Rooting Out the Truth: Debunking Common Gardening Myths Part 2

Think you know the secrets to a perfect garden? In part two of our “Gardening Myths” series, host Erin Hoover continues to separate fact from fiction on some widely believed plant remedies and techniques.

From adding coarse materials in pots to improve drainage and painting wounds on trees and avoiding the use of wood chip mulches to keep nitrogen in the soil—are these tricks worth your time, 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 two of this two-part series covers these gardening myths:

• Gardening Myth #6: Putting a Coarse Textured Material in the Bottom of a Container Improves Drainage
• Gardening Myth #7: Painting Wounds on Trees Helps Seal Disease Out
• Gardening Myth #8: Wood Chips Rob Nitrogen from Soil
• Gardening Myth #9: Young Trees Need to be Staked 
• Gardening Myth #10: Trees Need to Be Planted as Deep as Possible and Square Holes Improve Trees’ Growth 

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.

• Rooting Out the Truth: Debunking Common Gardening Myths Part 1 – Episode 35
  
• Gardening Myth #6: Putting a Coarse Textured Material in the Bottom of a Container Improves Drainage
  • WSU Publication on container drainage.
  • Drainage in Containers
• Gardening Myth #7: Painting Wounds on Trees Helps Seal Disease Out
  • WSU Publication on Wound Sealers
  • Tree Wound Paints
• Gardening Myth #8: Wood Chips Rob Nitrogen from Soil
  • https://s3.wp.wsu.edu/uploads/sites/403/2015/03/wood-chips.pdf
  • Using Arborist Wood Chips as a Landscape Mulch (Home Garden Series)
• Gardening Myth #9: Young Trees Need to be Staked 
  • https://s3.wp.wsu.edu/uploads/sites/403/2015/03/staking.pdf
  • Tree Staking | Purdue Extension Forestry & Natural Resources
• Gardening Myth #10: Trees Need to Be Planted as Deep as Possible and Square Holes Improve Trees Growth 
  • Are My Trees Buried Too Deep?
  • Planting Trees and Shrubs in the Landscape (Home Garden Series)

[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 The Evergreen Thumb episode 36.

Today we’re jumping into part two of our episode about debunking gardening myths.

[00:01:00] If you missed part one of this episode, I’ll put a link in the show notes so that you can find that. In part two, we’re covering adding drainage medium to the bottom of pots, painting wounds on trees, whether wood chips rob nitrogen from the soil, whether or not you need to be staking trees, and the idea of planting trees deeply to help develop healthy roots.

Gardening Myth #6: Putting a Coarse Textured Material in the Bottom of a Container Improves Drainage

[00:01:19] All right, so let’s just jump right into myth number six. Uh, I did one through five on the first episode and this episode is six through ten.

Adding a drainage medium to the bottom of pots. So this would be like putting a layer of gravel or rocks or marbles in a pot before you plant it.

[00:01:40] And for this, I have an article from Nebraska Extension in Dodge County and the University of California, Santa Clara County Master Gardeners.

Putting coarse textured material in the bottom of a container is believed to improve drainage. That’s the myth. And it seems intuitive that it should work, but it doesn’t.

[00:02:01] When you put a layer of material in the bottom like gravel, it reduces the usable depth of the pot, and water does not move easily from the fine-textured potting soil to that coarse-textured material. Water moves through the soil because of gravity and capillarity.

So, the pores in the potting soil allow the water to be pulled downward via gravity, and only when the whole pot is saturated does water move downward by gravity.

[00:02:31] So, gravel and other coarse materials don’t have capillary pores, so the downward movement of water or the drainage of water will stop when it encounters that coarse layer and it will just remain in the band of soil, just at the bottom of the soil.

[00:03:00] If the drainage holes in your container are too big and you’re worried about all the potting soil washing out, you can place, you know, a little shard of clay or put a piece of newspaper in the bottom of the pot, but you’ve got to avoid the larger coarse material that will prevent the pot from draining.

[00:03:10] Again, according to the University of Nebraska, the soil stays saturated at the very bottom and then that water in that saturated zone is normally at the bottom of the pot where it can drain out if it’s excess, but when it’s on a layer that’s different, that water gets hung up and can’t percolate out.

