I want to cover my raised beds with stucco or a similar material. Which building materials should I use to stay in compliance with organic standards?
Answer: It’s always a good idea to check with your local organic certification agency before applying new materials to currently certified beds or beds that are in the process of becoming certified. There are a few options to choose from for building materials and a few different ways to approach making your raised beds more aesthetically pleasing. First of all, before applying any material to the outer surface of these raised beds you will need to apply a buffer, such as a metal lath backing, around the wood. This will allow for another material (such as stucco) to be applied around the wood. To ATTRA’s knowledge, there is no metal lath on the market that is prohibited from being used around organic production. Next, you might consider placing a weather barrier around the wood, although this may not be necessary depending on the type of stucco or cement-like material you use to cover it. If you do want to use a weather barrier, keep in mind that many contain products that are not permitted for use with organic production. For example, black felt paper is commonly used as a weather barrier under house siding. It consists of about 50 percent asphalt and 50 percent organic felt. However, asphalt is petroleum-based material and is prohibited from contact with soils in organic production. The wooden material of the raised beds may create a large enough barrier between the soil and felt paper to prevent soil contamination, but it would be up to an organic certifying agency to determine if this type of barrier is adequate. Regarding applying stucco or cement-like material around the raised beds, lime plaster and cement contain materials like hydrated lime (calcium hydroxide) that are restricted or prohibited from use as soil amendments in organic production. However, if you are careful enough not to get materials like cement or hydrated-lime on the garden beds themselves, once the materials have hardened and a buffer (the metal lath) exists between the soil and the material, it should not affect the crops. Lime plaster has less embodied energy compared to cement stucco. Lime plasters are durable, but depending on the amount of rain in your area, may need to be touched up every year or two. As far as a weather barrier behind the stucco, it would make sense to use one if you are going to use cement-based stucco, but you should not use one with a lime plaster because it needs to breathe. A useful resource for learning about plasters and other building materials is www.buildnaturally.com/EDucate/Articles/Lime.htm. For more information about organic materials and compliance, see the ATTRA publication Organic Materials Compliance at https://attra.ncat.org/attra-pub/summaries/summary.php?pub=157. For information about wooden building materials, see the ATTRA publication Pressure-Treated Wood: Organic and Natural Alternatives at https://attra.ncat.org/attra-pub/summaries/summary.php?pub=73.