Re: Question about landscaping timbers
Vicki Spurling asked about the wisdom of using "landscape timbers" with
which to let hubby build her raised beds.
In January 1996, I had a professional landscape architectural firm build me
a pair of fabulous raised beds, and they used CCA (an arsenic-based
preservative formula)-treated lumber. This is said to be the big No No in
terms of leaching chemicals into the soil touching the wood of the beds.
I have indeed read some horror stories on the gardening newsgroups about
people getting wildly distorted veggies and having their raised-bed soil
tested and finding bad quantities of poisonous compounds in the soil.
I have NOT had my raised-bed soil tested, but I've grown veggies for 6
seasons now and cannot see any evidence of distorted fruit or stunted plants.
Nevertheless, if you want to use the timbers your spouse has purchased and
not have to worry about this issue, then line the sides of the empty beds
completely with heavy-gauge plastic before dropping the soil mixture into
the beds. Be sure to leave some slack in the way the plastic lies as you
put the soil in. You don't want the plastic to break at all anywhere,
above or below the soil line.
Do not line the bottom of the raised beds with the plastic, however. That
would wreck the superior drainage that makes raised-bed gardening work so well.
Your supplier should be able to tell you what preservative was used to
treat the timbers you bought. If they're slightly greenish-looking (like
mine), it was probably CCA. This material is injected into the timbers
under tremendous pressure. The wood itself is extremely heavy because of
the chemicals inside. I believe that little of the baddies leaches out
over time, but I have not had the necessary soil tests done to prove it one
way or the other. The wood in my beds is holding up beautifully, by the
way. There is some surface cracking (which showed up right away, not just
lately). But nothing is compromised by it.
Occasionally one sees the suggestion that people purchase used railroad
ties for the purpose of building raised beds. That would be, chemically
speaking, no great improvement over the CCA-treated timbers because
railroad ties are preserved using creosote--another baddie.
--Janet
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