21 Common Indoor Plant Myths – That Save You Time and Money

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Robert Pavlis

The popularity of indoor plants has skyrocketed in the last year and so have the myths surrounding them. I have gathered a long list of common houseplant myths to save you the trouble of making mistakes and getting into bad habits. Each myth has a brief description, and where appropriate, a link to a more detailed discussion.

Growing indoor plants is fairly easy if you take some time to research the plant you are growing and follow some basic rules. Don’t get sucked into internet hype about new ways to deal with problems. Experienced gardeners keep things simple.

Common Houseplant Myths That Save You Time and Help Plants Grow Better
Common Houseplant Myths That Save You Time and Help Plants Grow Better, photo by Proline

Myth #1: Plants Grow Faster in Big Pots

Plants are genetically programed to grow at a certain rate. Better light, adequate water and temperature, and more fertilizer can speed up this process a bit, but it’s mostly driven by genetics. The plant does not even know they are in a pot so why would it affect the growing process?

A bigger pot does have more soil and therefore more room for root growth, but plants only grow the roots they need to support the above ground part of the plant.

Microbe Science for Gardeners Book, by Robert Pavlis

Other related myths:

“A small plant in a pot that’s too big is going to feel intimidated by that huge amount of soil” – that’s silly. All of our indoor plants come from the wild were they grow in huge amounts of soil.

“The plant will try to grow roots to fill out the whole space but a small plant won’t be able to sustain that much root growth.” Simply not true. No plant has ever died because it grew too many roots.

If you want a plant to grow faster focus on its environmental requirements, not on the pot size.

Myth # 2: Water With Distilled Water, Not Tap Water

Distilled water and RO water (reverse osmosis) is pure water containing no minerals. This type of water is harmful to many houseplants, although a few do prefer almost pure water.

Most tap water will not harm plants. If the tap water has a high alkalinity (i.e. hard water) it can harm some plants. In this case you can treat it, or mix it with rainwater, distilled water or RO water to reduce the alkalinity.

Tap water can contain high levels of sodium which is anything over 50 ppm. This can be natural sodium in your water or it can be sodium added by a water softener using sodium chloride. You can find out what your natural sodium level is from your municipal water service. If your water is naturally high in sodium, dilute it as described above for high alkalinity.

If you have a water softener, the cold water taps in the kitchen, and all outdoor taps should bypass the water softener. Use them for watering plants. Don’t use the other taps in your house.

Myth # 3: Tap Water Contains Harmful Chlorine

This is a very common myth without any basis. Municipalities treat their drinking water with either chlorine or chloramine.

Chlorine is an essential nutrient for plants so a small amount is good for them. Science has determined that chlorine or chloramine levels above 150 ppm can be toxic to plants. The World Health Organization suggests using no more than 5 ppm in drinking water and most tap water is under this level. So clearly neither chlorine nor chloramine are an issue.

Myth # 4: Let Water Sit Overnight Before Using It

Some people do this to allow it to de-gas oxygen, others to allow the chlorine to dissipate. Neither of these are required.

It is a good idea to use water that is at room temperature. If you draw cold tap water, let it sit for a few minutes to warm up, but there is no benefit for it to sit longer than that.

Myth # 5: A Strict Watering Schedule is Best

A lot of houseplant advice recommends watering weekly. This is just bad advice.

For a new gardener who is not familiar with plant growth, watering on a schedule is appealing since you can simply follow a rule. The problem is the rule almost never works. You should water when the soil needs to be watered and that is related to how quickly it dries. This drying process depends on many factors including, pot size, plant size, temperature, humidity, amount of light etc. Every plant in every home is different, so a schedule never works.

Stick you finger in the pot. If it is dry, water. If it is wet, don’t. Once you get comfortable with this, you can make small adjustments depending on specific plant needs.

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Myth # 6: Wilting Leaves Indicate They Need to Be Watered

Leaves wilt when they are not getting enough water and there are two common causes for this; not enough watering and too much watering.

Too much water leads to root rot and then the plant has no way to absorb water, so leaves go limp. Wilting leaves only show that there is a problem; it doesn’t identify the problem. It could be something completely different or it might be related to watering, in which case it could be too much water or too little water.

Myth # 7: Succulents Only Need a Tiny Sip of Water

Common advice says to water succulents less than other houseplants. Many interpret this to mean that you should only add a small amount of water each time you water and that is not correct. What it really means is that you should water less often so they dry out between waterings. It also means the plant likes a well draining soil so include more grit or sand in their soil.

