034-Gardening Myths BUSTED, Pt. 1 with Linda Chalker-Scott

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As gardeners, we are always looking for tips and tricks to keep our plants healthy and make our gardens look as beautiful as possible. But have you ever wondered if the advice you’ve taken from someone is based on science? How do you know which is the good? Do some remedies do more harm than good? The fact is, even established advice is, sometimes, just one of many common garden myths.

Today Dr. Linda Chalker-Scott dispels some of the most common gardening myths and reminds us that there really aren’t any miracle products, including Epsom salts.   We’ll also find out how to save money and learn about native soils that are full of beneficial fungi. The following commentary is derived from Linda’s responses to questions provided by subscribers to our joe gardener email list.

Planting Following Moon Phases

Timing the planting of your seeds and crops, as well as other gardening activities to coincide with different phases of the moon may date back to the Egyptians or Babylonians but extensive research by scientists today shows us that there really isn’t anything that ties plant responses to moon phases.

What is affected by the phase of the moon are insects, particularly the ones that have night cycles. So, if there were a pollinating insect or a pest insect this would affect your plants, and one might surmise that it was because of the phase of the moon.  But there doesn’t appear to be a direct effect of gardening according to moon phases.

Still, a lot of people subscribe to this practice of planting by the phases of the moon, without really knowing why.  Maybe they are just good gardeners, or maybe we just haven’t figured out how to test what it is and how to test this unknown factor.

Linda is never one to say never because science is constantly changing and maybe in the future, we’ll figure out what it is we can’t measure yet that affects.  But for now, there is no science behind the benefits of gardening by the moon phases.

Adding Epsom Salts

A lot of people want to know if Epsom salts are the perfect fertilizer. And, is it great for adding to the planting hole when you plant tomatoes or other plants?

This is something that is relevant for production agriculture but not for home gardeners unless a soil test tells you otherwise.

While we associate Epsom salts with positive things like soaking our feet at the end of a long day and feeling silky smooth, this doesn’t have anything to do with how it works in the soil.

Take a Soil Test. A soil test (contact your local cooperative extension service for information) is the most accurate way to determine what nutrients your soil is lacking or if there is too much of a particular nutrient.

Epsom salts are really magnesium sulfate, two chemicals that are required nutrients for plant growth but, it is not a complete fertilizer since it lacks nitrogen, phosphorous and potassium.  Most home gardens are not deficient in magnesium.  So save your Epsom salts for your bath.

Taking it one step further, when you test your soil find out what the levels are for magnesium and calcium.  If there is an imbalance, your soil may have too much calcium or potassium.  This imbalance can make it difficult for roots to take up magnesium.

The solution is not to add more magnesium but to address the toxicity of the soil.

Mycorrhizal Fungi

There is a lot of conversation about the benefits of adding mycorrhizal fungi to your soil.  There’s good science about the benefits of these fungi.  And, your soil is a wonderful repository for spores of mycorrhizal fungi, especially if you have woody plants, (trees and shrubs).


common garden myths on mycorrhizal fungi

There’s good science about the benefits of mycorrhizal fungi. And, your soil is a wonderful repository for spores of it, especially if you have woody plants, (trees and shrubs).


If you feel you need to do something, take a handful of your native soil from underneath your well-established trees and shrubs and sprinkle it around new plantings.  This way you won’t have to buy the spores, and while it probably won’t do any good, it won’t do any harm.  Otherwise, save your money.

Eggshells, Coffee Grounds, & Banana peels

Does putting a tablespoon of eggshells in the bottom of a planting hole or banana peels around the base of a plant have any benefit?

Will eggshells help prevent blossom end rot?

If your soil has too much magnesium, it makes it hard for the plant to take up calcium. And not enough calcium is the cause of blossom end rot. If there is an imbalance in the soil, this is what needs to be addressed.

Once again, a soil test will provide you with good information.

