7 Houseplant Myths Taken Out of Context: Part 2

Welcome to Part 2 of my Houseplant Myths Taken Out of Context series!

The aim of this series isn't to tell you that every myth is simply wrong. In fact, many houseplant myths started with a little bit of truth or genuine science behind them. The problem is that somewhere along the way, the context gets lost.

So we're going to look at where these popular bits of plant advice came from, what they actually mean, and most importantly, how we can apply that information effectively to the houseplants growing in our homes.

Because sometimes the myth isn't the problem. It's how we use it. 🌱

🌱 Myth #1: Should I microwave my soil to kill fungus gnats?

You've probably heard that microwaving potting mix will kill fungus-gnat larvae and "sterilise" your soil. And yes, heat can be used to pasteurise growing media, but do we actually want our houseplant soil to be sterile?

A healthy organic substrate naturally contains fungi, bacteria and other microorganisms, many of which are harmless or beneficial. Heating doesn't conveniently know which ones we'd like to keep. If you're adding things like mycorrhizal fungi, sterilising the substrate first rather defeats the point.

Fungus-gnat larvae mainly feed on fungi and decomposing organic matter, although they can damage tender young roots and seedlings. They particularly thrive in consistently damp, organic potting mixes.

So instead of automatically microwaving every bag of soil, I'd focus on why fungus gnats are thriving. Start with a good-quality substrate suited to your plant, don't keep it unnecessarily wet and practise good hygiene when repotting. If fungus gnats do become a problem, biological controls such as Steinernema feltiae nematodes can specifically target the larvae.

I personally prefer creating a healthy root environment rather than a sterile one. Researching how your plant naturally grows can help you think about substrate structure, moisture, airflow and biology as one little ecosystem rather than individual problems to eliminate.

And because repotting somehow distributes soil across approximately 97% of my house, I use my Jungle Floor Creative Potting Mat to contain the chaos. It's reusable, water-resistant and designed for repotting, propagation and mixing substrates.

🌿 Takeaway: Healthy doesn't necessarily mean sterile.

🌊 Myth #2: Seaweed is a complete fertiliser

I wrote a blog a while ago about the benefits of seaweed, and since then I've added an update after doing further research. That's part of this series too: sometimes we learn more and need to put our own advice back into context!

Seaweed is packed with interesting compounds and trace nutrients and can be fantastic for soil conditioning, root development and helping plants cope with stress. However, while seaweed can contain nitrogen, phosphorus and potassium (NPK), most seaweed extracts don't provide these macronutrients in sufficient quantities to meet all of a plant's nutritional needs.

This is where the distinction between a fertiliser and a biostimulant becomes important. Seaweed's real strength is as a biostimulant, supporting plant health and growth alongside appropriate nutrition rather than providing everything the plant needs itself.

So I haven't stopped using seaweed. Far from it! I just use it alongside a complete fertiliser rather than instead of one.

🌿 Takeaway: Seaweed is a brilliant addition to your plant-care routine, but don't expect it to provide the whole meal.

🌿 Myth #3: The higher the NPK, the better the fertiliser

First, what actually is NPK?

NPK stands for nitrogen (N), phosphorus (P) and potassium (K), three essential nutrients plants need for healthy growth. You'll commonly see these nutrients declared on fertiliser labels, but here's the important bit: those numbers aren't a quality score.

Take Growth Technology Formulex, for example. It has an NPK of 2.0-0.9-3.3. Put that next to a fertiliser displaying much larger numbers and you might assume Formulex is weaker or somehow worse.

It isn't that simple.

The numbers tell you about the concentration and balance of nutrients in the product. Dilution, how often you feed and how much actually reaches the roots all matter.

And don't stop at NPK. Plants also need secondary nutrients such as calcium, magnesium and sulphur, plus much smaller quantities of micronutrients including iron, manganese, zinc, copper, boron and molybdenum.

So when choosing a fertiliser, turn the bottle around. Look at the nutrient analysis, what else is included, how it's intended to be diluted and whether it's suitable for how you're growing your plants.

🌿 Takeaway: NPK isn't a score. Bigger numbers don't automatically mean a better fertiliser.

💧 Myth #4: Fertiliser salts are bad for houseplants

The word "salt" sounds alarming, but in plant nutrition it doesn't simply mean table salt. Many of the nutrients our plants need are supplied as soluble mineral salts. Once dissolved in water, they form ions that the roots can absorb.

So salts themselves aren't necessarily the problem. Too much salt accumulating around the roots is.

And fertiliser isn't the only thing to consider. Your tap water matters too. If you live in a hard-water area, your water contains higher concentrations of dissolved minerals, particularly calcium and magnesium. Over time, repeated watering alongside regular feeding can contribute to mineral build-up in the substrate.

At excessive concentrations, soluble salts can make it harder for roots to take up water and can eventually damage them. Brown or crispy leaf tips can sometimes be one of the signs.

You might also notice white mineral deposits on your leaves, particularly if you mist or splash them with hard tap water. I like to gently clean my leaves periodically with a soft reusable plant cloth and water to remove dust and residue and keep the leaf surface clean.

There's no need to scrub or use leaf-shine products. Gentle cleaning is enough, and I prefer doing it away from strong direct light and allowing the leaves to dry naturally.

This doesn't mean you need to abandon tap water or mineral fertilisers. Think about the whole picture: your water quality, how much fertiliser you're using, how often you're feeding, your substrate and the needs of the particular plant you're growing.

🌿 Takeaway: Salt isn't automatically the enemy. Excessive salt build-up is.

