I’m betting that you have a little green in your home right now. No, I’m not talking about seedlings. I’m talking about houseplants. Nearly all of us have at least a few these days. Houseplants have been a hugely popular trend the past few years, with some plant-a-holics spending big money on a single showstopper.
Unfortunately, those plants don’t always fare so well after we bring them home. It’s not for lack of effort from the “plant parent.” It’s usually the result of following bad advice – care tips which are actually houseplant myths. So, what’s the real story and the science behind what your plants really need? Houseplant myth expert, Robert Pavlis, joined me this week to break down the facts.
Robert isn’t just a plant-lover with years of experience under his belt. He has legitimate science chops. With a background in chemistry and biochemistry, Robert takes on houseplant and garden myths and debunks them on his website, through videos and in his books.
He’s also an avid gardener. His private, 6-acre botanical garden is packed with over 3,000 different species of plants, trees and shrubs. Stay tuned for more garden-related podcasts with Robert, but for now, we’re staying indoors to do a little house-plant myth-busting.
It’s important to keep houseplants watered on a regular basis.
Robert says this is one of the biggest and most common mistakes that well-intentioned houseplant owners make. Unfortunately, the popularity of houseplants has created a boom in bad resources.
There are all kinds of resources out there that tell you how often to water this, that or the other variety. Rarely do you see the same guidelines twice, and that’s because there is no magic bullet when it comes to watering frequency.
How often you need to water depends on all sorts of variables.:
- Type of plant
- Age of the plant
- Type of container (what is it made of)
- Size of container
- Soil type
- Growth rate
That’s a long list, and it still only tells part of the story. All of these factors (and more) affect how your plant absorbs water. Your home environment and many other factors are unique to you. Plus, your plants are living things, which means what works one year may not work the next. So, you just can’t plan on watering on a regular schedule. If you do, you will usually be causing more harm than good for your plants.
Watering is a topic that confuses most beginning houseplant owners. They may hear or read advice to avoid watering “too much.” That doesn’t refer to the amount of water. It actually refers to the frequency of providing moisture. Don’t water “too often” would be a more accurate tip.
Plants often like an intense drenching of water. What they don’t like is a little bit of water every few days. Plants need soil that has a chance to dry somewhat between watering.
Fortunately, watering doesn’t need to be complicated. You may not be able to schedule a reminder on your smartphone, but all you need to know when it’s time to water is your index finger. Robert says the most reliable watering gage is to stick your finger into the soil of the container. If the soil is moist, leave things alone. If it’s dry, Baby needs a drink.
Another tip is to lift the pot. The drier the soil, the lighter it will feel. Initially, the weight of the container won’t clue you in to how moist or dry the soil is, but within several weeks, you’ll start to recognize the difference. That way, you won’t even need to get your finger dirty.
Another thing to bear in mind is the type of plant you’re caring for. There are three categories when it comes to the amount of moisture plants prefer indoors.
- Prefer never to be completely dry (examples are umbrella palm, pitcher plant, most fern varieties)
- Prefer soil that dries a little but not completely (most plants fall into this category)
- Prefer soil that dries completely (cactus, succulent, orchid)
With just a little bit of research, you’ll be able to learn which of those three categories your plants fall under, and you can water accordingly.
This is one time that it’s a good idea not to trust the plant tag. It’s common for houseplants to be mismarked or to include inaccurate care instructions. So, take a few minutes to double-check on your own.
There are some watering devices on the market, but Robert recommends against them all. A common option is a moisture meter connected to some type of auto-watering device. Moisture meters don’t actually measure the moisture level of soil. Instead, they measure the conductivity of moisture through the soil. So, results will vary based on the type and porosity of the soil in your container. Potting soil changes over time too – due to fertilizer, hard water deposits and other factors. That means meter results will change as well.