What you want to know is whether your soil has enough calcium because that would be the reason to use the eggshells.  And while they will break down over time, there are better sources of calcium like gypsum.

Does adding coffee grounds to the soil help plants?

The answer is yes, but you have to be super careful.  Coffee grounds are a great source of nitrogen.  They’re about 10% nitrogen just fresh out of the pot.  But use caution with how much you add because they also have a lot of chemicals that can be harmful if you add too much.

Use them with your mulch layer and make sure that the coffee grounds only make up 20% of your mulch or what you add to your compost pile.

Bananas are a great source of potassium, and the peel has a certain amount, but it breaks down very slowly.  Instead, why not add the peels to your compost pile and then you won’t have to dig up squishy peels in your garden.

Compost Tea

Does compost tea improve soil or ward off disease?

Compost teas are traditionally used as liquid fertilizers, but their effectiveness at warding off disease and insects has not been validated by scientific research in large part due to the variability among different batches of the compost used to make the tea and different sources.


Vermicompost Tea

The best way to deliver compost nutrients to plants is direct, as compost. Here, a concentrated solution of vermicompost tea at 10:1, harvested from vermicompost effluent.


While composted organic material makes a great mulch, research by soil scientists has found that there is virtually no difference between using compost tea and using water, regarding plant response or soil nutrient content.

But if you consider just the compost you’ve got this product that is alive with microbes (a lot of them are beneficial and beneficial nematodes too). Then you leach water through it, and you collect that water which is a weak nutrient solution with some microbes (good bacteria) but no food.

Instead, use compost as a mulch and let mother nature brew the tea.

So, every time it rains, or you irrigate you’ve got the slow drip going through of microbes and of nutrients, and their food source is sitting right there.

Another thing to consider is that compost is organic material and improves the soil if it’s part of the mulch layer, you will improve the structure of the soil.

Compost tea does none of this.  It’s water and water is important, but it doesn’t do the great things for soils that compost will.

Vermicompost tea: Compost that goes through worms promotes plant growth, but with the tea, it is in a diluted form so you would have to use a very concentrated form to see any differences.  For this reason, it is more effective to use vermicompost in the same way you use compost.

Synthetic Fertilizer on Good Bacteria

Does nonorganic fertilizer kill good bacteria in the soil?

If you look at a bag of commercial fertilizer, it has nitrogen, phosphate and potassium sulfur.  They are just elements and won’t kill microbes.  What kills microbes are compacted soils or other things that are harmful to life in general.

If you apply too much fertilizer salt buildups will be toxic to the microbes but will also probably kill your plants.  Normal applications of synthetic fertilizers (follow the directions on the bag, more is not better) will not kill good bacteria.

Transplant Fertilizer & Vitamin B1

Is there any benefit to using transplant fertilizers with vitamin B1?

No, plants make their own vitamin B1. The most important thing to add to the planting hole is roots, soil, and water.  Another way to save money.

As for bio-stimulants added to help plants thrive, they are mostly made up of water.  The scientific research does not support using them.

Fresh Wood Chips & Nitrogen Depletion

We’ve all been faced with the decision about whether to accept the “fresh” free wood chips we get from having trees taken down or from a local arborist looking to unload them.

Is it safe to use fresh wood chips for mulch? Will they leach nitrogen away from the soil?


Arborist wood chips used for mulch

One of Linda’s favorite natural solutions to so many gardening challenges can be addressed with fresh arborist wood chips. They do not deplete nitrogen when used as mulch.


It is a myth that fresh wood chips used for mulch will leach nitrogen from the soil. Not only that, you will get a significant amount of nutrients from those materials breaking down during the first month.

The deeper the mulch, the better.

Diseased wood chips should not be a problem if you use them as mulch, but if you are concerned, you could compost them first (but they would lose a lot of nutrient value).

However, don’t amend the soil with fresh wood chips because they will deplete nitrogen from the soil.

