New to SFG Need Advice, Contaminated ground soil

Hello
We have decided to SFG. We decided to do this due to the fact that two years ago we discovered old contaminated soil on our property. The short of the story is, the soil smelled heavily of old fuel when we
were excavating for a new septic system. We went through the whole
testing of the soil as required by law in Massachusetts. The contamination was old gasoline and kerosene. the soil and ground water has been tested and we were told it was safe. Even though were were told it was safe, we do not want to plant edible plants in the soil. For years we attempted to grow garden vegetables before we gave up. We figured it was something we were doing wrong. The plants never thrived nor did they produce vegetables larger than 2" in length or girth. We now believe it was the soil all along.

Thus we decided to start a raised bed garden. While researching raised bed gardening we stumbled across this website. We then bought the All new square foot gardening book. We like what we read and have begun building two 4x4 beds.

Our question is this. Prior to finding the SFG method, we had planned on building 4x4 boxes 12" deep and lining them with plastic to ensure that our plants roots would not tap into the contaminated soil. But after reading the book we question whether we really need to make them 12" deep. Will the plants roots grow through the bottom/weed cloth? We assume no.

Second question would be. Can we use plastic for the bottom rather than the weed cloth? We have both at our disposal.

Thank you for any advise offered,
Lisa and Jim in Mass

If you're concerned about your plant roots coming in contact with the contaminated soil having a plastic lining would ease your worries. If you REALLY didn't want to worry, you could put a plywood bottom on your boxes. I did this on one of mine this year. You can see the video of it here: http://www.timsbackyard.com/2010/03/building-basic-square-foot-garden.html

6" is deep enough for your plant's roots, but if you plan to plant long carrots or potatoes you will want the extra depth. You might consider one box 6" deep and the other 12" deep. Or make them both 12" so you can rotate crops next year.

All my SFG beds are table tops, weed cloth on top of welded wire screen. I've never had roots grow out the bottom. Plastic would work but it needs holes punched in it for drainage.

All my beds have been 6 inch except for my carrot/parsnip box which is 12.

If I were only going to grow a couple squares of carrots or potatoes, I would do the portable high-rise box that Mel suggests: a four sided box that sits on the soil of the box to give the extra depth one wants. There are carrot varieties that don't need more than 6 inches of soil.

Thanks for the replies and advise. We feel a bit better now that someone else has given us some input. The plywood bottoms will certainly put our minds as ease.

As for root vegetables. We had read that we could make a smaller version of boxes 12" deep to grow in. I think that is what we will do. As we will have enough lumber left over. We purchased enough lumber two build 2 12" deep boxes. Thus I think we can actually can build a box for turnips and another 4x4 box.

Thanks again guys,
Lisa & Jim

Welcome, fellow Massachusetts-ites!

I am not happy about the cause of you finding us, but I bet you will end up being very happy you found us!

And I would absolutely guess that the soil was the cause of the problems you had previous years.

Martha
Thanks for the warm welcome. You can imagine how unhappy I was to find the contaminated soil. Not only did I grow up next door. I cherish our little neck of wetlands, woods and wildlife.

I am very excited to once again have a vegetable garden. We have lots of perennial beds. They seem to do fine, as they are not in the central area of our backyard.

Lisa

I think the weed barrier must be permeable both ways - it lets rain water out and I bet it lets water (oil) back in. I think I would put down plastic (with a few holes for drainage) and then a layer of sand or gravel. But maybe I'm over cautious.