Too Mulch of a Good Thing

Most Nebraskans know the story of Goldilocks and the 3 bears….Goldilocks goes for a walk in the forest, comes across a house, enters the house and helps herself to the porridge on the kitchen table.  Upon tasting it, she finds out that it’s too hot.  She proceeds to taste some porridge from another bowl and determines that it’s too cold.  Still, she sojourns on and finds another bowl to be just right.  The story repeats itself with chairs to sit in and a bed to take a nap in.  After the bears find her and she wakes up from her nap, she runs out the door.  We’re not sure exactly what happens after that, but it sure makes for a good classic story for reading time with young children.

 

The porridge, chairs and beds are good icons for the “just right” recommendation of applying mulch in the landscape.  It’s common to see all 3 iterations of mulch quantity in various landscape settings, too much, not enough (or any at all) and just right.

 

What’s too much?  Often described with the term “mulch volcano”, when mulching material is placed on the soil around the tree as well as a foot or more up on the trunk itself, as depicted in the attached photo, it’s too much.  In these situations, excessive moisture is retained on the bark tissue, causing it to soften and degrade.  When this occurs, the conductive vessels underneath are susceptible to dehydration and reduced capacity to transport water and nutrients throughout the tree.

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What’s not enough?  When mulch is not applied at all, or in a thin, uneven layer, it’s not present in sufficient quantity to provide benefits for the tree.

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What’s just right?  Just right is similar to what Mother Nature provides – a 2-3 inch layer of bark chunks, chips, fruits, flowers, stems, leaves and buds – that fall to the soil and cover the area of active rooting for the tree.  It’s ok for the mulch to rest lightly against the trunk, but in most cases, it would be better to pull it away from the trunk a few inches or so to prevent bark softening.

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Applying mulch in this way will help achieve the objectives of moisture retention, weed suppression and protection from mowers and other lawn maintenance equipment for the tree.

John Fech
Horticulture Extension Educator at Nebraska Extension
John Fech is a horticulturist with the University of Nebraska-Lincoln and certified arborist with the International Society of Arboriculture. The author of 2 books and over 200 popular and trade journal articles, he focuses his time on teaching effective landscape maintenance techniques, water conservation, diagnosing turf and ornamental problems and encouraging effective bilingual communication in the green industry. He works extensively with the media to extend the message of landscape sustainability, making over 100 television and radio appearances each year.
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