering can, and add 1 quart of lukewarm water. 

Pros

  • Formulated for both hydroponic and soil-grown plants
  • Patented, organic pH buffering system great for all hydroponic applications

Cons

  • Plant damage may result if overapplied 

Do you enjoy starting new indoor flowering plants from seeds? Or, perhaps, you live in a colder climate and you seed spring annuals indoors. Better yet, you took the leap and started your own hydroponic garden. If any of these sound familiar, then this final pick is just for you.

This nutrient-packed NPK from AeroGarden is designed to work as an organic pH buffering system for all hydroponic applications. But, gentle enough to stimulate incredible growth in soil-grown plants, as well. 

The patented recipe in this little bottle packs a punch with a combination of basic plant nutrients (ammonium nitrate, potassium nitrate, potassium phosphate) and minerals (calcium nitrate and magnesium) that ensures a quick release by way of clean, filtered water.

How To Use: For hydroponic applications: 2 capfuls/liter for the first and second applications. Then, three capfuls every 2 weeks, thereafter. For houseplants: mix 2mL per gallon of water and apply weekly. 

How to Fertilize Indoor Potted Plants 

How to apply the best indoor fertilizer options we’ve discussed will depend on their application method. Liquids are applied by watering the can or spraying right onto the soil.

These should be applied in the cooler hours of the day, to prevent scorching on foliage and flowers of plants that prefer direct sun.

Diluting a nutrient-rich concentrate (Neptune’s Harvest or Espoma Indoor!) and applying the resulting ‘tea’ can give you more control over the dosage and frequency of feeding for a wide range of houseplant species.

Dry granules, spikes, and capsules can be applied any time of day or night. With only some requiring watering in. Osmocote Smart-Release  Granules can be added as a top dressing or worked into the soil. Spikes and capsules (EarthPods Premium or Jobe’s 50-pack) are simply inserted into loamy soil and watered in to activate. Reapplication of these ranges from 2-4 months. 

Avoiding Fertilizer Burn 

Indoor plants are only equipped to absorb and process so much fertilizer. How can you tell if a houseplant has been over-fertilized? Anyone of the following symptoms (or a combination of several) will be visible:

  • Decreased or stunted growth
  • flimsy stems and stalks
  • an increased vulnerability to pests and disease
  • burned or dried leaf margins
  • yellowing of the leaves.
  • The collapse of the main trunk or stalk
  • Plant death  

Fertilizer burn happens when high concentrations of fertilizer salts draw too much moisture from your plant’s root system, causing severe and sudden dehydration. 

Preventing fertilizer burn starts with following the package instructions carefully. Fertilizing only during periods of active growth and cutting the dosage for sensitive plants, will make it easier to avoid fertilizer burn.

When to Fertilize Houseplants 

Just like outdoor plants, indoor varieties also experience seasonal dormancy. When their metabolic processes slow way down, in order to conserve energy, during periods of limited sunlight. 

At this time, even in temperate climates, they don’t require fertilizer, nor can they actually use it. It’s important to know how and when to feed these particular plants and how to help them rouse from dormancy.

Start fertilizing these roughly 8 weeks (using ½ the recommended dose) before the last expected spring frost. Or, in warm climates, when temperatures remain about 72°F.

Even though they’re indoor plants, these are good indicators that sunlight is increasing and waking houseplants into active growth. As summer begins, start the full recommended dose and frequency.

About 2 months before the first expected autumn frost, it’s time to start weaning your plants off of fertilizer by returning to half the dosage and frequency. 

When to Start Fertilizing Houseplants 

If you’ve never fertilized your houseplants before, it helps to remember that even plants and trees, growing in the wild, get fertilized through the recycling of fallen, natural materials around them. 

Also, remember that fresh potting soil with added nutrients will lose its luster, over time. As plants absorb and utilize what it has to offer. 

You’ll know if fertilizer is needed by observing your plant’s behavior. There are certain telltale signs that will indicate a general or specific nutrient deficiency.

  • Yellow leaves (chlorosis)
  • Yellow or brown leaf edges
  • Holes in leaves
  • Leaves have a purple or red tone
  • Yellowing between leaf veins
  • Small or malformed leaves
  • Yellow or brown spots on leaves

How Often to Fertilize Indoor Plants 

How often to fertilize the various plants in your collection will be dictated by the brand and application method you choose. Liquids need to be applied more often, due to their fast-acting nature and the leaching that occurs with frequent watering. 

Granules, spikes, and capsules are slow-releasing and less likely to reach out, resulting in fewer applications needed.

For example, Miracle-Gro’s indoor plant food spray needs to be reapplied every week with regular watering. As does AeroGarden’s hydroponic formula. 

Yet, MiracleGro’s spike option and the dual-action capsules from BioAdvanced only need to be replenished every two months. 

Regardless of which brand you choose, label directions should always be followed to ensure that no damage is caused by accidental over-fertilizing. 

Fertilizing Indoor Plants in Winter 

I mentioned that houseplants, in most hardiness zones, go dormant when days get shorter and colder. During this stage, they should never be fertilized.

Doing so could result in the same over-fertilizing symptoms as using too much, in spring and summer.

However, there are two geographical exceptions to this. 

  1. In warm hardiness zone 11, where frost doesn’t typically occur, you can fertilize your houseplants through winter. But, ONLY at half strength and frequency. 
  2. In tropical climates, where temperatures hover between 77° and 82°F, it’s safe to fertilize houseplants at the same dose and frequency, year-round. 

Verdict: Best Fertilizers for Indoor Plants 

Based on all the great information we’ve covered, the best indoor fertilizer, to keep your houseplants happy and thriving, year-round, is one that matches your application preference and end-result expectations. 

Miracle-Gro Indoor Plant Food (Liquid) 1-1-1 

Best Indoor Plant Food

Miracle-Gro Indoor Plant Food (Liquid) 1-1-1 

Fast-acting, pump fertilizer that couldn’t be easier to use. Gentle and effective on all houseplant varieties, simply pump directly onto the soil.

Liquids such as Miracle-Gro Indoor Plant Food And Neptune’s Harvest Fish & Seaweed Fertilizer provide immediate nourishment, with some options being versatile as both a soil drenche and foliar spray. These are sometimes more economical. But, it needs to be applied more frequently.

Jobe's Indoor Houseplant Fertilizer Spikes 13-4-5 

Best Fertilizer Spikes for Houseplants

Jobe’s Indoor Houseplant Fertilizer Spikes 13-4-5 

Long-lasting, easy-to-apply nutrition for non-flowering houseplants with higher nitrogen for large, vibrant foliage and a strong root system. 

Time-release granules and spikes such as Jobe’s Indoor Fertilizer Spikes are often preferred over those that tend to inundate plants all at once. A slow and steady stream of nutrients gives your plants plenty of time to absorb, process, and benefit from them.

Neptune's Harvest Fish & Seaweed Fertilizer 2-3-1 

Best Organic Indoor Plant Fertilizer

Neptune’s Harvest Fish & Seaweed Fertilizer 2-3-1 

OMRI-certified, organic fish and seaweed liquid concentrate that ensures that foliage stems and roots will experience hardy growth resistance to pests.  

FAQs Fertilizing Houseplants