When you water, water thoroughly, then leave it alone until the soil is completely dry. In summer the dry period can be shorter, especially if you put the plants outside where they get lots of sun. If they come inside in winter and get less light, make the dry period longer.

Myth # 8: Yellow Leaves Indicate a Dying Plant

Yellow leaves can mean your plant is dying, but it can also mean that the plant is doing well.

Plant leaves don’t last forever. They are disposable. In nature, a plant leaf can endure all kinds of damage from infections and insects. Once it has served its purpose, the plant removes most of the nutrients and sugars from the leaf so they can be used in other parts of the plant. This process causes green leaves to turn yellow. It’s a normal process for all plants.

Where and how the leaves turn yellow tells you something about the plant. If it is the lowest leaf, it is probably nothing to worry about since these are also the oldest leaves. If it is an upper leaf, the plant has a problem. It could be a watering issue, a fertilizing issue or a pest problem. In phal orchids the top leaf turns yellow when the plant has crown rot.

Many people blame yellow leaves on over watering, but that is just an uninformed guess.

Myth # 9: Sick Plants Need Plant Food

I know we like to treat a cold with chicken soap, but when a plant is not doing well, the last thing you should do is fertilize it. Feeding a plant will not make it better, but it might make the problem worse because excess fertilizer can burn new tender roots.

Sick plants and naturally dormant plants use much less fertilizer. If a plant stops growing, stop fertilizing. Plants can live a very long time without being fed.

Myth # 10: Increase Drainage by adding Stones to the Bottom of Pots

This myth has been around for a very long time, in part because it seems to make so much common sense. Stones or pot chards on their own drain very well, so putting them at the bottom of a pot should increase drainage. But it’s myth – it doesn’t work.

This all has to do with something called a perched water table. Water does not move easily from small soil particles to the larger sized of stones. It will saturate the lower level of soil, before moving lower to the drainage material.

If you need better drainage, mix the material right into the soil. Sand or rocks mixed into soil does increase drainage.

Myth # 11: Make Your Plant Leaves Shiny with Mayonnaise

There are a host of home products people spread on leaves to make them shiny including egg whites, milk, yogurt and vinegar, and there are many commercial products as well. These products may not do any significant harm to plants, but they are also not good for them. Anything that leaves an oily layer will attract dust and maybe even pests. It will clog the stomata openings in leaves, making it more difficult for leaves to exchanges gases with the air, and it reduces the amount of light getting to the leaf.

Leaves do not need to be shiny. Learn to enjoy the natural leaf color.

If you want to clean the dust off, use a soft cotton rag and a bit of water.

Myth # 12: Houseplants Purify the Air in Your Home

This is a common myth and many sites even list the best plants for purifying your air. It is all a myth.

Claims that NASA studied this and proved they work are bogus. The writers of those claims never read the NASA research study (I did), because it does not even mention using plants to clean the air in a home.

For the details on this see: A Garden Myth Is Born – Plants Don’t Purify Air .

Myth # 13: Plants Add Oxygen to the Air in Your Home

If you understand photosynthesis you know that plants give off oxygen. The problem is that houseplants produce so little oxygen, that it does not effectively increase the level in your home. You would needs hundreds of large plants in every room to make even a small change.

Myth # 14: Don’t Keep Plants in the Bedroom at Night

The concern here is that, without light, plants produce carbon dioxide and stop producing oxygen. High levels of CO2 can be harmful.

A lot of people know plants use up CO2 in light and give off oxygen, but few know that plants are using oxygen and producing CO2 all of the time; day and night. But these amounts are so tiny compared to the amount humans use, that they have no net effect. You do not need to remove plants from your bedroom at night.

Myth # 15: Most Indoor Plants Go Dormant in Winter

That is not true. Most indoor plants are native to the tropics where it is warm all year long, so they tend to grow all year long. These areas do have dry and wet seasons, so watering can affect their growth. In temperate climates the amount of light is much reduced in winter and that can slow down growth, but it does not stop.

The home tends to be warm all year long, just like the tropics, so houseplants grow all season long.

Myth # 16: Plants Only Need Water, Light, and Air to Grow

I found this comment, “I’m in the anti-chemical camp. From my experience plants only need water, light and fresh air to thrive”. This is complete nonsense!

Plants need basic nutrients or they can’t grow. Those nutrients don’t have to come from synthetic fertilizer, although that is the best source for houseplants. It can come from organic fertilizer, manure, water, or from the soil – but it has to come from somewhere. This is biology 101!