And, you may not want to use fresh wood chips if you are germinating seeds in your vegetable garden, although there has not been any research to validate this.

Treated Pallets & Pine Needle Mulch

Don’t use wood from treated pallets. They may have heavy metals or other chemicals.  The same is true for any wood debris from home construction. Since you don’t know if it has been treated, it’s best to avoid it.

As far as the concern that using pine needles for mulch will make the soil too acidic, it will have some effect but not enough to worry about.

You can always test the soil to measure the pH and plan accordingly.

Amending the Planting Hole

Amending the soil is one of those agricultural practices that we have incorporated into our gardens and landscapes, but we now know enough about soil science that it is not necessarily the best thing to work the soil and mix in amendments.

The goal is to get your roots established in the native soil. If you dig a hole and amend the soil in a small area, roots are likely to stay in the amended soil and then there are problems with the soil in the hole and the soil that surrounds it interfacing which means water and air can’t move through the soil.


Backfilling planting hole with native soil

Backfilling the planting hole.


When it comes to tilling or not, the best way to get organic matter incorporated into the soil is to lay it on top of the soil and let nature do the work, even in heavy clay or compacted soils.

By applying a thick (up to a foot deep) layer of mulch on top of the soil, you can accomplish soil building that is pretty incredible.

Taking your lessons from what happens in nature is the smartest way to do it.  This is true not only for trees and shrubs but perennials too.

If your soil is such that your perennials won’t grow in it, consider growing them in containers.

To Till or not to Till

There is a lot of research coming out now that looks at the difference between conventional and organic methods. With a “No-till” organic approach, you don’t disturb the macro-fauna that resides in the soils, beneficial spiders and those things are going to help with pest insects.

In a “no-till” approach, you don’t destroy the mycorrhizal networks.

Water will take the nutrients and microbes into the soil.  Worms come up, and moles are nature’s rototillers, bringing all the good stuff back down. They incorporate the organic matter at a sustainable rate.  Just keep adding organic matter from the top, and it will work its way down.

The bottom line is the more you preserve the soil structure, the more natural pest control you will have and the happier gardener you will be.

The best way to prepare a soil bed whether it’s for trees, shrubs, vegetables or annuals, and perennials is to mow the weeds down and then put on about one foot deep of arborist wood chips.

This completely preserved soil structure preserves soil life and all the benefits it offers.  The thick woody layer keeps light out, killing weeds. The advantage to using the wood chips versus plastic or cardboard is that the water and oxygen permeate through the wood chips.

Once the weeds die you can remove the wood chips, and you will have a friable soil that is ready for whatever you want to plant.

Links & Resources

Episode 035: Gardening Myths BUSTED, Pt. 2 with Linda Chalker-Scott

Episode 036: Gardening Myths BUSTED, Pt. 3 with Linda Chalker-Scott

The Myth of Pathogenic Wood Chips

The Myth of Compost Tea Part 1: Pest Control

The Myth of Compost Tea Part 11: Disease Suppression

The Myth of Compost Tea Part 111: Disease Suppression

The Myth of Coffee Grounds

Miracle, Myth or Marketing Epsom Salts 

Gardening in Washington State fact sheets

The Informed Gardener webpage

The Gardener Professors blog

The Garden Professors Facebook page

The Garden Professors Facebook group

GGW Episode 207  Dispelling Garden Myths- Linda Chalker-Scott

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About Joe Lamp'l

Joe Lamp’l is the creator and “joe” behind joe gardener®. His lifetime passion and devotion to all things horticulture has led him to a long-time career as one of the country’s most recognized and trusted personalities in organic gardening and sustainability. That is most evident in his role as host and creator of Emmy Award-winning Growing a Greener World®, a national green-living lifestyle series on PBS currently broadcasting in its tenth season. When he’s not working in his large, raised bed vegetable garden, he’s likely planting or digging something up, or spending time with his family on their organic farm just north of Atlanta, GA.

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