Landscape Timbers Sustainability

Asked May 20, 2013, 1:45 PM EDT

We have recently moved into a house on the edge of Forest Park, on the south side of Cornell Rd and the north side of a steep, heavily wooded slope. Accordingly it receives little light and lots of rain. We want to build a series of steps, probably about 20, up part of the hill and researched via Google various ways. One way that seems physically easiest it to use PT landscape timbers as frames for steps. However, further Google research indicates that landscape timbers are not pressure treated in the same way as other pressure treated wood. We have two concerns then: 1. how long is such wood likely to last in contact with the ground in this wet, rather dark environment; and 2. is there a chance of harmful chemicals leaching from the wood? I understand that using rock or concrete is a possible solution, but since I plan to do this work myself, wood would seemingly be physically easier. Thank you in advance for your response, Alex Stepick

Multnomah County Oregon

1 Response

Hello and thanks for your question. For untreated wood, longevity for parts contacting the soil is usually in the 5-7 year range. For a few like cedar and redwood, it can be twice as long or more under some circumstances. I am not sure how this compares to chemically treated lumber, the the dealer or manufacturer should have that information for you to help you make your decision. Health information about using pressure treated wood for gardening shows that generally it is not a serious issue. See: http://smallfarms.oregonstate.edu/sfn/w10PressurizedLumber Here is another article from Washington State University looking at some of the hazards, recommending using copper treated lumber rather than the older types using heavy metals, and even considering "plastic" timbers. http://gardening.wsu.edu/library/vege021/vege021.htm . Wood is significantly easier to work with if you are doing your own construction, so I hope this information is helpful. You will need to inspect every year or two to make sure that none of the timbers are failing and be ready to replace parts if this is necessary. Linda