Plants grow much better, have less diseases and pests, if they get the right amount of nutrients.

Myth # 17: Low Light Plants Do Well in a Dark Corner

Some houseplants are labeled as “low light plants” and they are promoted as not needing much light. These plants will survive with very little light but they will do much better with more light. Plants are very adaptable, and they can survive a long time in poor conditions. It can take many months or even years before a plant dies, but if it does not get enough light it will eventually die.

If you place these low light plants in a bit more light they thrive.

Myth # 18: Some Plants are Just Indoor Plants

There is no such thing as indoor plants. All houseplants want to be outside, in the right growing conditions. What we call indoor plants are plants that can survive in low light, low humidity, and can take the abuse of having their roots confined to a small pot.

Try to put your indoor plants outside for part of the year. They will grow much better and usually flower a lot more.

Myth # 19: Misting Increases Humidity

Misting does increase the humidity around a plant but it only lasts for a few minutes. You can see this for yourself. Mist your plants and see how long it takes for the water droplets to dry. Once they are gone, the higher humidity is also gone. Unless you are prepared to mist every 15 minutes, this does nothing to raise humidity, but it might increase fungal diseases.

Myth # 20: Pebble Trays Increase Humidity

Pebble trays do not increase the humidity around plants
Pebble trays do not increase the humidity around plants

As water evaporates from the tray it does increase the humidity right above the tray, and a small amount might even reach the top of the pot, but your plant is left high and dry – quite literally. Humidity trays do not work. You can see from the above diagram that at 7 inches above the tray, the humidity level is raised 1%, which is of no benefit to plants.

Placing plants in an enclosure like an aquarium does increase the humidity, but this environment is only suitable for special plants that grow well in high humidity. It will cause diseases for most plants.

Myth # 21: Used Potting Soil Should be Discarded

What should you do with used potting soil? Many people suggest that you should throw it away, or add it to the outdoor garden because it is “all used up” and it “contains disease organisms”.

The first thing to understand is that potting soil is not really soil. It is usually peat, coir or wood based with a few added amendments like perlite. These materials do decompose over time, but they don’t get old.

Diseases are normally not a problem. Let’s face it, fungal and bacteria spores are everywhere in the air and after a few days your new potting soil is covered with them. If you had a very serious disease it might make sense getting rid of old potting soil, but then you probably need to replace the soil in all your plants. To be honest, I have never seen such a disease.

If you have very hard water, the salts in it do precipitate out and form a white crust on the surface of the soil. This becomes hard to wash out and it can be detrimental to plant roots. In this case scrape off the top couple of inches of soil and discard it. The rest can be reused.

With a few exceptions, there is no good reason for replacing used potting soil and it can be used for many years. One exception would be orchids since they won’t grow well in potting material that is decomposing. But the old orchid media could be used for other types of houseplants.

Myth # 21: Don’t Repot in Winter

For some strange reason some online sources say you should not repot plants in winter; that does not make any sense. In fact, winter might be the best time to repot.

In winter, the temperatures are lower, light levels are lower, especially for people living farther away from the equator. Many plants slow down their growth or even go dormant. Repotting at this time will damage the plants less than if it’s done while they are actively growing.

Think about outdoor plants. We move perennials and trees in spring and fall when they are dormant. We plant bulbs when they are dormant. Nobody recommends moving them in active growth, so why would they suggest doing that with houseplants?

To be honest, you can repot indoor plants any time you want; summer or winter. Just water them correctly after you repot.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

18 thoughts on “21 Common Indoor Plant Myths – That Save You Time and Money”

  1. It might be good to add one little disclaimer: “in the hobby of plants, there are exceptions to every rule (minus the rules of the international code of Binomial Nomenclature)” 😉

    Reply
  2. Distilled and RO water are NOT harmful to plants. They just won’t supply minerals. Minerals are available from soil, compost and other organic materials, and fertilizers. Plants do not get most of their minerals from water.

    While most commercial potting mixes — as you state — lack any real soil, traditional mixes contained them. For all my plants, I make up my own mix of equal parts peat, perlite, compost, and real soil (from my garden).

