Valley Permaculture Alliance

My landscaper just put in my first raised garden bed. I'm new to this, but when he said he lines these with tar before filling it up with dirt, I told him to wait. I may want to plant edibles in this bed at some point, and I know I will want to plant edibles in the raised beds he's about to add to the back yard. So, tar does not sound very appealing (or appetizing). Is tar necessary? Is there a natural lining material that is just as tough?

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We have three raised beds which are 36" high, 54" wide and 180" long, they are made of concrete block.  We built them two years ago and I understand your dilemma.  I couldn't find a thing to coat the walls which were acceptable.  We ended up leaving it untreated and have no regrets.

For the beds we're building later in the back yard, I would consider not lining them. However, this is for a bed on the front of our entry courtyard wall, which will be faced with stone. I want to make sure this one stands the test of time.

Dawn, just an additional FYI - since this is supposed to last a long time -- if the bed is more than 18 inches tall you may wish to ask him about 'cross-bracing' - a 3 foot or so tall raised bed, even made out of cinderblocks or bricks can eventually collapse from the weight of the soil and water.  It is generally done in opposing cross angles at 1 foot and again at 2 feet with rebar.

He did this already. Thanks! :)

Great - a lot of folks new to raised beds are not aware of that issue.

Tell him to put cardboard at the bottom and leave the rest untreated. If you water enough, hopefully the worms will come up from the bottom through the cardboard into your beds. With tar, that will never happen.

As Jon indicates, cardboard, and you can also line the sides with cardboard.  Eventually the side soil will firm up by the time the cardboard breaks down forming its own barrier.  Be sure to NOT plant closer than 6 inches to the sides of your raised beds so the soil acts as an insulator.  Also the bed should be at least 18 inches deep for maximum production and health of the plants.

cardboard.

Thanks! I like this idea, and I'm going to research it. Although I am hearing that the tar is an industry standard that may not be as problematic as it sounds, a more natural solution is much more appealing to me.

Thanks! I'm going to research this. I like this idea a lot.

Ugh!  That is just so bad.....might be time for a new landscaper.  Just sayin'....

I have two raised beds made of pine planks and did not line them with anything.  No regrets here either.

What purpose does he feel the tar delivers to the raised bed?  Aside from not allowing anything inside it to breathe?  I guess it would keep weeds from sprouting up through the bottom but as Jon pointed out, neither will worms come in.

These beds are cinderblock, not wood, which is why they need to be lined with something. Also, they don't ever line the bottom, just the sides of the cinderblock (at least that's my understanding). It keeps the water from damaging the cinderblock and keeps the cinderblock from leeching the good stuff out of the soil.

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