[00:03:34] It doesn’t even have to be a coarse material. Any layer of difference will affect the flow of water through that pot, whether it’s, I don’t know, golf balls or marbles, or whatever.

[00:04:00] So that pretty much covers a drainage medium in your potted plants.

Gardening Myth #7: Painting Wounds on Trees Helps Seal Disease Out

For this next one, I consulted Tim Kohlhoff, um, who I mentioned earlier on, the pine needle study, since he’s an arborist and what he thought some of the bigger myths were around trees.

[00:04:07] And one of the ones he mentioned was painting wounds on trees. I always thought this was something that was necessary until recently.

When you’re pruning, I was taught that you want to seal that to keep disease out. And it turns out that many of these are petroleum-based products, and what wound dressings really do is seal in moisture, which then causes decay.

[00:04:36] They can serve as a food source for pathogens. They can prevent wound wood from forming. Wound wood is, you get like almost like a bubble of bark that tries to go around the end of the wound. That is wound wood, and it can inhibit compartmentalization. So that is what the tree actually will compartmentalize itself and so if there is anything that gets into that wound, it can compartmentalize that and keep it from passing on to the rest of the tree.

[00:05:11] And wound dressings usually will eventually crack, then expose the tree to pathogens because the tree hasn’t been able to protect itself.

Wound dressings do not stop rot, they do not prevent the um, introduction of decay organisms. Trees have natural methods of healing and branches have protection zones that limit infection.

[00:05:32] That’s where I say it was compartmentalization. So when you cut off the branch, the trunk of the tree or the, the main part of the plant, will compartmentalize and cut itself off from that wounded branch to prevent any disease from passing into the rest of the tree. Studies have also shown that wound dressings can be phytotoxic.

[00:05:54] Studies also show that they did not promote wound closure, they did not inhibit wood discoloration, and some wound dressings actually harmed trees. Some tree paints actually have solvents in them that can kill the cambium tissue in the tree, which then further weakens the tree.

Now, there have been some studies that show certain types of dressing are beneficial when used on certain species against certain infections.

[00:06:25] Things like perennial canker in stone fruits, they did a study where shellac was beneficial in reducing the infection. Latex paint was used in the same study and was effective but only for short periods of time before it cracked and let the fungi gain entrance.

Wound paints have been used to help reduce the spread of oak wilt and Dutch elm disease by preventing the insect vectors of these diseases from having access to the wounded tissue.

[00:06:53] Fungicides applied to pruning cuts and or wounds have been used to control some diseases. There’s only one class of fungicide registered for that use and it’s to protect grapevine and stone fruit wounds against several fungal, trunk, and canker diseases.

[00:07:21] So basically what this research shows is that there are some very use case-specific applications for fungicide wound dressings, but for the home gardener, it is more likely to do harm than good if you are painting wounds on your trees.

Gardening Myth #8: Wood Chips Rob Nitrogen from Soil

Okay, the next one is that wood chips rob nitrogen from the soil. This is one that I have been aware for quite a while and I’ve been trying to dispel myself. I have another article from Linda Chalker-Scott talking about wood chip mulch.

[00:07:47] Um, and there is also a WSU extension publication, uh, on using arborist wood chips as landscape mulch. Wood chips can be a great addition to ornamental landscapes, um, but aren’t necessarily the best mulch choice, say, for a vegetable bed, just because of the amount of time it takes for them to break down, and it’s a use case issue where you want to make sure that you’re using the best mulch for the situation.

[00:08:14] The direct benefits of any landscape mulch benefit the soil, the plants, the system, and the people. So arborist wood chips represent one of the best mulch choices for trees and shrubs. A 1990 study evaluated the landscape mulch potential of 15 organic materials including grass clippings, leaves, compost, yard waste, bark, and wood chips.

[00:08:36] Wood chips, um, were one of the best performers when it came to moisture retention, temperature moderation, weed control, and sustainability.

In many areas, arborist wood chips are free. We get at least one 10-yard load a year just from when they come out to prune the trees away from the power lines.

