Fertilizing Houseplants 101

Fertilizing houseplants may seem like a hassle, but for those of us who are houseplant enthusiasts, we know it's integral in maintaining healthy (and happy) houseplants.

Over the last couple weeks, I've had a deluge of "How should I fertilize my houseplants?" questions. So much so, that I also decided to dedicate an entire Plant One On Me episode on fertilizers via my YouTube Channel, which you can view here and will be touching upon it in my new Houseplant 101 Class that I'll be doing with Chelsea Garden Center this May 20th, 2017. 

I assume the influx in questions is because it's the season (the growing season, that is!) that we all should be thinking about giving our growing green friends a little extra boost. Admittedly, I've been lax in the past with my fertilizing schedule, but as my houseplant collection boomed over the past seven years, I had to smarten up and realize that it needs to make it into my houseplant care regime. I know I touched upon fertilizing a bit in my "Beginner's Guide to Houseplants", but this post is meant to make you come away with all the expertise needed to begin a fertilizer routine for your plants. Additionally, I'll share with you the exact products that I use in my home to ensure healthy houseplants. 

Essential elements for plants

Plants require sixteen elements for photosynthesis, growth and metabolism. This includes: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), zinc (Zn), molybdenum (Mo), boron (B), copper (Cu), manganese (Mn), and chlorine (Cl). Carbon, hydrogen and oxygen are essential—but they aren't considered nutrients like the rest of the elements. The macronutrients, which are required in much larger amounts, are N, P, K, Ca, Mg and S. Of these macronutrients, N, P, and K are considered "primary nutrients" and they will be the subject of discussion here. 

Why plants need fertilizers

In order for soil-based plants to look their best, taste their best (if you're eating them), and grow the best, you'll need to fertilize them. This is largely due to the fact that as plants grow, they extract nutrients from the soil. Because these plants are in a closed system (e.g., in a pot in our home), and not exposed to external nutrients as they would in their native environments, (like rotting wood, humus, and animal scat), they need soil that has been amended with fertilizers. This will allow you to replenish any nutrients that have been lost over the growing months. 

The N-P-K ratio

When you are considering purchasing a fertilizer, you'll notice that most fertilizers will have three numbers, like 10-10-10, 10-30-10, or 12-6-6, for example. The first number is always "nitrogen", the second is "phosphorous" and the last number is "potassium", hence the phrase "N-P-K". This ratio represents the available nutrients by weight in that particular fertilizer, so if I have a 1 pound container of fertilizer with an N-P-K ratio of 12-6-6, that means it has .12 pounds of nitrate, .06 pounds of phosphate, and -.06 pounds of potash (potassium). The rest of 0.76 pounds is actually just filler material or bulking agent. You may often here someone at a plant shop talk about a "balanced fertilizer". This simply just means that all numbers of the N-P-K ratio are the same, so a 10-10-10 or 20-20-20, for example  

These nutrients are integral for a number of reasons, and I'll explain their importance here:

Nitrogen is not only a major component of chlorophyll (C55 H72 O5 N4 Mg), which is vital in photosynthesis—allowing plants to absorb energy from light, but it also makes up amino acids that produce proteins, which just like in our bodies, produces new tissues. Plants are exceptionally hungry for nitrogen, and the combination of nitrogen and phosphorous from agriculture fertilizers washing into our oceans, often causes those algal blooms that we often hear about, which choke out the oxygen in our water bodies due to extreme plant growth. Nitrogen is particularly important for leafy plants, like Philodendrons and Dieffenbachia; if you feed a blooming plant too much nitrogen—it might not actually fruit or flower—or may just flower less. 

Phosphorus is really important for roots, buds, fruits and flowers. It transfers energy from one part of the plant—say the root zone—to the buds. It's also vital in cell division and tissue production. For plants that flower, or are equally grown for both foliage and flower, I often use a fertilizer with a higher second number, so say a 20-30-10. 

Potassium is not incorporated into the chemical makeup of a plant, but that doesn't mean it's no less important. On the contrary, it's imperative for vitality and vigor—and it will overall create a higher quality plant. Potassium is super essential for catalyzing enzymes in a plant—at least 60 of them—which again, is important for protein synthesis and ultimately plant growth. Potassium also regulates the opening and closing of the stomata, or plant pores. This is where the CO2, O2 and water vapor is exchanged. Less potassium in the soil means that excessive water loss can occur in the plants—both from the roots as well as from the stomata, which can dry and desiccate plants. 

Applying fertilizer

When I apply fertilizer, it's important to note that I dilute everything by half of the recommended limits. So, if it's suggested that you apply 1/2 teaspoon per gallon of water, I dilute it to 1/4 teaspoon. It's best to be conservative when applying fertilizer...seriously so. Applying too much fertilizer and too frequently can burn your plants and reduce the ability for plant roots to uptake nutrients.

For most of my fertilizer application, I use a CoreGear DEWS GARDEN 1.5 Liter 50-Ounce Multi-Purpose Hand Sprayer, which is designed to not clog when adding water-soluble fertilizer. I'm sure there are a lot of great products in the market, but this one has been more than adequate for me, and I particularly like how the spray can be misted or directional, depending on how you adjust the nozzle. I'll be using this both indoors and outdoors, and it's heavy-duty enough to be tossed around a little bit without any breakage. I go more in-depth as to how to use this in the 12th edition of Plant One On Me—my gardening Q&A on YouTube here

In some cases, I foliar feed my plants—particularly the Tillandsia and Bromeliads. Foliar feeding can have a nutrient efficiency uptake 8-9 folds higher than soil feeding. The uptake all depends on the spray solution, environmental conditions surrounding the plant, leaf characteristics and plant state. These are not things we'll get into today, but I just wanted to let you know that foliar spraying is a viable way to get nutrients to plants. I use an Air Plant Food and Fertilizer and even though it's a tad expensive, I find it to be relatively convenient. 

