I have read all the articles in DG about lasagna gardening and I'm still not sure about this. I broke down 2 huge heavy cardboard boxes at work to lay the groundwork for a new raised bed we're getting ready to build-12' x 4' x 12" deep.
DH thinks the cardboard is too thick and won't break down fast enough. I said I thought that was the idea, that the bottom layer is supposed to prevent weed seeds from germinating. Who is right?
When I put 1/2" of cardboard in my new raised beds -- AND SOAKED IT -- and put 24" of leaves on top and covered with black plastic all winter, by spring, the cardboard was still there in remnents. And the earthworms were 3 per handful of dirt Water DOES go through it. Earthworms DO eat through it. Weeds have NOT gone through it.
But you have to be a diplomat, so how about putting down cardboard on HALF the bed, try it through a season and see what works for your yard and your gardening methods.
Cardboard will get watersoaked pretty quick. 12 inches of dirt by itself will block germinating seeds but not things like grass clumps and wild garlic that can sprout up through. Those get blocked by cardboard or paper fiber, keeping them from going right on up and getting to the sunlight.
DO use the cardboard and/or a thick layer of b&w newsprint. I do it for all my raised beds. It's SOP for me - never turned over any of the native soil, either. Within 2 years I could sink my hands almost elbow deep into the beds - no weeds/grass erupting through the barrier, either.
Thanks again everyone!! Well, it's done. DH & I worked all day Saturday (well at least I worked all day :)) and the bottom of our bed is cardboard. Then wood chips, newspapers, lots of compost, straw and shredded paper from work. It's almost full and I am tired, tired, tired. Had to come back to work to rest!!