Rooting Out the Truth: Debunking Common Gardening Myths Part 1

Think you know the secrets to a perfect garden? In part one of our “Gardening Myths” series, host Erin Hoover separates fact from fiction on some widely believed plant remedies and techniques. From Epsom salts and blossom end rot to houseplants as oxygen machines and the acidic magic of pine needles—do these tricks actually work, or are they myths holding you back? Tune in as we break down the science behind these gardening tips to help you grow smarter.

Part one of this two-part series covers these gardening myths:

• Gardening Myth #1: Houseplants Purify the Air in Your Home
• Gardening Myth #2: Pine Needles Acidify Your Soil
• Gardening Myth #3: Blossom End Rot Signifies a Soil Calcium Deficiency
• Gardening Myth #4: Epsom Salts are a Gardening Cure-All
• Gardening Myth #5: Watering on Sunny Days Causes Sunburn on Leaves

As a homesteader, Erin has turned her own property into a small, thriving farm. She grows veggies, tends to fruit plants, and raises livestock, all while following permaculture principles to keep things as sustainable as possible. Her focus these days is on finding new uses for native plants, figuring out ways to feed her animals from her land, and growing her own food.

When she’s not working on the homestead or recording The Evergreen Thumb, you’ll find Erin out exploring Washington’s mountains, forests, and beaches—always looking for ideas and inspiration to bring back to her garden.

• Gardening Myth #1: Houseplants Purify the Air in Your Home
  • Potted Plants and Indoor Air Quality at Nature.com
  • Greening Your Space: Caring For House Plants with Ann Amato — Episode 008
• Gardening Myth #2: Pine Needles Acidify Your Soil
  • Myth vs. reality: What’s the truth behind some common gardening practices?
  • Ponderosa Pine Needles: Techniques for Successful Composting
• Gardening Myth #3: Blossom End Rot Signifies a Soil Calcium Deficiency
  • Blossom End Rot Fact Sheet
  • The Epsom Salt Myth
  • Harvesting the Best: Tomato Tips for Washington Gardeners — Episode 027
• Gardening Myth #4: Epsom Salts are a Gardening Cure-All
  • Turfgrass specialist discusses rumored benefits of Epsom salt in gardens – UGA Today
  • https://s3.wp.wsu.edu/uploads/sites/403/2015/03/epsom-salts.pdf
  • WSU Publication – Epsom Salt Use in Home Gardens and Landscapes
• Gardening Myth #5: Watering on Sunny Days Causes Sunburn on Leaves
  • The Myth of Hot-Weather Watering
  • Can water burn plant leaves?

[00:00:00] Erin Hoover: Welcome to The Evergreen Thumb, your go-to podcast for up-to-date research-based horticulture and environmental stewardship knowledge to help you grow and manage your garden. Produced by Washington State University Extension Master Gardener Volunteers and brought to you by the Master Gardener Foundation of Washington State.

[00:00:16] I’m your host, Erin Hoover, a WSU Extension Master Gardener since 2015 and a certified permaculture designer and modern homesteader.

WSU Master Gardener volunteers are university-trained community educators who have been cultivating plants, people, and communities since 1973. Are you ready to grow? Let’s dig into today’s episode.

[00:00:44] Welcome to episode 35 of The Evergreen Thumb.

This is part one of a two-part series of myth-busting. We are going to debunk some gardening myths, but first, we need to go over the December gardening calendar.

December Gardening Calendar

Being December, there’s a lot less going on in the garden, of course, so it’s going to be kind of a short list, but first up for planning is if you plan to purchase a living Christmas tree, be sure you have enough space to plant it in an appropriate location.

[00:01:20] It is likely going to be a large tree when it’s mature. Don’t keep living trees inside for more than a week if possible, as indoor heat and low humidity in the winter are very stressful for conifers. And be sure to plant your tree as soon as you’re able.

Another planning idea is to observe how water moves or doesn’t move, if the case may be, and plan how you’re going to make changes to manage that water flow.

[00:01:48] Be sure to take lots of pictures so that you’ll remember later what the problem was and how you want to manage it. This is especially a good time to do during heavy rains so that you can see where those drainage problems are.

Tilling, ditching, and French drains may be short-term solutions, but if you have a serious water issue, I recommend considering rain gardens or bioswales as a longer-term solution.

[00:02:14] In maintenance, you want to check your stored flower bulbs, vegetables, and fruits for rot or fungus issues, and then discard anything that is showing signs of rot.