This really is one of those areas where, to be successful, we really just need to pay attention. More plants die from overwatering than from under-watering. That’s why the finger test is the method I recommend in the garden too. It’s the best way to gauge when your plants need water. I often say that we can love our plants to death. Don’t make that mistake indoors or out. When in doubt, it’s better to underwater.
Well-draining soil can help to overcome our tendency to overdo it with watering. That leads us to our next – and possibly most controversial – myth.
Containers should have stones, pebbles, etc. at the bottom to improve drainage.
It seems logical that a layer of course material under potting soil would encourage excess water to drain away. The science says otherwise.
There haven’t just been a few obscure studies on this. Multiple studies have found that water does not move easily between layers of different particle sizes. Water moves through soil and stops once it hits the layer of course material. It’s not until the soil reaches a super-saturation point that the pressure in the over-saturated soil pushes water to move into the lower coarse layer. Even then, the soil itself remains overly wet.
It’s difficult to do a demonstration of this. I shared a video on my joegardenerTV YouTube channel to show the principle on a small, exaggerated scale in clear, plastic cups. Who would have thought a gardening video would be so controversial? I regularly hear from viewers who call foul (to put it mildly). For the record, I don’t have a personal vendetta against pebbles. I shared the video in hopes that this solid principle of science will resonate with gardeners who are looking to make smart choices.
Robert has written about this in his Garden Myths Book 1 publication too. We both hope that you will trust the science and resist the urge to put any material in the bottom of a container.
So, how can you improve drainage? Stones, sand, pebbles, perlite, and other coarse materials will all achieve that goal, but the trick is to mix the material in with the soil. As long as materials are mixed together, water can continue to move through it. Just avoid creating layers.
If your goal is to lighten a large container – or to use less soil, don’t make the common mistake of filling the bottom with something like a layer of styrofoam peanuts. That layer of different material will also hinder drainage at the point where it meets the soil. Robert recommends turning a smaller pot upside down and placing that in the large container to take up space.
Air humidity around a plant can be raised by placing the container on a tray of water or pebbles and water.
Your grandmother may have even told you this myth. It has been around a long time, but it has no impact on the humidity available to your plant. As water molecules in the tray evaporate, they don’t just head for your plant. They spread out in all directions throughout the room.
Have you ever noticed when someone walks into a room wearing cologne? Depending on how much he or she is wearing, you can smell the fragrance even from a few feet away. The scent molecules are spreading out in all directions – not just up. Water molecules move through the air in a similar way.
When humidity is measured at around a half an inch above the water tray, the air there is more moist. However, measure the humidity level another half-inch higher, and the water molecules have already dispersed. The humidity just an inch above the tray is the same as the rest of the room.
If you mist your plants, the same effect is taking place. Plants don’t absorb the water droplets hanging from their foliage. They experience a few minutes of increased humidity levels before those droplets evaporate and spread throughout the room – just like the water in the tray.
One effective method for increasing air humidity is to reduce the overall size of air space. A good example of that is the recommendation to place plants into a shower stall or the bathtub (with the curtain drawn) to keep them moist when you’ll be away from home for a week or two. This essentially creates a small “room” – with less air space available to absorb the water molecules.
This is the reason humidity in a greenhouse tends to be higher. It’s a smaller, confined space than your home; so there is less air to contain the available water molecules. That small space is also containing more plants per square foot, and since each plant is transpiring (releasing moisture as well as taking in moisture), their combined transpiration raises humidity as well.
If you are genuinely concerned about the humidity level for plants in your home, your best bet is to use a home humidifier. It has the power to increase the level throughout the available air space.
Orchids are difficult to grow
Did you know that there are more species of orchid than any other plant group on the planet? It’s true that some of those can be tricky, but most orchids are tougher than we give them credit for.
Orchids tend to intimidate plant lovers. As a result, we pamper them, when what they really need is to be ignored. In fact, Robert says that most orchid varieties are difficult to kill and do better with neglect.
