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How to Fertilize Houseplants: And the 1 BEST Fertilizer!

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I continually get tons of questions on how to fertilize houseplants over the past months, so I’ve decided to write a comprehensive post on the topic.  Fertilizing can be so confusing for the beginner houseplant lover, but I will make it easy for you, I promise!

You are probably wondering…When do I fertilize? Which fertilizer should I use? How often should I fertilize? Should I fertilize in the winter? What do the numbers on a fertilizer label mean?

The answers to this and MORE is up ahead, so keep reading! And I will present to you my absolute favorite fertilizer that I’m sticking with because it is so amazing and easy to use!

best houseplant fertilizer

After reading this post, you should feel more empowered with basic fertilizer knowledge and know how and when to properly fertilize your houseplants.

Why Should You Fertilize Houseplants

In nature, plants constantly replenish their nutrients from decaying organic matter. 

As leaves, branches, animal life, and other organic matter decompose, they’ll slowly release and recycle their nutrients into the soil and make it available for plant growth.

In your houseplant pots, the soil can be quickly depleted of any nutrients rather quickly and it will be your job to fertilize. 

Most houseplant potting mixes are “soilless” mixes using peat, so they intrinsically have little to no nutrient levels, and many have added fertilizer that will support plant growth for a few months.

Potting mixes like Miracle Gro Potting Mix are fabulous. This is one that I use very often. It already has some fertilizer mixed in and your plant will be good for up to 6 months, but after that, you’ll need to fertilize regularly.

best soil for indoor plants

Fertilizing and soil chemistry is a very complicated topic, but this post will cover very basic knowledge that will be helpful for you and your houseplants.

Basic Fertilizer Information

When you look at a fertilizer label, you will see 3 numbers.  For example, 10-10-10. 

These represent the 3 primary nutrients that plants need to grow.  Soil nutrients are classified based off of the amount that they are needed by plants. 

The following list shows the most important plant nutrients in decreasing order of usage by plants:

Primary nutrients are needed in the largest quantity and these are Nitrogen (N), Phosphorus (P) and Potassium (K). 

The 3 numbers on every fertilizer label is called the NPK ratio where N, P, and K represent the chemical symbols for those elements.

Historically though, the amount of “P” or phosphorus in fertilizers is expressed as phosphate (P2O5). And the amount of “K” or Potassium is expressed as potash (K2O). Just a bit of technical information.

If you don’t understand, that’s ok! Just move on (my background is in chemical engineering so it makes sense to me…but keep reading!)

Confused? Keep reading…

Secondary nutrients are needed in smaller amounts, but are still important.  These include Sulfur (S), Calcium (Ca), and Magnesium (Mg).

Micronutrients are only needed in very small amounts, but they are still very important.  Micronutrients include Zinc (Zn), Iron (Fe), Copper (Cu), Manganese (Mn), Boron (B), Molybdenum (Mo), Chlorine (Cl).

In very simplistic terms, here is an explanation of NPK:

Nitrogen (chemical symbol N) is needed for growth of leaves.

Phosphorus (chemical symbol P) is important for flower and root development.

Potassium (chemical symbol K) helps to bolster disease resistance, cold tolerance and protection against drought.

So when you see a fertilizer label, for example with 10-15-10, this is telling you the NPK ratio.

This tells you that the fertilizer container 10% Nitrogen, 15% Phosphorus (expressed as phosphate), and 10% Potassium (expressed as potash), respectively.

When to Fertilize Your Houseplants

In general, you should only fertilize your houseplants when they are in active growth.

In my climate, most of my houseplants are in active growth from approximately February through September or October.

indoor ferns

During the dismal winter months, with short days and reduced light, I stop fertilizing.  The only exception I make are for moth orchids if they are growing a flower spike.

If you are growing plants under lights year round, they may keep growing year round, so go ahead and fertilize year round! Unless your plant decides that it is taking a break.

When NOT to Fertilize Your Houseplants

Fertilizing is not a fix for poor cultural conditions!  If you have a plant in poor light that is not growing, your focus should not be fertilizer. 

You should first position your plant in a brighter area.  Light is paramount for growth! 

First fix your plant’s lighting conditions, and then when it starts to grow, you can further support the growth by fertilizing.

In the same way, if you have a plant that is not flowering, don’t think that adding a fertilizer high in phosphorus will help you. 

Fertilizer will not cause your plant to bloom.  Ensuring the proper light for your plant WILL! 