If you live in a particularly dry area, uh, you may need to water every six to eight weeks with a deep soaking to keep plants from drying out.

[00:02:37] Uh, if it is particularly windy and you haven’t had any rain or snow in quite a while, this could be especially important. In western Washington, it tends to be damp enough that there, and there’s enough, uh, condensation and humidity that it’s not an issue on the west side of the Cascades.

For planting, in western Washington, it’s actually a good time to plant trees and landscape shrubs, um, provided that the ground is not saturated, um, because digging in that, uh, very wet soil can actually damage the soil structure and make it very compacted.

[00:03:13] But, if the ground, if it’s not freezing and you have some trees and shrubs that you would like to get into the ground and let them get established before spring, this is a good time to do that.

Check for rodent damage around the base of trees and large shrubs. Remove weeds to prevent rodents from using that as hiding places.

[00:03:32] Rodents may also use mulch around the bases of trees as cover. So avoid mounding mulching materials too high on the tree. Sometimes these are called mulch volcanoes and if they are too high, they can also cause the bark to rot and compromise the health of the tree.

For houseplants and indoor gardening, if you bring home poinsettias for the holidays, be sure to protect them from the cold. Place them in sunlight, but don’t let the leaves touch the cold windows. Be sure to fertilize them with a regular houseplant fertilizer to help maintain their leaf color.

[00:04:00] Monitor all of your houseplants for adequate water and fertilizer. These requirements generally are lowered in the winter, so you won’t need to water them as often or as deeply, um, but they do still require some water.

[00:04:27] And that pretty much covers it for December. Like I said, it’s a pretty short list, so now we will get into our episode.

Top Ten Gardening Myths

Welcome to The Evergreen Thumb. I’m your host, Erin Hoover, and today I am going to bust the top 10 gardening myths. There really are a lot more than 10 gardening myths, but I’ve chosen 10 that I could find a lot of good research to back them up.

[00:04:52] I will share all of those sources with you in the show notes on our website, and I will provide a link, uh, for those. So there are a lot of gardening myths out there and over the years a lot of various gardening myths have spread via whether it’s, you know, through generations of how people have done things or on social media.

[00:05:14] So, and some of this goes back to the episode I did not too long ago about how to know you have reliable sources for your gardening information. And I’ll link to that one in the show notes as well. A lot of these myths seem harmless, but in reality, they can lead to very poor plant health. They waste your time, or they can even do environmental harm.

[00:05:36] So understanding what’s true and not is going to help you to become a more successful and sustainable gardener. So, we’re going to debunk some of the more common gardening myths and shed some light on the science behind these gardening practices.

Gardening Myth #1: Houseplants Purify the Air in Your Home

So, the number one myth that I want to talk about, and these are not in any particular order, is that houseplants can purify the air in your home.

[00:06:00] Back in episode eight, um, I did an episode with Ann Amato and we actually discussed this in our discussion about houseplants. We talked about whether or really do improve air quality.

I have a study from The Journal of Exposure Science and Environmental Epidemiology that what it comes down to is, is the plants do not improve indoor air quality and also there’s an article by the American Lung Association that talks about this as well, and I will link to both of those.

[00:06:30] There are a lot of benefits to house plants. But purifying your indoor air is not necessarily one of them.

This concept goes back to a study that NASA conducted in 1989 when they were researching ways to clean air in space stations. The study showed that plants did clean the air in a very closed, limited environment.

[00:06:54] The problem with taking this study and applying it into our homes is that our indoor environments, our homes are not like space stations. They’re literally a chamber that is very almost sterile. You know, it’s very minimalist. It’s very, it’s a lot smaller than most homes. So, it doesn’t really translate into real-life settings.

[00:07:18] So, and the sample sizes that NASA used in this study are often so small that there’s really not a way to apply them. And one quote, from the, uh, United States Environmental Protection Agency regarding the NASA study said to achieve the same pollutant removal rate reached in the NASA chamber study would require having 680 plants in a typical house.

[00:07:43] So that gives you an idea. I mean, yes, they will clean the air, but they do it on such a small level that it takes a lot of them to have an impact.

Another thing to consider is that for people, especially sensitive populations, in many ways plants can contribute to unhealthy air conditions, whether it be mold in the soil. Um, if you use pesticides or fertilizers, they become part of your environment.

[00:08:05] So these are also things to take into consideration when choosing to have houseplants.