Overwatering is one of the most common causes of orchid failure. So, Robert tried an experiment with a phalaenopsis orchid (the most common household variety). He removed the orchid from the planting medium (soil), set the plant on the corner of his desk without any source of water, and left it alone. After six weeks of abandonment, the leaves of the orchid had become a little wrinkled from water stress, but otherwise, the plant was just fine.
Orchids don’t need high humidity either. They do just fine in the dry air of our homes, especially the phalaenopsis varieties.
Robert put together a video to demonstrate how he waters his orchids – and what he recommends. He sets the orchid container into a larger pot and fills the large pot with water. Twenty minutes or so later, he removes the orchid container and lets it dry completely before he waters again the same way – usually a week or two later.
The orchid can tolerate sitting in water for a few hours and still be just fine, but don’t keep it submerged for longer.
Maybe you struggle to get your orchid to bloom? Robert has a few tips for that. He recommends providing as much light as possible throughout the summer. If you have an area with dappled sunlight outdoors, that’s ideal – although you will need to acclimate the orchid gradually.
By the end of summer, the leaves should be a lighter, yellowish hue. That’s a good sign – it’s an indicator the plant has absorbed a lot of light. Keep the plant outside as temperatures cool down, but don’t allow it to be kissed by frost. Once temperatures dip below freezing, bring the orchid back indoors for the winter, and it should bloom by Christmas.
Phalaenopsis should flower once a year using this method. Other types of orchids require more light to bloom, so they can be a little trickier. In any case, the principle remains the same. Provide as much light as possible (go easy on direct sun), less water and cooler temperatures.
Robert has good luck with an unheated sunroom, where his orchids receive only about two hours of direct sun and lots of indirect light.
Orchids need orchid fertilizer.
Although the label might say the product is “orchid fertilizer,” Robert says there is no such thing. Check the ingredients. They will be the same as other fertilizers intended for houseplants. The type of fertilizer you use on your other plants is just fine for your orchids too.
Whatever you use, don’t use much. Here again, orchids thrive on neglect. Whatever dosage is recommended on the packaging, use only about a quarter of that strength. Provide that feeding once a month, and your orchids will have all the nutrients they need to be happy.
While we’re on the subject, let’s address the myth that gardeners believe yellow foliage is a telltale sign that the plant needs fertilizer – specifically, nitrogen. There are many potential causes for yellow foliage, so don’t make the mistake of rushing to judgment. Nutrient deficiency simply can’t be properly identified based on the color of foliage.
It’s easy to do more harm than good when it comes to fertilizer.
Orchids will only survive in a greenhouse.
Hopefully by now, it’s clear that orchids are not the dainty prima donnas of the houseplant world as their reputation implies. The truth is they are relatively bulletproof.
Robert says that there are a number of outdated resources which state that orchid growing requires a greenhouse, but for the species available to the average plant owner, a greenhouse is just not necessary.
As mentioned earlier, phalaenopsis are very well-suited to our home environment. Paphiopedilums are another common variety which prefer lower light and can do very well in a sunny window indoors.
At one point, Robert had over 1,000 orchids in his home, and some were specialty varieties. They were happy and healthy. So, don’t be afraid to experiment. Provide as much light as you can (you might even consider adding a grow light), and just don’t overdo it with the water or fertilizer.
Houseplants are great air purifiers
Awhile back, NASA decided to do a study on houseplants. Scientists there decided to find out if the plants were able to remove pollutants from our air. Well, the study determined one thing, but the media spun it in an entirely different direction.
The study’s findings were widely misinterpreted. It was reported by many sources that houseplants clean the air in our homes. Eureka! So, which plant varieties are the best air purifiers? Search the internet, and you will find Top 5 lists and Top 10 lists. However, those lists rarely include the same varieties – and that’s because the reports and the lists are a myth.
Robert got his hands on the original study results. According to the original report, NASA never tested houseplants in a home environment. Instead, they placed a containerized plant into a small chamber (not much larger than the plant) and injected a chemical into the space. Measurements indicated that the potted plant absorbed the chemical from the air.
