How to Create a Lasagna Garden
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Step 4: Make Subsequent Layers
Alternate the brown layers with layers of greens. A lasagna garden can have as few or as many layers as you want. Like a compost pile, it can be quite large as long as the material in the layers can still get some air. Don’t add more greens than browns or your bed will heat up too quickly, becoming acidic and potentially creating more carbon dioxide than the soil can handle. Green ingredients can be harder to find than browns. If you save your kitchen scraps, this is a great way to use them, though most people don’t have a large enough quantity to make a big addition all at once. Grass clippings, coffee grounds and herbivorous manures are other good alternatives that may be easier to obtain. If you’re collecting lawn clippings from a neighbor, make sure no pesticides or herbicides have been used on the lawn.
With manures, fresher stuff provides more nitrogen than composted manure. Poultry manure tends to be hotter (more nitrogen-rich) than cow or horse manures. Also be aware that any “manure” you obtain actually may contain a lot of straw, sawdust or other bedding material, essentially rendering the final product more brown than green.
Pea and bean vines, alfalfa hay, weeds (without seed heads), and scavenged seaweed (rinsed to prevent salt buildup) are other possibilities that contain some nitrogen. If you run out of green ingredients and cannot obtain what you need locally, visit a nursery and spend a few dollars on some seed meal or balanced organic fertilizer; a thin sprinkling of either one will greatly boost the nitrogen levels in your bed.
Other things you can put in your layered bed include soil, which some gardeners add to their compost piles, as well. This may moderate the biological activity and slow things down, but it can encourage more earthworms to take up residence, and this always improves decomposition and soil building and guarantees that the soil layers get mixed well over time, including the subsoil. Although some gardeners have success growing in pure compost, adding some soil will ensure that the final product is well mixed and has some of the sand, clay and mineral components of soil in addition to the organic matter.
You can add other minerals to your bed at any point. Some gardeners add bone meal or fish bone meal for phosphorus and calcium, greensand or kelp meal for potash and trace minerals, or rock dust for trace minerals.
Step 5: Let the Garden Cook
While you could mix your layers together by turning them like a compost pile as they decompose, they’ll break down just fine when left alone. In his book Weedless Gardening (Workman Publishing Company, 2001), Lee Reich states that leaving mulch layers in place also helps the soil absorb the proper amount of water, which tends to run off the surface when too much soil is exposed.
Once you’re finished, cover the lasagna garden with soil or with one final layer of browns, such as straw or leaves. Keep your bed moist, and water it as needed. If digging animals are a problem or if you want to heat things up more quickly, cover the bed with a plastic tarp that’s weighted down on the sides or secured with ground stakes.
Some people plant in lasagna gardens right away, and the plants will grow just fine in the decomposing mulch. But the ones you plant next year will be the real stars, because by then your soil should be just right.
This article originally appeared in the May/June 2011 issue of Urban Farm.
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