Garden Myths - Learn the truth about gardening

Archive for the Soil Category

Can Leaves be Used to Identify Nutrient Deficiencies?

There are lots of examples of people trying to use plant leaf characteristics to identify nutrient deficiencies in the soil. This seems to make a lot of sense. If the soil is lacking a specific nutrient, it should show up in the plant and it seems to follow that by examining the physical characteristics of the leaf you should be able to identify the nutrient deficiency.

How reliable is this method of diagnosis? Can you really identify a nutrient deficiency in the soil by looking at plant leaves?

Plant Nutrient Deficiency Symptoms by Permablitz

Plant Nutrient Deficiency Symptoms by Permablitz

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Walnuts, Juglone and Allelopathy

The common statement “nothing grows under walnut trees” is not true. “Walnuts produce juglone”, is not entirely true either. “You need to compost walnut wood chips before using them in the garden”, is false. “The allelopathic properties of walnuts are well understood” – definitely not true.

This is a popular subject that is routinely discussed and written about, but the truth around walnut trees is anything but clear.

Black Walnut - Walnuts, Juglone and Allelopathy

Black Walnut – Walnuts, Juglone and Allelopathy

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Sand and Clay Don’t Make Concrete

What happens when you add sand to clay soil? Many people claim that this will make concrete and others say that it results in soil that is easier to dig. How can there be such large discrepancies about something that is so easy to test?

Why is this a problem? Gardeners with heavy clay find it difficult to dig, so they want to loosen it up. Sand is very easy to dig and it makes a lot of common sense to add it, to create a looser soil.

Soil texture triangle - sand and clay soil

Soil texture triangle – sand and clay soil

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Mulch – How Does It Affect Soil?

Mulching the garden is a very common recommendation. Mulch will reduce the number of weeds and it will hold moisture in the soil but how does mulch affect the quality of soil?

There are lots of claims that mulch improves soil but have you ever seen numbers to validate them? I haven’t either. How exactly does mulch improve soil? It should add organic matter, but how much? It should increase the number of microbes, but is this really true? Unfortunately, almost nobody studies landscapes and gardens because no one will fund the work.

Luckily I was able to find one very good research paper that looked at this exact problem.

Effect of fertilizer and mulch on soil, by Garden Myths (based on reference 1)

Effect of fertilizer and mulch on soil, by Garden Myths (based on reference 1)

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Sterile Soil – Does it Really Exist?

There is lots of talk about using sterile soil. Some people even sterilize their soil before they use it. Others buy bags of sterile soil. All of this is done in an effort to reduce pests, diseases and sprouting seeds. This all seems to make a lot of sense but there are a couple of basic questions that one should ask;

  • Does sterile soil really exist?
  • Does sterile soil make a difference to your plants?

 

I’ll deal with the second question in my next post. Today I want to discuss the existence of sterile soil.

Sterile soil

Sterile soil – does it exist?

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