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Girdling Roots and Mulch Volcanoes

Posted July 12, 2020 by Wei Zhang

A recent discussion on facebook prompted me to write this blog about #Girdling #roots and #mulchvolcanoes. These two issues are particularly common problems for urban forestry. They are not the same, but are somewhat connected in that mulch volcanoes promotes girdling roots. I see mulch volcanoes every day outside of our office. After talking to the landscaper while they were "committing the crime" and subsequently our landlord, nothing happened. I wrote facebook post about it:

For newly planted trees, watering is critical for the first 2-5 years depending on the size of the trees. It is because these newly planted trees just lost either up to 90% of its root system when dug up from the tree farms, the automatic irrigation system in nurseries that turns on twice a day, or both. There are many watering prescriptions telling people to provide a certain amount of water per day or per week on the rootball. Together with other common issues with newly planted urban trees (e.g. compacted soils, unfavorable soil pH for the tree species, lack of nutrients, limited soil volume), the moist and nutrient-rich soil inside the rootball (from the growers) promotes girdling roots since the trees are not incentivized to grow roots outward into the surrounding soil.

The correct way is to water the rootball AND the surrounding soil. Watering the rootball is critical for the survival of these trees for the week/month/year, while watering the surrounding soil is critical for the survival and thrival 20 years later.

TreeDiaper® technology, if people follows our recommendations, can help to prevent these problems. First, we recommend TreeDiaper® sizes to be around double of the rootball sizes. So not only the rootball, but the surrounding soils are also watered. It promotes healthy outward root growth. Second, TreeDiaper® has a ring shape with good space between the trunk and the inner rim of the TreeDiaper® treemats. We recommend people mulch along the contour of the TreeDiaper® to make a mulch ring instead of a mulch volcano.

In 2013 when we were looking for a partner to do a field trial of TreeDiaper® treemats (Weed Control and Moisture Conservation Treemat was the name back then), Hanover County Parks and Recreation allowed us to put TreeDiaper® treemats on a number of trees in Taylor Park. It is one of the earliest case studies we carried out during the development of this technology. I revisited the site in June 2019. I intentionally checked the root system. No roots were found growing in circular direction even though maple are one of the species that are most susceptible to girdling roots.

BTW, there was no watering for these maple trees since TreeDiaper® installed. The watering absorbing amount is only about 20% of the original full capacity while the weed control function is 100%. It also protects the trunk from lawn mowers and weed trimmers.

"The TreeDiaper® products have really helped keep our bushes and trees slowly watered over the seasons. They are reasonably priced and delivered very quickly. As we get more trees, we'll order more TreeDiaper®."

- Jim R, Happy Customer