Pressure-Treated Lumber In Vegetable Garden & Growing Kale

Question:

I’m looking to build several raised beds for a vegetable garden. Is pressure-treated lumber safe to use?

Answer:

  • Gardeners have been using pressure-treated lumber for decades for posts, retaining walls, and raised beds.
  • Old-time gardeners will remember the popularity of railroad ties for projects. Unfortunately, Railroad ties were treated with pentachlorophenol and creosote, toxic wood preservatives.
    • As the supply of railroad ties diminished, lumber treated with chromated copper arsenate (CCA) became available. It boasted longer life than untreated wood and improved longevity than redwood.
    • As we became more concerned with these chemical health issues, the Environmental Protection Agency (EPA)in December of 2003 banned the sale of lumber treated with CCA for residential use.
  • Copper-based wood preservatives were the replacement. The National Gardening Association addressed this change with the following statement: "The newest method for treating wood is Micronized Copper Quaternary (MCQ).
    • It is chemically different than the old CCA treatments. It is made of tiny (micro) particles of copper. These particles are forced into the wood cells or pores during the pressure cycle. Once in, they stay in, also forming a barrier keeping in the quaternary. The leaching of chemicals out of MCQ is practically non-existent, and using the treated lumber for a vegetable bed is safe because the chemicals do not leach out into the soil." It's still the standard today. 
  • A simple precaution would be to line the sides of the bed with plastic sheeting. This preventive barrier would also guard against any leaching from the wood.
  • However, for those who want to grow organic edible, do not use pressure-treated lumber at all. You should choose a different material such as basal blocks or moss rock.
    • 'Wood Acetylation' is a new technology on the horizon. It's a technique that uses acetic acid as in vinegar to make wood resistant to rot and insects. It's hard to say when it will be widely available. 

NOTE: You shouldn't panic if your raised garden beds have arsenic-treated wood. Plants will not take up the arsenic leached into the soil unless the soil is deficient in phosphorous. This shouldn't be a problem if you add additional amendments and vegetable food each season. In addition, you could supplement the garden area with 0-10-10 or Superphosphate, 0-20-0. I also discovered treating wood with canola oil (3 parts), and vinegar (1 part) makes a super wood sealant, protecting wood from borrowing insects, wear, and water.

Question:

 I eat a lot of Kale and would like to grow it in pots. Could you give me some hints on how to grow it successfully?

Answer:

  • There is no reason why you couldn't grow Kale in containers.
  • The biggest issue is the timing. Kale is a cool-weather crop that grows in full sun. When the temperatures get into the eighties, you should move it into afternoon shade. It also 'Bolts' that is it goes to seed quickly with warm temperatures, so you should discontinue growing it during the summer months until the fall.
  • With all different container sizes, you should allow eight square inches of growing space per plant. This then guides you to how many to plant per container.