A Pressure-Treated Dilemma

Here Comes the Sun...* A recent question from New Hope Community Garden got me thinking about the whole pressure treated wood issue again.  I checked recent research and did some soul-searching and here is what I came up with…

“Dear Sun –what about using treated wood or railroad ties for raised beds.  If we use un-treated wood will we have termites?”

The first question is - do you really need boxed beds?  There are two reasons to box in container beds.

  1. Where space is limited - boxes allow more efficient and intensive plantings.
  2. Easier access for seniors - a 10" or 20" high bed is easier for senior gardeners to work.

Most community gardens utilize a combination of  free-standing raised beds and box beds depending on the space available.  Free-standing beds can be built up with compost and surrounding soil to a height of 8".  This gives you good drainage and soil depth.  You lose some garden space due to the sloping sides but I think this is minimal given the size of the garden that New Hope is planning (1/4 acre or more).  With the space that you all have available I do not think that boxed beds will be cost effective for the whole garden.  The two 20" high  3'x 60' beds we built for seniors at the Mayview Community Garden cost over $600.  Add another $150 if you use treated wood.

The debate over possible health effects of treated wood rages on and is adequately addressed in the two articles I reference here at the bottom.  It really comes down to how much arsenic do you think is safe in the soil where you grow your food?  Even though arsenic migrates only a few inches from treated wood surfaces, the plant’s roots will be in this zone regardless.  When you till or turn the soil this contaminated zone will be mixed into the rest of the soil and, over time, arsenic levels will rise in your garden.

Regardless of how you feel about arsenic in your garden, the continued production and use of CGA treated wood, especially on decks and landscape (where it leaches into the environment) presents a long-term threat to our health my opinion.  That is why the federal govt. called for industry to voluntarily phase out CGA treated wood 5 years ago.  The racks are still full at Home Depot.  So much for voluntary efforts from industry.

Railroad ties are treated with cresote, a highly toxic and carcinogenic chemical and should never be used in gardens or anywhere around your home - period.

Termites are everywhere.  If you use untreated wood, the life of your bed boxes will be 3-6 years.  Termites will not hurt your plants but you will want to keep untreated wood structures at least 12' from your home or storage shed.  I am trying some different organic treatments on the Farm including diatomaceous earth to see if they are effective on termites.

My recommendations would be to

  • Minimize boxed beds to where they are really needed.  Raised free-standing beds are just as effective unless you are really crunched for space.
  • Where you do need boxed beds use treated posts sunk in concrete and painted with sealant. Use untreated boards for the sides.  Try to find salvaged 2"x 6", 8" or 10"s if possible.

Other boxed bed alternatives include...

  • cinderblock walls - (must have masonry reinforcement over one row high)
  • landscape block walls ( expensive and take up more space),
  • natural stone (even more so).
  • If there is a sawmill nearby you can sometimes get slab-wood, the pieces that are sawn off logs to make structural timbers.  These will only last 3-4 years but are very cheap(sometimes free) and can be replaced easily.  Otherwise any untreated 4" or wider salvage wood will create a good boxed base and then you can hill up another 4" of free standing dirt on top of that.

One more thing - whether you do free-standing or boxed beds you need to get your roto-tilling done first.  This week may be the longest dry-spell we have all winter given the El Nino effect.  So as soon as we get a thaw, put your tillers to work.  Soil that is tilled now will break down clumps and turf before Spring.  If you wait until April you will be dodging showers and trying to work new ground - a recipe for a late garden.

Here are a couple of other views on the subject.

Pressure-treated wood: Old poisons, new cautions


Does Pressure-Treated Wood Belong in Your Garden?

http://www.finegardening.com/design/articles/pressure-treated-wood-in-beds.aspx Hope this helps you as you begin to think about your garden this year.


* Since we appropriated the name of Sun's Blog from George Harrison, we thought we'd pay homage with this. From the Concert for Bangladesh: