After putting in the structure of my cedar raised garden bed, I have been gradually filling it with layers of compostable material along with the soil I had taken out. This is called “sheet mulching” or “lasagna gardening” and is a great easy method to enrich the soil. In its most complete form, sheet mulching includes laying down cardboard or newspapers on top of whatever is growing on the ground (lawn, etc.) without any digging required. But since I wanted to have a deeper root zone in this raised bed, I did weed the soil and dig down deeper. Autumn is an excellent time to sheet mulch because the bed will have all winter to decompose and be ready for planting in the spring.
This is a form of composting in place, so you alternate layers using amendments rich in nitrogen (called “green”) or carbon (“brown”), but it also depends on what you happen to have in your yard. A basic permaculture principle is that waste is just nourishment for another part of the life cycle. So we are taking “waste” and giving it a chance to grow food next year. We have lots of leaves in our yard, so that is an important source of “brown”, and we also live within a half hour of the beach, so we use seaweed gathered at the shore as a source of “green.” I had a chance to go to Kettle Cove on Sunday to gather a bunch.
Here is my list of layers from the bottom (5 inches below ground level) up, with some photos along the way:
- soil from the site
- rock dust: I added some handfuls of rock dust, which adds trace minerals (I had collected a bucket-full a few years ago from a local quarry.)
- a bit of old seaweed, collected earlier this year.
- leaves mixed with a little bit of grass clippings, from Margy’s leaf collecting.
- a few branches (I remembered this from my hugelkultur adventures) These are good for water retention, slow release of nutrients—I just added a few, and then buried them in the leaves—I could have done a lot more, but also didn’t want to limit the roots.
- more soil
- After my trip to the beach, I added more fresh seaweed, a generous layer of it: seaweed is a great source for nitrogen, potassium, phosphate and magnesium, and many trace minerals. Note, I also added the second layer of cedar planks to bring it to its full height of 11 inches.
- more dried leaves with a little bit of grass clippings
- composted coffee chaff (which was in a barrel we kept next to our compost bin to add after kitchen scraps: after a couple years it composted itself!)
- more soil
- a couple inches of composted manure: we have a pile of it from last year, but we have to sift it because it has become full of roots.
- green cuttings from garden cleanup.
- leaf mould from leaves left in a barrel for a couple years
- more leaves to top it off.
And today it is complete! The rest will be done by winter, and soil creatures and time.