Treated Wood and Your Raised Bed Gardens
Introduction
Questions have been asked about the use of pressure treated
wood in raised bed vegetable gardens. Various universities have studied
CCA-treated wood in agricultural applications and found no indication
of problems. Most recently, the County Extension of Texas A&M reviewed
this matter and concluded, "...that arsenic was not leaching from timbers
used in raised bed gardens varying in age from 6 months to 9 years of
age." Nevertheless, the Hickson Corporation initiated a test program in
1992 to evaluate this use in more detail.
Test Program
Three raised bed structures were constructed from 2" x 12" Southern
Pine: one was made with Wolmanized®
pressure treated wood and one with Womanized® Extra weather resistant
lumber. These structures were divided into individual bins, so that the
bottom and all sides of a bin were of the same material, i.e., all untreated
or all treated. The bins were filled with potting soil (Majestic Professional
Growers Mix) and various vegetables then planted. An automatic sprinkler
watered the vegetables twice weekly for 15 minute periods. After twelve
weeks, portions of the vegetables were harvested and analyzed for CCA
components. Several vegetables were also obtained at a local grocery store
and analyzed as well.
Vegetable Analysis, Dry Basis, mg/KG (parts per million)
| Vegetable | Untreated Wood | Wolmanized Wood | Wolmanized Extra Wood | Store Purchase |
|---|---|---|---|---|
Chromium | ||||
| Carrot | 3.5 | 1.5 | 1.9 | 1.3 |
| Okra | 1.2 | 1.1 | 0.2 | -- |
| Pepper | 0.5 | 0.9 | 0.9 | -- |
| Cucumber | 1.9 | 1.2 | 0.5 | -- |
| Tomato | 1.1 | 0.4 | 3.5 | 0.6 |
Copper | ||||
| Carrot | 11.8 | 9.3 | 9.6 | 3.6 |
| Okra | 5.1 | 5.1 | 2.7 | -- |
| Pepper | 6.9 | 3.8 | 0.5 | -- |
| Cucumber | 4.2 | 9.5 | 5.1 | -- |
| Tomato | 3.4 | 7.8 | 0.5 | 6.2 |
Arsenic | ||||
| Carrot | <0.8 | 2.2 | 2.9 | 2.7 |
| Okra | <0.8 | <0.8 | 1.5 | -- |
| Pepper | <0.8 | 0.5 | <0.8 | -- |
| Cucumber | 0.5 | <0.9 | <0.5 | -- |
| Tomato | <0.8 | 0.5 | 2.1 | 3.7 |
Summary
Testing of Wolmanized pressure-treated wood in raised bed garden
applications has shown that there is no uptake of the metal constituents
into the vegetables