[00:08:56] All I had to do was walk up to them and work with them and give them my address. Then a couple of days later, they showed up with a load.

Now, it’s also important not to confuse wood chips with sawdust or bark mulch, like the, the dyed and shredded mulch you get from most landscape supply companies. Sawdust tends to compact and create a, a crusty layer that affects the ability for water to percolate into the soil.

[00:09:23] There are some concerns people have, concerns like woody mulches will acidify soils, there can be leach allelopathic chemicals, or that diseased trees can infect healthy trees, have all been unfounded.

One of the reasons that wood chips make such a great mulch is that they don’t leach nitrogen from the soil, but they do reduce the nitrogen levels at the soil mulch interface. Because of this, it reduces seedling survival because they don’t have enough nitrogen, so they suppress weeds.

[00:09:55] Now, many studies have demonstrated that woody mulch materials increase nutrient levels in soils or associated plant foliage overall. What Dr. Chalker-Scott says, her hypothesis is that there is a zone of nitrogen deficiency, like I just mentioned, that inhibits the weed seed germination, but it doesn’t have an influence on the established plant roots below the surface because they can’t pull the nitrogen out of the soil.

[00:10:29] And this is another reason not to use wood chips, say, on vegetable gardens, because those plants typically don’t have deep extensive root systems.

Gardening Myth #9: Young Trees Need to be Staked 

Okay, myth number nine I want to talk about is staking trees. To stake or not to stake? According to Purdue University, that is the question. And no is likely the answer.

[00:10:54] Trees tend to establish themselves quite well in normal situations. Support systems, like staking and guying, are in most cases unnecessary and can even do more harm than good to the tree. Movement in the wind is actually crucial to helping younger trees develop strong root systems and strong trunks and structurally be balanced.

[00:11:18] There are rare conditions when staking or guying or some other form of support is required, but these are very specific use case scenarios typically related to larger trees in high wind areas or things like that. There are a lot more risks than benefits to staking or guying a tree.

Guying is where you’re connecting wires and supporting them in multiple directions on the ground, whereas staking is, you know, connecting the trunk to a post of some sort.

[00:11:55] And that’s usually used for smaller trees or container stock, uh, whereas guying is for larger trees that are transplanted and it provides three points of attachment to give support.

The biggest problems with staking trees is that they are staked too high, too tightly, or for too long, which will all cause damage to the tree.

[00:12:20] Depending on the medium used to support the tree, it can cause significant damage. If it’s left on too long, the bark will actually grow around the wires. Wires can cut into the tree. And as I said, they can prevent the tree from forming a good supporting root system because it doesn’t have to hold itself up.

[00:12:44] So I also have a document from Linda Chalker-Scott who also addresses this. A lot of retail nurseries will instruct customers to stake trees regardless of the need for doing so and those instructions can sometimes be incorrect as well as unnecessary. Once the trees are installed, especially if they’re installed, say, by a landscape company or even by a property owner, there’s little aftercare for these trees.

[00:13:16] So, especially with a landscape company, staking materials won’t be removed at the appropriate time, if ever, unless you have a management plan as part of the agreement when that tree’s being installed.

A lot of nursery stock are staked in the pot for stability, and a lot of people don’t realize that the staking material should be removed when you are transplanting.

[00:13:38] Trees that are staked improperly will grow taller, but they will have a decreased trunk caliber, and they develop less trunk taper or even a reverse trunk taper. They develop the xylem unevenly, they have smaller root systems, they suffer rubbing or girdling injuries from the stakes and ties, and they’re actually more likely to snap in a high wind after the stakes are removed.

[00:14:06] Bare root trees are more likely to require staking than bald burlap trees in a pot. The materials, if you’re going to stake a tree, the materials should be flexible and allow for movement all the way down to the ground so that the trunk taper develops properly. Place the stakes as low as possible and no higher than two-thirds of the height of the tree.

[00:14:34] All staking material needs to be removed after the roots have been established. This can be as early as a few months but should be no longer than one growing season. Any materials that are used for permanent tree protection should never be attached to the tree. Those guidelines are all from Dr. Linda Chalker-Scott, and I will include her document in the show notes as well.