Gardening Myth #2: Pine Needles Acidify Your Soil

All right, so the second gardening myth I have is about pine needles acidifying your soil. Recently I saw on a Facebook group that someone was going to mulch their blueberries with pine needles, too, because blueberries like more acidic soil, and they believed that the pine needles would make the soil more acidic.

[00:08:47] The resources I have for this, one of these is an article written by Steve McConnell, who’s a regional extension specialist in forestry for WSU extension, and Tim Kohlhoff, who has been a guest on the podcast before. He is the urban horticulture coordinator for WSU Spokane County extension and is an arborist.

[00:09:09] They actually did a great study in Spokane about composting pine needles. If you live in Eastern Washington, especially in Spokane, you know, there’s a lot of ponderosa pines, and down needles can be a concern because they can be a fire hazard.

A lot of people believe because ponderosa pine trees grow in acidic soils and the needles themselves are acidic, that the pine needles will actually acidify the soil or damage their plants if they use it as a mulch on plants that don’t necessarily need acidic soil.

[00:09:42] They set up a research and demonstration project at the Spokane Extension Office to determine how ponderosa pine needles might make a useful carbon source for compost.

[00:10:04] They used three different methods to try to compost down the needles. So different ages and treatments of the needles to determine what was going to work best based on what a typical home gardener might do.

After leaving these to compost, they said that all three treatments resulted in usable compost within three months. Then the final level of pH for all of them was very close to neutral. The takeaway from this particular experiment was that ponderosa and pine needles are carbon rich and they make great compost, but once they are composted, um, it is pH neutral compost.

[00:10:29] When they, as they break down, the acidity is neutralized. Pine needles in their whole farm are acidic, but as they decompose, they become pH neutral. So what this means is that, if you use it as mulch, it is not going to harm your plants.

[00:10:55] And if you want to compost it or turn it into your soil, it is not going to acidify your soil if you’re trying to alter the soil for blueberries or rhododendrons or anything like that. I also have an article from Oregon State University. Myth vs reality: What’s the truth behind some gardening practices?

[00:11:13] It’s true that pine needles have a pH between 3.2 and 3.8 when they fall off a tree, and it is possible you might see a slight drop in soil pH if you were to turn them into the soil right away, but the change would not be significant enough to damage the plant.

[00:11:37] If you use them as mulch, they will eventually break down, but they do fairly slowly. Putting them in your compost pile would probably be more efficient. Um, if you were looking to create nutrients or add nutrients and use these needles as nutrients, if you’re looking to suppress weeds, putting them on whole should work great.

The third myth I want to talk about is blossom end rot and calcium.

Gardening Myth #3: Blossom End Rot Signifies a Soil Calcium Deficiency

[00:11:56] I spoke with Alice Slusher recently on episode 27, all about tomatoes, and we discussed this a little bit, the blossom end rot in tomatoes and how blossom end rot is not a soil calcium deficiency.

I’ve seen this in multiple gardening groups online and things like that, that, you know, they say, oh, add, add calcium to the soil, add Epsom salts to the soil and it’ll fix the problem.

[00:12:22] So I have two documents. One is an article by the University of Wisconsin Madison Extension. It’s a disease fact sheet on blossom end rot and then the other one I have is from North Dakota State University is called the Epsom Salt Myth.

Um, and I, so I’m going to kind of combine this with another myth is that Epsom Salt is a garden cure-all. A lot of people think Epsom salts can, can kind of do it all.

[00:12:46] Now, when it comes to blossom end rot, that’s exactly what it sounds like. The blossom end of the tomato starts to turn brown or bruised, um, at the bottom of the fruit. Blossom end rot is caused by a lack of calcium in the fruit.

It can be due to low calcium levels in the soil but more likely it is there’s plenty of calcium in the soil, but it is unavailable for the plant to take up into the fruit because of drought stress or inconsistent watering keeps that calcium from being mobile. It inhibits the calcium uptake.

[00:13:25] The best way to control blossom end rot is to make sure, to avoid too much or too little water. It’s important to water evenly. If you do have rains, you know, don’t water, check the water level in your soil, use mulch to retain moisture during dry periods, and try not to cultivate the soil near the plants, um, because cutting those roots can also affect the uptake of calcium.

[00:13:55] If you think your soil is calcium deficient, it’s best to do a soil test to make sure before you add anything to your soil, more often than not, that there is plenty of calcium in that soil. In fact, using Epsom salt to try to treat blossom end rot will actually make the problem worse because blossom end rot is a calcium issue, but Epsom salt is actually magnesium.

