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Beginner guide to fertilizing houseplants – why? when? & how?

You may be wondering if it’s necessary to fertilize a certain houseplant or what type of fertilizer should you use. You may even be wondering what is a houseplant fertilizer in the first place, and that’s also a great question. To understand more about houseplant fertilizers, when to use them and how, keep reading this article.

In this article you’ll find:

  • What is a houseplant fertilizer and is it really necessary to fertilize our houseplants
  • When do we need to fertilize our houseplants
  • How to fertilize houseplants

What is a houseplant fertilizer and is it really necessary to fertilize our houseplants?

You probably heard about the process called photosynthesis. In this process plants, using light, water (H2O) and carbon dioxide (CO2) create their own food (C6H12O6) while releasing oxygen (O2) into our space. So, the main source of food for the plant are the carbohydrates the plant created itself.

What is fertilizer then, if not plant food?

Fertilizer is like a plant “supplement” rich in nutrients, such as potassium and iron. In nature it’s self created by the decomposition of other organic sources, but to plants indoors, who live in a closed and controlled environment, we are the ones who need to provide them with those additional nutrients.

In the long term, these additional nutrients help our plants with better root growth and a better immune system overall.

Which nutrients houseplants need?

Plants need a wide variety of nutrients. Accordingly, we differentiate macronutrients and micronutrients. The difference is only in the amount of nutrients that plants need.

There are the main three macronutrients that plants need in a higher amount, and those are nitrogen (N), phosphorus (P) and potassium (K). These three make the most % in a fertilizer and are usually pointed out on the packaging as N-P-K. Some other macronutrients are also calcium and magnesium.

Then we have micronutrients that are also important, but plants need them in less amounts. Some of those are iron, zinc and copper.

More fertilizer does not equal a healthier and happier plant.

It’s important to understand that water soluble fertilizers, such as those liquid ones you can find in every store nowadays, come in form of salt. That’s why it’s important to not over fertilize our houseplants, because an excessive amount of salts can built up in the pot/soil and can burn and damage the plants roots, seriously damaging the whole plant.

What N-P-K means?

N-P-K + some numbers, such as 10-10-10 or 5-5-5, is what you’ll see on most fertilizer packaging. The numbers represent the amount (percentage) of primary macronutrients – nitrogen (N), potassium (K) and phosphorus (P) in that specific fertilizer.

Nitrogen (N) is important for the absorbance of light and creating new leaves (affects formation of chlorophyll). Phosphorus (P) is important for root, flower and fruit growth. Potassium (K) it’s important for water regulation (stomata and water flow) and food storage.

Usually a well balanced fertilizer, that has equal amounts of “the big three” are great for almost all houseplants. And that’s actually what I use for the majority of them.

If you have plants that are flowering, you’ll want to use a fertilizer that has higher phosphorus percentage because it helps with flowering. Here you can find specifically Orchid fertilizers, for example.

Other types of plants that require different amounts of nutrients are, for example, citrus fruits (like lemons) and succulents (including cacti).

It’s always good to read about a certain plant and find out what fertilizing needs it requires.

If you are searching for a universal houseplant fertilizer, make sure it’s labeled for houseplants and that it contains both macro and micronutrients.

Types of fertilizer

There are organic and inorganic fertilizers, and both come in liquid or some other water soluble form.

Organic ones are made from natural ingredients while inorganic fertilizers are artificially manufactured. Some of the most common organic fertilizers are fish emulsion, warm castings, bone meal etc.

Its really up to you what type of fertilizer you’ll use. The only important thing is that you fertilize your houseplants in one way or another.

I find it great to mix warm castings into the soil mixture right at the beginning when repotting/planting the plant, and then, after a month or two, begin fertilizing with fertilizer in liquid form.

I do prefer liquid over slow release fertilizer because I have the feeling I’m the one in control of how much fertilizer I give to my plants and they are not getting fertilizer with every watering (like when you stick those fertilizer sticks into soil). But it’s entirely up to you which type of fertilizer you’ll use.

When do we need to fertilize our houseplants?

Now that we covered what a fertilizer is and why it’s important to fertilize our houseplants, let’s move onto the practical part – WHEN & HOW to fertilize our houseplants.

Growing season & dormancy period

Houseplants don’t need to be fertilized all year round. They have their growing and dormancy periods throughout the year. Even if they may be growing indoors during winter, it’s far less growth than during their actual growing period.

You need to fertilize your plants only when they are actively growing, in other words, during the growing season.

The growing season starts somewhere in early spring and it lasts up until fall, when temperatures begin to drop and days become shorter.

The growing period will also be affected by the part of the world you live, of course. If you live in Canada for example, the growing season for your plants will be far shorter than for those plants that are growing in Florida.

Personally, I like to back off from the fertilizer from December to February/March, even if I see some new growth on my plants.

If you want to fertilize them even during winter (they must be growing, if they’re not don’t even think about fertilizing them during winter), use a more diluted mixture.

Use a more diluted mixture also at the very beginning of your “fertilizing period”, for the first couple of times and then proceed to the advised amount of fertilizer (never more than that).

The second important “WHEN” to fertilize

Fertilize your houseplants when they are healthy and thriving.

If your plant is not feeling good, giving it additional fertilizer (salts) may produce even more stress to an already stressed houseplant.

It’s rarely the case that the plant looks bad because of lack of nutrients. That’s usually the last thing causing problems to your plant. Main reasons for a sad looking plant are usually pests, or it may be a watering problem (usually overwatering) or lack of light (their leaf color fades when they are not receiving enough light).

How to fertilize houseplants?

When using fertilizers it’s always important to read the instructions on the packaging. Never use more fertilizer than indicated. Let’s see this on an example.

You bought a fertilizer in liquid form. This types of fertilizer usually have measures like one bottle cap per half gallon of water or 3 caps per gallon of water.

This is always different and will vary from brand to brand. That’s why you need to read the instructions, there’s not a general guideline.

When you learned what amount of fertilizer goes on a certain amount of water, mix those two together, shake the bottle (I usually use a water bottle for this and not a watering can as I find it’s easier to mix) and you are ready to fertilize your plants.

You do it like you would with watering. Take the bottle or can, and water the soil all around your plant and wait for it to come down the drainage holes.

The excess that drains out, I usually toss right after I finished fertilizing the other plants that need to be fertilized or after 5-10 minutes. I don’t like that salty water staying on the bottom of the pot because of potential mineral build up around the roots. It’s as easy as that.

Don’t stress too much about fertilizing.

The most important thing is that you do it, with any type of universal houseplant fertilizer, at least. And be mindful not to use more than advised! That’s the key to fertilizing.

Remember, more fertilizer does not equal a happier plant.