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    • I think there are a couple of cases to consider.
      If the potting media contains enough fertilizer, it will compensate the lack of salts in distilled or RO water, and they can be used.
      If the potting media does not contain enough fertilizer, the distilled and RO water can draw some nutrients out of the roots. I am not sure how big of a problem this is for most media and plants, but it can be a problem for orchids.
      It is also common to use a fertilizer that does not contain micornutrients, and then the water can be the main source for these. Depending on the fertilizer being used, the water can also be a main source for calcium and magnesium. https://aggie-horticulture.tamu.edu/ornamental/greenhouse-management/treating-irrigation-water/

      Adding soil solves these kind of problems, and I also add soil to outdoor potted plants.

      Reply
  3. This is a great list, just one comment about the used potting soil. I totally agree with re-using most of the time, but can think of one disease issue that would cause me to discard it – basil downey mildew. Basil in containers seems particularly prone to it and it’s soil borne.

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  4. Hi, Robert:

    As a Master Gardener, I led a workshop for local garden clubs for several years, and am gratified to see from what you wrote, that I was accurate in what I said. Covid 19 has halted all garden club gatherings but maybe I can lead one on Zoom in the near future.

    Since Christmas is almost here it might be timely to dispel one more myth: Poinsettias are not poisonous. I researched this for my garden club newsletter. It seems that in the 30’s in Florida, a child died and her parents said she had chewed a poinsettia leaf. No autopsy was ever done, there is no record whether the child had a serious disease, so the myth grew that the poinsettia killed her. It is true that poinsettia stems and leaves contain a bitter milky substance which you’ll probably spit out. It may nauseate you but it will not kill you. However, poinsettias must be kept out of reach of pets–they could be nauseated to the point of losing their digestive processes, and could die.

    Rae Wade

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  5. You may have covered this in a previous post, but Myth #1 also brings to mind that I have always been quite suspicious about advice to serially pot on young plants into containers one size bigger. It seems like an enormous hassle with, for example, tomato seedlings, to pot them on three or four times before they go into their final containers. I can understand gradually moving them into bigger containers if indoor surface space is limited before the weather warms up, but if you have sufficient space, is there any reason not to just prick seedlings out into a container that they can be in until it’s time for them to go outside? I like to direct sow whenever possible, but there are some plants that have to get an indoor head-start in my climate. However, potting-on every few weeks strikes me as likely to be a waste of time.

    I’m a relatively new gardener currently without a garden, so I haven’t really had much opportunity to go against conventional wisdom in my gardening yet. However, I’m hopefully buying my first house with a garden in the coming months and am keen to avoid falling for too many gardening myths!

    Reply
    • I almost added this one and may still add it. This has been studied and there is no benefit to moving plants through a series of slightly larger pots. They will grow better if you go to the large pot right away.

      This is not done commercially mostly because of a lack of space and the cost of water/fertilizer. If you are growing seedlings under a light, space is still an issue, but if you have space – go big.

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  6. Myth # 8 states that “once it [a leaf] has served its purpose the plant removes the nutrients and sugars from the leaf so it can be used in other parts of the plant”. As an interesting aside, it is my understanding that palms are harmed if the browning/yellowing fronds are removed before they are totally spent…as in crispy critters…precisely for this reason. Removing yellowing/browning fronds too soon weakens the plant and allows disease to enter, thus shortening its life. The Naples (Florida) Botanical Garden quite strictly prohibits the early removal of palm fronds unless falling fronds might be hazardous to humans walking under them.

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  7. I seldom repot houseplants only if they get so pot bound that it is difficult to keep them watered. Over the years I have had problems with nutrient deficiencies on palms. According to Ornamental Palm Horticulture (Broschat and Meerow; p 94): “In container-grown palms, Fe deficiency is often associated with old, badly degraded and poorly aerated potting substrates. If a palm is to remain in a container, this degraded substrate should be completely removed and rinsed from the root ball and the palms replanted with fresh substrate.” No control group and I tinkered with multiple variables at the same time (like using a palm fertilizer which has a relatively high content of Mg and K) but after repotting, my Rhaphis palm greened up and still looks good two years later. The palm had been in the same soil for probably ten years before repotting, with just some occasional additions as a topdressing.

    On small plants in a big pot. I believe that it’s easier to water if the plant is in proportion to the pot–that is, the soil dries out more evenly between waterings. So I would go from a 3 inch diameter pot to a 5 inch or 6 inch, but not an 8 inch or 10 inch. My concern being that the soil in the center of the pot where the roots are absorbing water dries out, while the soil at the edge (in plastic) stays wet.

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  8. Do Calathea and other Prayer Plants actually need low mineral or distilled water? I’ve always been told that and am not sure if they’re some of the exceptions.

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