[00:14:22] And so adding Epsom salt to the soil may actually create more rot because magnesium and calcium compete for uptake into the plant. And the more magnesium there is in the soil, the less chance that calcium will be absorbed. This is according to North Dakota State University.

Gardening Myth #4: Epsom Salts are a Gardening Cure-All

[00:14:43] From here, I’m going to go on to the other one I mentioned, that is the idea that Epsom salts are a cure-all. So we’ve just talked about how Epsom salt can actually make blossom end rot in tomatoes worse. But some other things to consider is that, I mean, a lot of people think that Epsom salt is a great quote unquote, natural amendment for your garden.

[00:15:05] And there are a lot of claims that it’s beneficial to tomatoes and peppers and roses. And we talked about tomatoes. There is no research to show that any of those things are true. And like I said, because it is magnesium rather than calcium, you’re actually adding significant amounts of meat and magnesium to your soil.

[00:15:27] And if your soil is not deficient in magnesium, you could be doing more harm than good. That was from the University of Georgia.

And then I also have an article from Dr. Linda Chalker Scott, who is a WSU horticulturist and professor at the Puyallup Research and Extension Center, it is possible that adding Epsom salts can relieve magnesium deficiency, and there are a number of crops that can suffer from magnesium deficiency, vegetable crops, but applying a blanket to your vegetable garden is likely to do more harm than good unless you have done a soil test to know that your soil is lacking magnesium.

[00:16:13] A lack of soil magnesium is often caused by mineral imbalances in the soil, and they most commonly occur in light, sandy, or acidic soils, although intensely cultivated or intensely producing clay soils can also be magnesium deficient.

If your soil is deficient in magnesium because of heavy rainfall or irrigation leaching the magnesium from the soil, Epsom salts are not going to be of benefit because it is highly soluble in water and is just going to go as pass through the soil with that water, um, instead of staying around long enough to be taken up by the plants.

[00:16:46] The claim is that using Epsom salt with roses can just deter pests like slugs and voles. There have been a number of tests on the chemical controls for flies, grasshoppers, various caterpillar pests, and alfalfa pests, and the research all showed that there is no current research to suggest any insecticidal activity of Epsom salts, and there is no literature that reports the activity of Epsom salts against slugs or voles.

[00:17:21] And then there are other claims that Epsom salt can help seeds germinate, that can help plants grow bushier, produce more flowers, increase chlorophyll production, improve phosphorus and nitrogen uptake, and there really is no scientific basis for most of these claims.

Most seeds contain plenty of minerals to initiate root and shoot growth. That’s the job of the seed. It is biologically complete and has everything it needs in the way of nutrients to do the work.

[00:17:46] As far as making plants bushier, it’s a kind of a term that’s difficult to quantify. As I said, the, because it’s water soluble, oftentimes it passes right through the soil. And if your soil is not magnesium deficient, then it is not likely to have an effect on the size or health of your plant.

[00:18:22] However, plants that are suffering magnesium deficiency can benefit because they may look bushier, quote unquote bushier, because a magnesium deficient plant will drop leaves and then rectifying the deficiency will prevent leaf drop and make the plant look bushier.

[00:18:47] As far as increasing chlorophyll production, this one may actually be true. Magnesium is a physical part of the chlorophyll molecule, and a deficiency of magnesium will cause a reduction in chlorophyll production.

So it’s not necessarily that it increases chlorophyll production, but it provides the nutrients to give the plant enough to adequately do its job. Um, so it’s not producing an excess of chlorophyll or a surplus of chlorophyll.

[00:19:13] If it’s already magnesium deficient, then it has reduced chlorophyll production and you’re bringing balance back to the plant so that it is producing an appropriate amount of chlorophyll.

The idea that Epsom salts can improve phosphorus and nitrogen uptake is not completely unfounded because a plant that is deficient in magnesium will be stressed and less able to utilize other nutrients.

[00:19:37] So again, by bringing balance back to the plant, if it is nutrient deficient if it is magnesium deficient, then the magnesium from the Epsom salt could be of benefit, but excessive amounts of Epsom salt will not increase normal uptake of other nutrients like phosphorus and nitrogen.

So that kind of combined into two. So that was three and four.

