The Most Important Four Inches in Your Garden

By Cam Mather

I delivered one of my books to a friend in town recently. She had borrowed “The All You Can Eat Gardening Handbook” from the library but had decided that she wanted her own copy when she realized that she’d be referring to it throughout the gardening season. She asked me about getting her garden started this year. She had removed the grass and was now trying to get the garden ready to plant. She was hesitant to rent a rototiller because she was afraid she might break it on some rocks, and I don’t blame her. We live in “Stone Mills Township” and the one thing that we grow well in our gardens and our fields is stones. And every year the frost heaves a few new ones up and I manage to hit them with my rototiller. Luckily I’ve never broken it on a rock.

I asked her what she had done with the layer of sod she had removed and she pointed to a low spot where she had used it for fill. I suggested that it would be a good idea to retrieve that sod and put it in the compost heap. Or just pile it up with the grass facing down and cover it with old hay to kill the grass but keep the topsoil. Topsoil is really, really precious, especially in a place like this. When the glaciers retreated eons ago they left very sandy soil with lots of “big” grains of sand (i.e. stones. Part of my garden looks a bit like a small gravel pit.

I can’t remember the exact figure but I think I’ve read that it takes something ridiculous like 50 years to build up an inch of good topsoil. So if you had trees and they dropped their leaves every year and these rotted and earthworms chewed them up and pulled them into the soil, it would take a long time to make a significant amount of soil. So when you remove that top 2 or three inches of topsoil along with the grass, you’re removing the most valuable component of your new garden. When I lived in the city there were a few days each year when yard waste was picked up with the garbage. Some people would leave big piles of perfectly good sod at the end of their driveways to be picked up. People in the city have the money to head over to the big box store to load up on bags of topsoil to replace the topsoil they’ve thrown out. I don’t.

So save your topsoil at all costs. In my book I talk about why I am such a big fan of using rotten hay to expand my gardens. If I put it on thick enough it will kill the grass. I have to leave it a full season for it to work its magic, but I can usually anticipate where my next garden is going to go and so I can invest a full season in killing the grass. Hay is great because it allows water to trickle down through. And it decomposes, so when I’m ready to till it in the following season, not only have I killed the grass, but also I’ve added significant organic matter to my soil. I like to think of hay as “bio-mass”. Some farmer had a big field and this grass grew tall in some previous summer’s sun. It used photosynthesis to make all this wonderful grassy, woody biomass. And since an animal didn’t eat it, I’m now going to incorporate that stored sunshine energy into my soil. I absolutely love it.

The other reason I love using rotten hay is because it doesn’t disturb all that life in the topsoil that I want to maintain. All those wonderful microbes and microscopic little creatures that help organic matter to decompose, or help to free up trapped nutrients and minerals that might be locked in some of that organic matter, so it’s available for the new crop to absorb and pass along into this year’s fruit (or vegetable). This is really important. Again I can’t remember the exact statistics, but some biologists have suggested that there’s more life by weight in the top couple of inches of topsoil, than in all the living creatures that live on top of the soil … humans, cows, elephants, NFL linemen, etc. So when you dig up that topsoil and get rid of it, you’ve lost all those wonderful microbes that your plants need.

If you want a garden fast and want to preserve your topsoil you can just dig up the sod and turn it over. The problem with this method is that it usually doesn’t kill the grass, which will just turn around, and start growing back towards to the sun.

Instead you might want to try “double digging.” Put on your work boots and sharpen your shovel and cut the sod in the area where you want the garden to be into 12” inch squares, like a checkerboard.

Take the first row of sod that you remove and place it about a foot from where you dug it. Then dig out the soil from where the sod was and place it right beside the row. You’re basically digging a shallow trench where that first row of sod was.

Now when you remove the second row of sod, turn it over grass side down into the trench you just dug beside it. Once the row is complete dig another trench where the sod was and pile that soil on top of the upside-down sod.

By doing this you’re making sure that the grass and its roots are buried under a deep enough layer of soil that light will not get down and allow them to live. If you dig the trench deep enough and pile a deep enough layer of soil on top of it you’ll be able to grow a garden on top and not have to worry about the sod.

Plus you’ve saved that topsoil even though it’s a little bit lower than it would otherwise be. If you have healthy soil, earthworms will help circulate that topsoil back up higher, as will the action of the frost and other natural processes. I would wait for a year before I used my rototiller or dug deeply with a shovel to turn the soil over. Make sure the grass is really dead before you risk bringing it back into the grow zone by accident.

With this process I’d recommend a very deep layer of compost or composted manure on top because by digging down fairly deep in the trench you haven’t brought the best soil to the surface. In time these layers will all get mixed up and you’ll have a wonderful, thick, rich upper layer, but for now supplement it and make it deep. It wouldn’t be a bad idea to mulch with leaves or rotten hay to ensure that no light gets through to that lower layer of grass so you’re sure it’s dead by next season.

Topsoil is precious and you shouldn’t waste it. And if you see your neighbor with boxes of it out at the curb on garbage day, fire up your wheelbarrow and get scrounging! There’s gold in those boxes!

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2 Responses to “The Most Important Four Inches in Your Garden”

  • StaceyG:

    Between last fall and this spring, we double dug about 180 square feet worth of garden (between that and the hand-crank grain mill, I’d say I’m getting some good workouts in). For the beds dug last fall, I put leaves on top, raked them off this spring, leaving beautiful dirt to plant in. Though the method is a bit labor-intensive, it’s worth it!

  • CJ:

    I read an interesting tidbit the other day, the old homesteaders used to use upside pieces of sod to start seeds in that they knew would not transplant well. When the seedling was big enough, they put the whole thing down into the garden soil.

    I’m going to do a couple tests this year and if things work out, I’ll have many new seedlings to offer in roadside seedling business next year.

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Cam Mather and his wife Michelle live independently off the electricity grid using the sun and wind to power their home and their CSA. Cam is working towards the goal of making his home “zero-carbon” and with his extensive garden he aims to grow as much of his own food as possible. He is available to speak at conferences and other events and has motivated many people to integrate renewable energy into their lives, reduce their footprint on the planet and get started on the path to personal food, fuel and financial independence.
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