Because I have well over 540 plants in my home now (the mere sound of that sounds so excessive), I have to have some sane plan of action for fertilizing the plants. I get into this more in Plant One On Me here with a screenshare of my "mad plant scientist" spreadsheet. Basically, I document the genus and species of plant that I have, when I should fertilize it, what fertilizer I should use (I color code it with the brand of fertilizer), and the last day that I fertilized the plant. Additionally, I have what room(s) the species of plant is in, just as a reference, in case I have a minor lapse of memory. But basically, I refer to this master spreadsheet of plant care and organization every Sunday, so I can check frequency and fertilizing plants. Here's an example of the columns that I just described: 


This level of organization allows me to keep on schedule and ensure that I'm giving my plants what they need. In the case of fertilizing the soil, I always make sure that the plant is well-watered. If it is too dry, then the fertilizer won't be able to make it to the roots, and it'll be rendered ineffective. I often then just take my hose and water the plants generously, and then use the CoreGear DEWS GARDEN 1.5 Liter 50-Ounce Multi-Purpose Hand Sprayer with diluted fertilizer mix to "top off" the plant. 

Plant fertilizer requirements

In my spreadsheet I have a far more detailed description of various plant fertilizer requirements, but in lieu of getting too in-depth, here are some suggested levels of the more popular houseplant genera. Please keep in mind that I do not fertilize my cacti or succulents, and from my experience, you really shouldn't have to. 

Members of the  Marantaceae  family generally require a monthly dose of 10-10-5 fertilizer, spring through fall.

Members of the Marantaceae family generally require a monthly dose of 10-10-5 fertilizer, spring through fall.

10-10-5 Fertilizer

  • Calathea sp. (monthly, spring through fall)

  • Maranta sp. (monthly, spring through fall)

  • Stromanthe sp. (monthly, spring through fall)

Peperomia  and other popular houseplant species manage well under a balanced fertilizer.

Peperomia and other popular houseplant species manage well under a balanced fertilizer.

10-10-10 Balanced Fertilizer

  • Anthurium sp. (monthly, spring through fall)

  • Spathihyllum sp. (monthly, spring through summer)

  • Zamioculcas sp. (4 times per year)

  • Pachira sp. (biweekly, spring through fall)

  • Oxalis (monthly)

  • Peperomia (3 times per year)

  • Ficus (monthly, spring through fall)

  • Cissus (every three weeks)

  • Strelitzia (monthly, spring through fall)

20-20-10 Fertilizer

  • Alocasia sp. (every two weeks, spring through fall)

Syngoniums  love a balanced fertilizer like a 20-20-20.

Syngoniums love a balanced fertilizer like a 20-20-20.

20-20-20 Balanced Fertilizer

  • Aglaonema sp. (monthly feedings, spring through summer

  • Dieffenbachia sp. (biweekly, spring through summer; monthly, fall through winter)

  • Philodendron sp. (monthly, spring through fall)

  • Syngonium sp. (biweekly, spring through fall; monthly in winter)

  • Epipremnum sp. (biweekly, spring through fall; monthly in winter)

  • Monstera sp. (biweekly, spring through fall; monthly in winter)

Blooming plants, like  Begonias  and  Cyclamens  appreciate higher phosphorous in their fertilizer.

Blooming plants, like Begonias and Cyclamens appreciate higher phosphorous in their fertilizer.

10-20-10 / 10-30-10 Fertilizer

  • Begonia (feed every three weeks)

  • Cyclamen sp. (feed every two weeks)

Tillandsia,  or air plants, love a foliar spray from time to time.

Tillandsia, or air plants, love a foliar spray from time to time.

17-8-22 Fertilizer

  • Tillandsia (once a month, spring through summer)

Some essential fertilizer gear

A number of folks have asked specifically what gear and fertilizers I use in the home. Here are some links to my products. I also use a "compost tea" and homemade vermicompost as a soil amendment, but this is generally for plants that need a little drop in pH or a little extra nitrogen. Of course, if you like certain products that I don't list here, please contribute below in the comments section so that other folks can consider! But, these are my choices: 

Above: This is the main "spray bottle" that I use to disseminate the fertilizer for my plant. If I use different fertilizers, I make sure to wash out the previous fertilizer so there is no leftover residue. 

Above: This is the foliar spray that I specifically use for my Tillandsia and Bromeliads. That group of plants typically only require fertilizer every month during the growing season.

Above: This is an all purpose balanced fertilizer that I dilute by half and primarily use for my leafy foliage, like Philodendrons and Monsteras. 

Above: This is a fertilizer that I often use for plants that are grown both for flowers and foliage, as it is a 2-3-1 ratio. 

Above: I will use this fertilizer, which has a ratio of 1-3-1, primarily for my flowering plants.

Above: I don't use this fertilizer as much, but in some cases, plants like my Fatsia japonica, prefer this ratio of 12-6-6. 

I hope this post helps in getting you on track with your fertilizing regime! And if you haven't yet, check out the Plant One On Me episode below all on fertilizing. Of course, if you have any more questions, please feel free to write them below or in the Comments section on my YouTube channel. Happy fertilizing! 🌿