Gardening Myth #5: Watering on Sunday Days Causes Sunburn on Leaves

[00:20:01] So 5 is that watering on hot sunny days causes sunburn on leaves. And I have an article here, another article from Linda Chalker Scott. She does a lot of writing on busting these myths. So, I do have a lot of articles from her as a source for some of this information.

If your plants are showing signs of water stress in the middle of the day, then water them because I mean a stressed plant is a vector for disease and you know you want to keep your plants as healthy as possible.

[00:20:36] If you wait until the evening, evening is not the best time to water your plants because it can encourage fungal pathogens. And while there are many elements that can cause leaf scorch on a plant, irrigating with water when it’s sunny is not one of them.

The biggest thing that causes damage to plants is drought, lack of water, and excess water.

[00:20:57] These will affect your plants and have more than water in the heat of the day. Ideally, the best time to water is in the morning when it’s still cool. The biggest reason not to water in the middle of the day is evaporation. It is a less efficient way to water, but it is unlikely to do direct harm to your plants.

[00:21:16] After a drought, salts can be built up in the soil or it can be sprayed from the ocean or other saltwater bodies or, um, road de-icing salts, over application of fertilizers, herbicides, insecticides can always cause salts to build up in the soil. So then when you irrigate, those salts are solubilized and taken up by the plant and can become toxic to the plant.

[00:21:40] Other things that cause leaf scorch can be wind stress, temperature stress, and cold stress. All of those environmental stressors are directly linked to decreasing water availability in leaves.

Urea, which is contained in a lot of fertilizers, can burn foliage and is a very common cause of turf damage. So to prevent leaf scorch, it’s important to have environmental conditions for optimal root health.

[00:22:05] So it’s moisture, oxygen, temperature, and nutrients, and a good plant spacing are all the best ways to keep your plants healthy. And be sure to watch your plants for signs of wilt. If they start to wilt, it’s important to water them. If they pass the terminal wilt stage, no amount of water will save them.

[00:22:24] And be sure that your plant is planted in the right place with its required sun/shade requirements. A shade-loving plant that’s planted in the right place, where it gets too much sun is gonna burn.

So these are all ways to prevent that leaf scorch, but what it comes down to is that leaf scorch is not caused by direct watering on your plants.

[00:22:51] Well, that wraps up part one of our two-part series on busting our top 10 gardening myths.

So for a quick recap, the gardening myths we covered today were the myth of houseplants purifying the air in your home, the second one we discussed was pine needles and whether they will acidify your soil. Number three was blossom end rot and calcium.

[00:23:20] And then we kind of transitioned into Epsom Salts as a cure-all, as well as for blossom end rot. That was three and four. And finally, number five was watering on hot sunny days causing sunburn on your plants.

Join us where we cover the other five of the top ten gardening myths. In that episode, we will cover the myth of adding drainage medium to the bottom of pots for potted plants, the myth of painting wounds on trees, and the myth that wood chips rob nitrogen from your soil.

[00:23:48] And then also we will talk about tree staking and planting trees deeply to help develop healthy roots. So, join us next time.

And, as always, we have all of the documents that I talked about for the research on these myths will be on our website at theevergreenthumb.org or you can find a link in the description for this episode to the show notes directly, and we’ll have links to everything there.

Alright, I hope you found that useful, and maybe I surprised you a little with a couple of these myths. If that’s the case, I’d like to hear about it. Send me an email at hello@theevergreenthumb.org or connect with us on social media. Send me a DM, comment on the post for this episode, and let me know what you think.

Thanks for listening.

Thank you for joining us on this episode of the Evergreen Thumb, brought to you by the WSU Extension Master Gardener Program volunteers. And sponsored by the Master Gardener Foundation of Washington State.

[00:24:58] We hope that today’s discussion has inspired and equipped you with valuable insights to nurture your garden.

The Master Gardener Foundation of Washington State is a nonprofit organization whose primary purpose is to provide unifying support and advocacy for WSU Extension Master Gardener programs throughout Washington State.

[00:25:17] To support the Master Gardener Foundation of Washington State, visit www.mastergardenerfoundation.org/donate.

Whether you’re an experienced Master Gardener or just starting out, the WSU Extension Master Gardener program is here to support you every step of the way. WSU Extension Master Gardeners empower and sustain diverse communities with relevant, unbiased, research-based horticulture education.

[00:25:42] Reach out to your local WSU Extension office to connect with master gardeners and tap into a wealth of resources that can help you achieve gardening success. To learn more about the program or how to become a Master Gardener, visit mastergardener.wsu.edu/get-involved.

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