Gardening Myth #10: Trees Need to Be Planted as Deep as Possible and Square Holes Improve Trees Growth

[00:14:59] Our final gardening myth is kind of a mix of a couple, but it has to do with planting trees. So there is a myth that trees need to be planted deep to help develop healthy roots, and there’s also been a newer concept going around lately that where planting trees in a square hole is somehow better for the growth of the tree.

[00:15:25] The first one I want to address is burying the trees deep. When you plant a tree, you need to be able to see the root collar at the base of the tree. This is where the trunk flare and the root collar meet at the right above the roots where the roots begin. That should be visible on all trees, regardless of where it’s planted.

[00:15:49] Trees are not like tomatoes. Tomatoes are one of the very few plants that you can plant deeper, and they will form new roots from the stalk of the plant. Trees do not work like this. 99% of plants do not grow that way, the way tomatoes do.

So what happens if that root collar is not visible, it can shorten the life of the tree because it can actually lead to decay of the bark, which can introduce disease, it will rot the whole trunk through, there’s a lot of possibilities that can affect the tree.

[00:16:25] And part of this is because the trunk wood and the root wood are very different in their makeup. When trunk wood is buried in soil or mulches, it stays wet, which impacts the exchange of gases such as oxygen and carbon dioxide that are required to keep the phloem alive. The phloem is the plant tissue that’s just under the bark that transports the food made in the leaves to the other parts of the tree.

[00:16:51] Over time, a buried trunk flare will begin to die and decaying fungi will move in. So this dieback inhibits the translocation of food and also inhibits the tree hormones communicating within the tree that are impacted causing the tree to not harden off in preparation for winter. What also comes into play here is the idea of mulch volcanoes.

[00:17:16] It’s the same idea. You’ll see these trees that have these mounds of mulch up the trunk of the tree, and that basically does the same thing. It creates higher moisture levels around the tree wood that can cause rot and decay and shorten the life of your tree. So a lot of this information comes from Penn State University Extension.

[00:17:44] And they have a great website that explains how to tell if your trees are buried too deep. Something to consider is that many times trees are too deep in the container already when you bring them home from the nursery. So it’s important when you’re planting the tree, wipe away that soil to see where that trunk flare or root collar starts.

[00:18:03] And if you need to, you know, set some extra soil in the center of the hole for the roots to sit on so that it sits properly in that hole.

WSU has a great publication in their home garden series all about planting trees and shrubs in the landscape. How to dig a hole, how to set the tree in the hole, how big the hole needs to be, how deep to set the tree or shrub in the hole.

[00:18:27] And I will link to that as well. That is free to download off WSU’s website. They do address a number of problems to planting and the number one uh, problem is planting too deep.

Uh, the next problem is dense root mass on container-grown plants and how that can cause root girdling, which also can affect the stability and health of your tree. They also do address staking after planting in that publication as well.

[00:18:52] I hope I was able to give you enough evidence to dispel some of these common gardening myths. If there are more gardening myths you are curious about, send me a message and I will see if I can either prove or disprove whether or not they are accurate.

[00:19:15] So I want to take a moment to thank Tim Kohlhoff for his input on this episode and acknowledge that I did use a lot of resources from Dr. Linda Chalker-Scott, who’s a WSU horticulturist, and I will include links to, I have at least two resources for each of these myths, and I will include them all in the show notes, where you can read up and see the research that I found.

[00:19:40] If you have any questions about a specific myth, feel free to email me at hello@theevergreenthumb.org.

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.

[00:20:02] 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.

[00:20:20] 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.

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.

[00:21:04] If you enjoyed today’s episode and want to stay connected with us, be sure to subscribe to future episodes filled with expert tips, fascinating stories, and practical advice.

Don’t forget to leave a review and share it with fellow gardeners to spread the joy of gardening.

Questions or comments to be addressed in future episodes can be sent to hello@theevergreenthumb.org.

[00:21:25] The views, thoughts, and opinions expressed by guests of this podcast are their own and do not imply endorsement by Washington State University or the Master Gardener Foundation of Washington State.