The fertilizer will simply increase the size and amount of your flowers.  When you have the combination of appropriate light along with an appropriate fertilizing, then you are winning!

Do not fertilize your houseplant if it is in a period where it is not growing.  Most of my houseplant growth pretty much comes to a halt in the winter months, so I completely cut out fertilizing when light levels are low.

If your plant’s potting mix has gone completely dry, don’t apply fertilizer, especially if it’s at full strength.  You may burn the plant roots. 

A good idea would be to first moisten the soil with plain water first, and then come back and fertilize later.

And whenever you do fertilize, be sure to follow the direction on the label and actually measure out exactly the amount that is needed!

Fertilize with Every Watering

This is my preferred method to fertilize houseplants.  You could fertilize at full strength at whatever frequency the fertilizer label recommends, but I prefer to fertilize with every watering at a diluted strength.  Why?

Number 1 reason…I don’t have to remember when I last fertilized since I’m doing it every time!

There is also a much lower risk of burning your plant, depending on the type of fertilizer that you’re using.

It is also a much more natural way for a plant to receive nutrients.  In nature, plants receive nutrients slowly from decomposing organic matter.

Many fertilizers are designed to be used at every watering.  If you have one of these fertilizers, simply follow the directions!

If you have a fertilizer label that says to dissolve a teaspoon per gallon per month, I would recommend reducing it to one fourth and use that every time you water.  

Or if the fertilizer label says to add a certain amount and use it every 10-14 days, reduce that quantity in half to use for every watering.

Every so often, I would recommend watering your plant with just plain water, even during the growing season. 

This will help flush out any excess fertilizer salts that may be building up in your pot.  Terra cotta pots are notorious for fertilizer salt build up since they are so porous.

Also, you may see some crusty buildup on the surface of your soil, or along the inside perimeter of the pot.  This indicates excess fertilizer salts, or even salts from hard water that built up over time. 

Flushing with clear water every so often, once every month or every few weeks, will help with this issue.

Types of Fertilizer for Plants

I have several recommendations of fertilizers in this section and have used all of them with great results.   All of them are available on Amazon.

All-Purpose Fertilizers

Dyna-Gro Grow

My favorite all-purpose liquid fertilizer by far is Dyna-Gro Grow. I’ve achieved fantastic results with this fertilizer and I use it on all of my tropical houseplants and orchids!

This fertilizer has an NPK ratio of 7-9-5, which is good for both foliage growth and for blooming so you can get away with not switching to a bloom booster fertilizer.

It’s a premium, complete fertilizer that contains all of the 16 minerals that are essential for plant growth. Not all fertilizers are equal, and Dyna-Gro Grow is an exceptional one. You won’t be disappointed.

It is the one-stop shop of houseplant fertilizers. If you only want to use one fertilizer for everything, use Dyna-Gro Grow. You can even use it for hydroponic growing (growing plants with just water) and even as a foliar spray.

It is even urea-free and won’t burn your plants! If you are serious about plants, don’t waste your time with poor quality fertilizers.

Just be sure to follow the directions on the label for the various uses!

Be sure to measure out the amounts exactly! I have dedicated measuring spoons to measure out the amount of fertilizer, and I mix it with water in 1-gallon jugs when I need to water.

Osmocote

Have you ever wondered what those little tiny balls in your potting soil are when you purchase a houseplant?

Those are actually balls of time-release fertilizer, like Osmocote, which slowly releases fertilizer with every watering.

The beauty of Osmocote for houseplants, or even for outdoor plants, is that you can apply the fertilizer, mix it into the soil and not have to worry about fertilizing again for up to 6 months!

This is definitely the easiest method to fertilize, although it is not a complete fertilizer like Dyna-Gro Grow.

There are some specialty fertilizers which you may choose to branch off into once you get comfortable with fertilizing. 

Other Specialized Houseplant Fertilizers

There are some fertilizers on the market for specific types of plants. Here are some of the ones that I have used.

Airplants

For my air plants (Tillandsia) and bromeliads, I use the Grow More 17-8-22 fertilizer which has produced amazing results for me!

tillandsia fertilizer

Succulents and Cacti

For cacti and succulents, I’m currently using a Schultz 2-7-7 formulation.

how to water succulents

African Violets

My African Violets respond very well to the Optimara 14-12-14 fertilizer made specifically for these plants.  They absolutely thrive on this and the growth and flowering has been out of control!

african violet fertilizer

Natural Fertilizers for Houseplants

If you are looking for an organic, natural fertilizer for your houseplants, look no further than fish emulsion.

