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Be careful with fresh wood chips in the garden
Jessica Walliser
Jessica Walliser | Saturday, April 5, 2008
Questions: I had a large pin oak tree taken down in late fall. After the stump was ground, I was left with a rather large pile of sawdust/chips, etc. Can this be used for mulch and if so, where• I have a rather large garden, 40 feet by 20 feet, where I grow a multitude of crops with excellent success. I would imagine these chips, etc., would be acidic. I guess I can use them around my hemlocks and "rhodies" planted around my house. I was thinking of using this mulch on the outside perimeter of my garden. Would this be OK, or would the resultant leaching into the soil ruin my garden?
Answer: The good news is that you can use those new wood chips. The bad news is that I'm going to be pretty specific about where you can use them safely. There are a number of reasons why you don't want to use those fresh wood chips in the vegetable or flower garden.
First, because they are actively decomposing, they are generating heat. Using large quantities of these fresh chips can burn plant foliage. Secondly, there may be a resulting soil pH change after using these chips depending on how many you add. Fresh wood leachates can have a pH as low as 4, which is quite acidic and could potentially result in undesirable soil conditions. This pH change usually only affects the soil down to a few inches, so it is more harmful to shallow-rooted plants like herbaceous perennials, annuals and vegetables; it isn't so much of a factor for deeper-rooted trees and shrubs. Thirdly, and most importantly in my mind, fresh wood chips are very high in carbon, and in order for them to fully decompose, nitrogen needs to be involved. This necessary nitrogen is pulled from the underlying soil. Eventually, that nitrogen will be returned to the ground when the chips are completely broken down, but in the meantime, you are stealing this essential nutrient from your plants.
That being said, there are a few places where it is safe to use fresh wood chips. The compost pile is a great place to put them to work. Because they are so high in carbon, you'll need to mix them with half as much grass clippings and/or manure by volume. Toss in a cup of lime for every four wheelbarrows of wood chips to help neutralize the pH. Let the pile compost for a year or two (turn the pile whenever you can -- ideally once or twice a month). The resulting product can be used anywhere in the garden and makes a beautiful soil amendment. It also is safe to use a few inches of fresh wood chips around evergreens and other acid loving plants like rhododendrons, azaleas and boxwoods. Keep the chips a good three or four inches away from the trunk of the plants to ensure the heat of decomposition doesn't harm the bark.
Horticulturist Jessica Walliser, co-author of the books "Grow Organic" and "A Gardener's Journal," can be heard from 7-9 a.m. Sundays on KDKA Radio's "The Organic Gardeners." You can also find her teaching at Phipps Conservatory and Botanical Gardens, where she has been a faculty member for more than 12 years.
https://triblive.com/x/pittsburghtrib/lifestyles/homegarden/s_560706.html
Jessica Walliser
Jessica Walliser | Saturday, April 5, 2008
Questions: I had a large pin oak tree taken down in late fall. After the stump was ground, I was left with a rather large pile of sawdust/chips, etc. Can this be used for mulch and if so, where• I have a rather large garden, 40 feet by 20 feet, where I grow a multitude of crops with excellent success. I would imagine these chips, etc., would be acidic. I guess I can use them around my hemlocks and "rhodies" planted around my house. I was thinking of using this mulch on the outside perimeter of my garden. Would this be OK, or would the resultant leaching into the soil ruin my garden?
Answer: The good news is that you can use those new wood chips. The bad news is that I'm going to be pretty specific about where you can use them safely. There are a number of reasons why you don't want to use those fresh wood chips in the vegetable or flower garden.
First, because they are actively decomposing, they are generating heat. Using large quantities of these fresh chips can burn plant foliage. Secondly, there may be a resulting soil pH change after using these chips depending on how many you add. Fresh wood leachates can have a pH as low as 4, which is quite acidic and could potentially result in undesirable soil conditions. This pH change usually only affects the soil down to a few inches, so it is more harmful to shallow-rooted plants like herbaceous perennials, annuals and vegetables; it isn't so much of a factor for deeper-rooted trees and shrubs. Thirdly, and most importantly in my mind, fresh wood chips are very high in carbon, and in order for them to fully decompose, nitrogen needs to be involved. This necessary nitrogen is pulled from the underlying soil. Eventually, that nitrogen will be returned to the ground when the chips are completely broken down, but in the meantime, you are stealing this essential nutrient from your plants.
That being said, there are a few places where it is safe to use fresh wood chips. The compost pile is a great place to put them to work. Because they are so high in carbon, you'll need to mix them with half as much grass clippings and/or manure by volume. Toss in a cup of lime for every four wheelbarrows of wood chips to help neutralize the pH. Let the pile compost for a year or two (turn the pile whenever you can -- ideally once or twice a month). The resulting product can be used anywhere in the garden and makes a beautiful soil amendment. It also is safe to use a few inches of fresh wood chips around evergreens and other acid loving plants like rhododendrons, azaleas and boxwoods. Keep the chips a good three or four inches away from the trunk of the plants to ensure the heat of decomposition doesn't harm the bark.
Horticulturist Jessica Walliser, co-author of the books "Grow Organic" and "A Gardener's Journal," can be heard from 7-9 a.m. Sundays on KDKA Radio's "The Organic Gardeners." You can also find her teaching at Phipps Conservatory and Botanical Gardens, where she has been a faculty member for more than 12 years.
https://triblive.com/x/pittsburghtrib/lifestyles/homegarden/s_560706.html