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Posted on August 11th, 2014 in Drought, Forestry, How To, Plants | No Comments »

mulch at base of tree

Although fresh chips from tree pruning and removals look great for mulch and compost, there are some hidden issues. First, fresh wood chips can be very acidic (sometimes down around a pH of 4) which can be detrimental to plant growth. Also fresh chips have a high C:N (carbon to nitrogen ratio), and it must borrow nitrogen from the soil to help the decomposing process. So mixing the chips with the soil can actually reduce fertility for a while. Both of those can be problems for plants trying to grow in a bed mulched or mixed with fresh chips. Ideally, the newly ground chips should compost properly for a full year. If nitrogen fertilizer is added to the soil/mulch mix, it can speed up the process.

The effects of wood chips as mulch involve mainly the surface of the soil, which means it’s mainly shallow-rooted plants like perennial and annual flowers that would run into fresh wood chip trouble. This includes serious chlorosis and other health issues involving establishment and development. Deeper-rooted trees and shrubs are less likely to be affected as much; however, they are subject to the effects of the poor C:N ratio. I would suggest removing as much of the chips as possible, piling them for composting and replacing with proper soil for perennial growth unless you can wait for a full year to allow the decomposition cycle to be completed. This may help eliminate issues with new plants going into that location.

Mulching Conserves Soil Moisture, Department of Horticulture and Landscape Architecture
Growing Perennial Flowers, The Education Store (Search keywords to find the resources you need)
Collecting Soil Samples for Testing, The Education Store
Soil and Water Conservation Districts, Indiana State Department of Agriculture
Certified Soil Testing Laboratories, Purdue Department of Agronomy/Extension

Lindsey Purcell, Urban Forestry Specialist
Department of Forestry and Natural Resources

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