Fill around a red cedar - Ask Extension
I am putting fill around a large western red cedar and am wondering if that will harm the tree. We are on the coast where it is hard to kill plants bu...
Knowledgebase
Fill around a red cedar #858877
Asked February 10, 2024, 12:41 PM EST
I am putting fill around a large western red cedar and am wondering if that will harm the tree. We are on the coast where it is hard to kill plants but I have the uphill side under up to 2 feet of fill and would like to put up to 14 inches up 10 feet out on the downhill side.
Douglas County Oregon
Expert Response
This is a bad idea.
One of the most common problems we find on urban trees is buried root crowns. The root crown is the transitional region at the base of the trunk where the trunk becomes the root system. The root crown is typically marked by the root flares, the large buttress roots at the base of the tree. This area should always be exposed to air and not covered with dirt or mulch, but often mature trees on urban sites have had backfill placed around the trunk as a result of construction or landscaping. Young transplants are often planted too deep. A buried root crown is an easy target for insects and pathogens that can weaken or even kill the tree. Additionally, over time buried root crowns can develop a condition known as girdling roots, where roots from the tree roots grow back around the buried trunk. As these roots age and swell they put pressure on the phloem, the vascular tissue beneath the bark. This interferes with the transport of sugars in the tree and can lead to root and canopy dieback and the eventual death of the tree.
Raising the grade or soil level over existing roots can have an even greater effect on the future growth and survival of existing trees. When soil or any type of fill is placed over the existing root system, it causes a reduction in the oxygen supply to the tree roots and slows down the rate of gas exchange between the roots and the air in the soil pore space.
Both oxygen and water are essential to the growth, development and nutrient uptake by the roots. Many of the soil organisms also utilize the water and oxygen in their normal growth processes. Lack of oxygen in the soil may result in accumulation of noxious gases and chemicals detrimental to good growth. When this occurs, the feeder roots fail to develop, the root system and the above-ground portion of the tree begin to decline. Many factors (including tree species, depth and type of fill, drainage, soil structure below the fill and the general vigor of the existing tree) have a determining influence upon the time it takes for the above-ground symptoms to appear. Thus, it might take anywhere from several months to as much as 3 to 5 years before tree death would occur.
If a fill has been in place long enough for visual symptoms of tree deterioration to occur, little can be done to save the tree. In cases where the fill has been made recently or where no serious damage has occurred, some corrective action can be taken.
If the increase is less than 12 inches, it is possible to remove soil around the tree trunk down to the original soil level for a radius of 2 feet beyond the trunk. A dry well should be installed around the trunk to hold the fill soil in place. Starting about two feet out from the dry well, holes should be drilled or dug every 2 feet beneath the branch spread. A 6-inch plastic pipe should be inserted and then filled with coarse gravel to allow free air and gas exchange in the root zone. This will usually suffice for a shallow fill.
Here is a great publication that may be useful:
One of the most common problems we find on urban trees is buried root crowns. The root crown is the transitional region at the base of the trunk where the trunk becomes the root system. The root crown is typically marked by the root flares, the large buttress roots at the base of the tree. This area should always be exposed to air and not covered with dirt or mulch, but often mature trees on urban sites have had backfill placed around the trunk as a result of construction or landscaping. Young transplants are often planted too deep. A buried root crown is an easy target for insects and pathogens that can weaken or even kill the tree. Additionally, over time buried root crowns can develop a condition known as girdling roots, where roots from the tree roots grow back around the buried trunk. As these roots age and swell they put pressure on the phloem, the vascular tissue beneath the bark. This interferes with the transport of sugars in the tree and can lead to root and canopy dieback and the eventual death of the tree.
Raising the grade or soil level over existing roots can have an even greater effect on the future growth and survival of existing trees. When soil or any type of fill is placed over the existing root system, it causes a reduction in the oxygen supply to the tree roots and slows down the rate of gas exchange between the roots and the air in the soil pore space.
Both oxygen and water are essential to the growth, development and nutrient uptake by the roots. Many of the soil organisms also utilize the water and oxygen in their normal growth processes. Lack of oxygen in the soil may result in accumulation of noxious gases and chemicals detrimental to good growth. When this occurs, the feeder roots fail to develop, the root system and the above-ground portion of the tree begin to decline. Many factors (including tree species, depth and type of fill, drainage, soil structure below the fill and the general vigor of the existing tree) have a determining influence upon the time it takes for the above-ground symptoms to appear. Thus, it might take anywhere from several months to as much as 3 to 5 years before tree death would occur.
If a fill has been in place long enough for visual symptoms of tree deterioration to occur, little can be done to save the tree. In cases where the fill has been made recently or where no serious damage has occurred, some corrective action can be taken.
If the increase is less than 12 inches, it is possible to remove soil around the tree trunk down to the original soil level for a radius of 2 feet beyond the trunk. A dry well should be installed around the trunk to hold the fill soil in place. Starting about two feet out from the dry well, holes should be drilled or dug every 2 feet beneath the branch spread. A 6-inch plastic pipe should be inserted and then filled with coarse gravel to allow free air and gas exchange in the root zone. This will usually suffice for a shallow fill.
Here is a great publication that may be useful:
https://aggie-horticulture.tamu.edu/earthkind/landscape/protecting-trees/
Hope this helps!