Be careful what kind of fish emulsion fertilizer that you use though because they can be stinky. Alaska Fish Emulsion Fertilizer is FABULOUS stuff.

Even though it is “deodorized,” I find that it still has a smell so I don’t like to use it indoors. When I bring my houseplants outside though, this is what I use and they just LOVE it.

I use Alaska Fish Emulsion Fertilizer all summer on my houseplants that I bring outdoors. If you do bring your houseplants outdoors, which I highly recommend doing, be sure to harden your plants off.

Final Thoughts on Fertilizing

Fertilizer is NOT a fix for improper light and poor watering habits.

You should ensure that your houseplants have the appropriate lighting for the variety of plant that you have, and that you are using proper watering techniques FIRST. 

Once you have these down, then you can focus on fertilizing your plant in order to achieve the best growth that you can in our artificial indoor conditions!

Fertilizing a plant that is in poor light can cause more harm than good.

If you have a flowering houseplant that is not flowering, the reason is likely not enough light.  Fertilizing your plant will not cause it to bloom.  Moving it to higher light will.  The fertilizer will simply enhance the blooming.

Lastly, I can’t overemphasize how great Dyna-Gro Grow is. As some now to your normal plant care routine and you will be pleased with the results!

Hopefully this post has helped you understand some important aspects of fertilizing your plants.  Comment below with any questions!

Please do me a favor and share this post to social media because it will help me spread the Ohio Tropics houseplant care tips to the masses! Also, check out my shop on Amazon for all your houseplant care needs:

OHIO TROPICS PLANT CARE STOREFRONT

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Kay Slaughter

Thursday 23rd of April 2020

I did buy a small bottle of the dyna grow. Now when I water my plants throughly, do I throughly water them with the dyna grow that I mixed in a gallon of water?. As you can tell by my question, I'm a newbie.

Raffaele

Thursday 23rd of April 2020

Hi Kay! Yes, just follow the directions right on the label. Mix 1/4 to 1/2 teaspoon per gallon of water and use it every time you water!

Michele Jones

Tuesday 3rd of March 2020

Thank you for all your posts! I didn't read all comments so I don't know if you answered this! Can you use Dyna-grow on Hoyas? Thanks again! Michele

Raffaele

Tuesday 3rd of March 2020

Hi Michelle, you're very welcome! Yes you can use it on Hoyas, absolutely! I use it for mine :-)

Terri

Monday 6th of January 2020

I just started collecting houseplants about 31/2 years ago and have never fertilized them once because I've been afraid of doing it wrong. So this article is very helpful., just last week when I was reading your article on watering I thought to myself " I so hope there will be something on fertilizing before spring comes " I have bought several kinds of fertilizer so I'm hoping what I have will be useful but wanted to ask your opinion first. I would prefer to use the worm castings and also a product I purchased here in Canada called Marphyl marine plankton ( micro seaweed ) Would these be suitable and can I use them both or just one or the other ? And would they be sufficient or should I add something else ?

Lana

Thursday 19th of December 2019

You fertilize your Tillandsia? How? Actually how often do you soak them and when you do, do you add fertilizer to their water? Better do an article just on air plants. On my area an air plant is a throw away plant. Sad right? Same with bromeliads and kalanchos. Supposedly our air is way to dry for them.

Raffaele

Thursday 19th of December 2019

Hi Lana. Yes, I do actually have a blog post on air plants and you have to water them and occasional fertilizing is very beneficial. Here is the blog post: https://www.ohiotropics.com/2019/05/07/complete-guide-to-growing-airplants/

Kat

Wednesday 12th of June 2019

Hello! Could you say a bit more about moistening the soil before fertilizing it? I am wondering how much water to put for this first "moistening" step. I typically water until water runs out of the drainage hole. If I am going to be fertilizing after, should I be watering less in the "moistening" step? If I water too much during the first step, will the fertilizer just run right out without absorbing at all? Thanks!

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Wednesday 12th of June 2019

You are watering the right way. The moistening step is really only needed if the soil is bone dry and you are using full strength fertilizer. If you water dilutely at every watering and/or the soil is not super dry, you don't really have to bother pre-moistening. Hope this helps! This will minimize fertilizer burn.

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