Mother Nature has had millions of years to perfect her gardening skills, and to this day, we’re still trying to figure out all of her secrets.
In the process, we’ve done something nature never intended – moving plants from their natural habitats to grow them in places they would never have otherwise survived.
While we’re slowly developing hardier cultivars of popular plants to help offset these changes, we’ve made one huge change that requires a bit of extra effort on our part.
This change, of course, is turning normal plants into houseplants or indoor plants.
Mother Nature never intended for plants to grow inside giant boxes usually made of other dead plants, so it should be no surprise that special care is needed that would be automatic in their natural habitat.
One of these is the ongoing debate about whether houseplants need fertilizer and what types of fertilizer they should have.
Should You Fertilize Houseplants? If So, How?
With VERY few exceptions, the answer to this will always be a resounding yes.
But to understand how to fertilize, we must first look at why houseplant fertilizer is necessary and what it does.
Why Fertilizer is Necessary
Oddly enough, most popular houseplants originated in forests, especially those within tropical or subtropical regions.
This means they often have some basic shelter from the sun, leading to a soil that dries out slower but is less likely to flood.
As the canopy above ages, dead leaves fall to the ground, creating a layer of debris.
Microorganisms and insects then break the debris down into its basic nutrients, which are absorbed into the soil.
The result is a perfectly balanced ecosystem that plants have adapted to, often to the point where a certain species won’t grow outside of its natural habitat without human intervention.
But what happens when you shove one such plant into a pot?
Potting soil contains some degree of nutrition built in, as do soil-free mixes, which often seek to emulate the decomposition process. However, this nutrition simply isn’t enough.
As the indoor plant grows, it consumes the nutrients, spreading its roots in search of additional nutrients.
Picture sitting in a closet with a large bowl of salad. As time passes, you will continue to eat the salad, but what happens when the bowl is empty?
This is the same thing that’s happening to your potted plant.
Fertilizing a houseplant is similar to someone reaching into the closet and refilling your salad bowl. Feeding helps keep your indoor plant strong, promotes healthy growth, and combats nutrient deficiency.
Common signs of nutrient deficiencies in your plants include delayed blooming, stunted growth, and discolored leaves.
But before we get into how you should fertilize, we have to cover a few important aspects of fertilizers that can make all the difference between giving our plant food and poisoning it.
The first thing that needs to be covered is the nutritional value of fertilizer.
The fertilizer packaging contains its own version of a nutrition label, with most macro and micronutrients being listed on the back.
However, the three most important macronutrients are prominently listed on the fertilizer label in the form of a ratio.
These three nutrients are:
- Nitrogen (N) – Essential for healthy foliage growth and green growth in all plants.
- Phosphorus (P) – Used primarily to encourage blooming, although it also aids the plant’s immune system.
- Potassium (K) – Like humans, this nutrient is essential for strong stems, a healthy immune system, and recovery from pruning.
These three main nutrients (NPK for short) can be found in commercial fertilizers, which have a non-burning formula for your houseplants’ foliage and roots.
Many indoor gardeners prefer a balanced NPK ratio, such as 10-10-10. This offers a good balance that keeps you from going overboard with feeding your houseplants that require fewer amounts of fertilizer.
However, it’s also a common practice to use a higher nitrogen formula during much of the year to encourage growth, then switch to a lower nitrogen, higher phosphorus mix during the plant’s bloom time to encourage the best blooms.
Liquid Water Soluble Fertilizer vs. Slow-Release Fertilizers
There are various types of fertilizers you can use on your houseplants. There are liquid fertilizers, slow-release, synthetic fertilizers, and organic fertilizers like peat, manure, worm casting, slurry, seaweed, and guano (bat fertilizer).
But among these, liquid-soluble fertilizers should always be your go-to for houseplants.
These fertilizers are specially formulated to dissolve in water so your plant has access to all nutrients when needed.
You can dilute this type of fertilizer so that younger or more sensitive plants won’t be overfed or risk chemical burns.
Another benefit of liquid fertilizers is that they’re very easy to use and can act as growth enhancers for your indoor plants.
Granular, slow-release fertilizers are quite different, however.
The granules are designed to break down over a period of time, but this process is uneven, resulting in periods where the plant gets too much of one nutrient and too little of another.
Another disadvantage to using granular fertilizers is that they aren’t instantly available, and it is common to run the risk of over-fertilization since most are time-release.
As such, we don’t recommend using slow-release formulas, as they can cause all sorts of problems, like damage to houseplants over time.
Risks of Improper Fertilizer Use
Another important thing that should be brought up is that using fertilizer on houseplants does come with some risks, as you are trying to emulate a natural process.
Deficiencies can make your plant ill but are often easily fixed by using a supplement or tweaking the amount of fertilizer you give it.
Too much fertilizer, however, can cause damage over time, like chemical burns, and leave excess soluble salts behind in the soil, which can eventually poison your plant. You may notice brown leaf tips on your houseplants when there is fertilizer burn.
Repotting or flushing the soil can help keep the number of mineral salts low.
Finally, using the wrong fertilizer can affect plant growth, causing leggy growth, failure to bloom properly, or other developmental issues.
Is There a Single Go-To Method for Fertilizing Houseplants?
Sadly, there’s no single solution for every plant, which is why you’ll find so many different fertilizers out there.
In fact, one species of cultivar may have very different needs than another species or cultivar within the same genus.
This is why balanced fertilizers are so popular, as they can provide a generally safe amount of nutrition for your plants if you don’t know the specific ratio they need.
You should also pay attention to packaging and purchasing fertilizers designated for your plant when possible.
NOTE: In general, do not fertilize indoor plants during the winter months.
Final Notes: How to Fertilize Your Houseplants
And now, it’s time to wrap everything we’ve discussed together and figure out how to apply them.
As mentioned, you should always strive to find your plant’s exact fertilizer needs.
When you don’t know the species or cultivar, you can usually resort to a fertilizer marked for the genus or type of plant (such as Miracle-Gro’s famous rose food).
Always use a liquid-soluble fertilizer and follow the exact instructions on the packaging of the fertilizer container.
If you know your plant, you should follow the frequency and dosage listed in the guide. As a rule of thumb, only fertilize your houseplants when they are actively growing. Also, there’s no need to feed them when they go through a rest period, as they are dormant and not growing and won’t need those extra nutrients.
Try to get an accurate NPK ratio, but you can default to an all-balanced fertilizer if you don’t know the specific needs.
Most importantly, don’t be afraid to experiment a little.
Plants have their own personalities, and you may find your plant needs a little more or less fertilizer than other plants.
You may also find you need to occasionally provide a supplement, such as Epsom salts (phosphorus) per gallon of water or eggshell tea (calcium).
If you live in a tropical climate, provide your houseplants with a summer fertilization schedule year-round.
Let your plant tell you if it needs more or less of a nutrient and adjusts as needed.