The Q&A Archives: treated lumber in garden

Question: Would treated lumber affect a wisteria vine leader from growing normal gowth? How about leaf size? The vine seems to have stopped growing on the leader. Would there be chemicals that would cause this do you think? I built a beautiful pergola for this Texas Purple Wisteria but it doesn' seem to be happy.

Answer: There are two sides to the story concerning the safety of pressure treated wood in gardens. One says they are safe, citing studies showing little or no leaching of arsenate into the soil. The other side has its own studies and says it does leach at dangerous levels. So, I lean to the cautious side and recommend gardeners not use pressure treated wood, especially for food plants. Try cedar, redwood, hemlock, plastic wood or cement blocks as alternatives. Since you've already invested in the treated lumber and built your pergola, you could dig down where the wood touches the soil and line the area with plastic to reduce the risk of the chemicals leaching into the soil. After you've done that, prune out the affected plant parts to encourage healthy new growth. Your wisteria needs regular deep soakings during the summer months to help it establish a healthy root system.

Best wishes with your landscape!

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