Are you ready for this? Scientists then cut the plant off and set the pot of soil into the chamber to repeat the test. The pot of soil worked nearly as well as the potted plant. Why? It turns out that the bacteria in the soil was doing the bulk of the work to absorb the chemical in the chamber. The plant’s contribution was minimal.
If you love soil – and are fascinated by the soil food web – like me, that fact may have, simultaneously, blown your mind and not surprised you at all.
The fact is, the study didn’t find any evidence that houseplants have any impact in a home environment. Plants aren’t very efficient at purifying our air at all.
There is an abundance of materials in our modern-day homes which emit a constant flow of chemicals – VOCs. The flooring, paint, furniture, appliances, etc. are putting out toxins at a much faster rate than plants – or their soil – are able to absorb.
So, love your houseplants for all kinds of reasons, but know that – even if you collect masses of plants – they are having a minuscule effect on your air quality.
Potting soil shouldn’t be reused.
Whether you’re growing outdoors in containers or promoting your houseplant to a larger pot, don’t throw out the used potting soil. It is just as viable after a plant has lived in it as when it is fresh out of the bag.
Most potting soils are peat-based mixes. The peat will decompose very slowly, which can cause the volume of soil to shrink. That doesn’t mean it can’t be reused.
If you have hard water, salt (or calcium) can build up and leave a white crust on the surface. The hard water deposits remain mostly on the top inch or so. Remove that, and the rest of the potting soil is ready to use again.
In the garden, we constantly amend in order to build up soil health and nutrient level, but soil in our containers is a very different story. Nutrient level isn’t a concern, because we provide our houseplants and containers with fertilizer on a regular basis. The purpose of soil in a container is to anchor the roots of the plant and to hold water – while being porous enough that excess water will drain properly.
Robert reuses potting soil year after year, and so can you.
Orchids are the exception. They aren’t typically grown in soil, because they prefer a lot of air. In nature, orchids grow on the trunks of tall trees, and their roots grow along the surface of the tree bark. That’s why orchid growing medium is usually small pieces of bark – although coir (coconut husk) is becoming more popular as a less-expensive alternative. Coir is Robert’s orchid-growing medium of choice.
Over time, the bark and coir decompose. As they do, they become finer particles which fall to the bottom of the container, and that can create health problems for your orchid. Robert recommends that orchids be repotted with fresh medium every two years. The spent medium can still be put to use by mixing it with potting soil for your other houseplants.
Information available online is unreliable.
We are able to enjoy many benefits as a result of living in the Information Age, but there are definitely some drawbacks. The internet provides a platform for just about anyone to share information. Unfortunately, the information shared is often unreliable or not based on any truth at all.
The reason many of these and other garden myths exist is because they are spread in videos, blogs, social media posts, etc. These channels provide a forum without a filter, so there is far more misinformation out there than fact.
This is one of my greatest frustrations as a horticulturist, communicator, industry expert, and teacher-at-heart. I cringe every time I see a popular video sharing false garden advice, and it aggravates Robert as well. For every accurate piece of advice, there are at least a hundred inaccuracies floating around, so take anything you watch or read with a grain of salt.
Consider your source, and be a critical thinker. Recognized industry experts or educational websites with the extension .edu are reliable options. Don’t be afraid to experiment, but become familiar with the science – the “why” – behind techniques that work.
Be sure to check out my conversation with Robert by scrolling to the top of the page and clicking the Play icon in the green bar under the page title. Rest assured, you’ll be hearing from Robert again soon in future podcasts. His science-based information is right on point with what I strive to bring you every week.
What variety of houseplant has been bringing you the most joy lately? The options are endless, and it’s always fun to hear what others are growing. I hope you’ll share in the Comments section below.
Links & Resources
joegardener Online Academy: Master Pests, Diseases, and Weeds – Just $47 for lifetime access! Watch for my new course Master Seed Starting coming January 30, 2020!
Garden Myths: Book 1, by Robert Pavlis