🌪️ Myth #5: Shaking your houseplants makes them stronger

This one always makes me laugh. We've all seen the reels: someone recreating a miniature rainforest storm in their living room, shaking their plants because apparently that's what happens in nature. 😂 I've particularly seen this advice given for Ficus, such as fiddle-leaf figs.

But, surprisingly, there's some actual science hiding underneath it.

Plants can respond to repeated physical movement from things like wind, rain and touch through a process called thigmomorphogenesis. Mechanical stimulation can change how some plants grow, sometimes producing shorter, thicker or sturdier growth.

But that doesn't automatically translate into "shake your Ficus every morning."

A plant growing outdoors experiences complex environmental conditions over its lifetime. Giving your houseplant a daily wobble isn't the equivalent of recreating its natural habitat, and different plant species respond differently to mechanical stress.

Normal airflow and movement aren't bad things, but if you want stronger, healthier houseplants, concentrate first on appropriate light, nutrition, healthy roots and the growing conditions that particular plant needs.

So by all means recreate a tropical storm in your living room for the Reel. Just don't expect your Ficus to come out of it looking like it's been to the gym. 😂🌳

🌿 Takeaway: Plants really can respond to movement. That doesn't mean shaking them is a necessary part of houseplant care.

🍃 Myth #6: Wind makes your Monstera fenestrate

Following on from shaking our poor houseplants around the living room, here's another one I've seen: give your Monstera more wind and it'll produce more fenestrations.

Fenestrations are the splits and holes that develop in the leaves of plants such as Monstera deliciosa as they mature. There are several theories about why these evolved, including helping large leaves cope with wind and heavy tropical rain, as well as allowing light to reach leaves lower down the plant.

And this is probably where things get a little muddled, because wind really can affect the leaves of some plants.

Large-leaved plants such as banana plants and some Bird of Paradise species can develop splits and tears along their leaves when exposed to wind. Those splits can reduce the amount of wind the large leaf catches and therefore the mechanical force acting upon it.

But that's not the same thing as Monstera fenestration.

Those banana-style splits happen to an existing leaf through mechanical forces. A Monstera's characteristic holes and splits are part of the leaf's development before it unfurls. Pointing a fan at an existing Monstera leaf isn't going to make new fenestrations appear.

It's also worth remembering where Monstera actually grows. Much of its growth takes place beneath and amongst the rainforest canopy, where surrounding vegetation provides some protection from direct wind. As it climbs towards brighter light, its leaves become larger and increasingly fenestrated, so reducing fenestration to simply a response to wind misses a much bigger environmental picture.

For us houseplant growers, it's much more useful to concentrate on maturity, sufficient light, healthy growth and giving climbing species something suitable to climb.

Air movement can still be beneficial in an indoor growing environment, but it isn't a shortcut to giant Swiss-cheese leaves.

A rainforest isn't just wind. It's light, moisture, temperature, airflow, nutrition, competition and the plant's natural growth habit all interacting together.

🌿 Takeaway: Wind can physically split the leaves of some plants, but Monstera fenestrations are a different process. Your fan isn't a hole punch. 😂🌿

🧪 Myth #7: There is one “best” fertiliser for houseplants

“What's the best fertiliser for houseplants?” is a question I see all the time, but I don't think there's one simple answer.

When comparing fertilisers, you'll often see NPK mentioned. This simply stands for nitrogen (N), phosphorus (P) and potassium (K), three of the essential nutrients plants need. As we discovered in Myth #3, though, those numbers aren't a score, and higher doesn't automatically mean better.

So what should we actually be looking for?

Start by turning the bottle around. Look at the nutrient profile, not just the big numbers on the front. Alongside NPK, plants also require nutrients such as calcium, magnesium and sulphur, plus much smaller quantities of micronutrients including iron, manganese, zinc, copper, boron and molybdenum.

Then think about how you're actually growing your plant. A fertiliser that works brilliantly for someone's plants in an organic potting mix isn't automatically the best choice for your plant in semi-hydro. Your water quality, dilution, feeding frequency and growing medium all change the picture.

Some products also contain extras such as seaweed, humic or fulvic acids and other biostimulants. These can be useful additions, but they shouldn't distract us from checking whether the plant is actually receiving the essential nutrients it needs.

And finally, think about the plant itself. I like to research how and where a plant naturally grows rather than trying to force every houseplant into exactly the same routine. Understanding its roots, growing environment, moisture and light requirements can tell you far more than simply asking which bottle everyone else is using.

🌿 Takeaway: There isn't one magic fertiliser for every houseplant. Learn what's actually in the bottle, then choose something appropriate for your plant and the way you're growing it.

🌿 So, are houseplant myths really myths?

A lot of houseplant myths aren't complete nonsense. Somewhere underneath them there's often a little science, an observation from nature or a genuinely useful piece of advice that's simply lost its context.

But context matters even more when we're growing houseplants. We're taking plants that evolved to grow in particular environments and asking them to adapt to life inside our homes. And no two homes are exactly the same. Our light, temperature, humidity, water, airflow, substrates and even the way we care for our plants can all be different.

That's why something that works brilliantly for one person's plant might not work in exactly the same way for yours.

The more I've learnt about plants, the less interested I've become in finding one perfect rule for growing them. I'd much rather understand how and where a plant naturally grows, look at the science behind the advice I'm being given, and then work out how I can apply that knowledge to my growing environment.

After all, we're already asking these plants to grow somewhere pretty different from the environment they evolved for. The least we can do is try to meet them somewhere in the middle. 🌿

Because sometimes the myth isn't the problem. It's how we use it.