California Landscape Contractors Association
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North Coast Builders Exchange
We have included some resources here to help with your garden planning.
Adding mulch in your garden is one of the simplest ways to beautify your yard. A layer of mulch 3 to 4 inches deep will keep most weed seeds in the soil from sprouting and increase moisture retention. Around shallow-rooted plants limit the depth to 5 to 6 inches. Remember to pull back mulch from the base of plants so it doesn't cause rot. Many materials, like wood chips, settle so add an extra 1/2 to 1 inch of the material to account for the decrease in volume.
If you want to use organic mulch on slopes apply a shredded type about 6 inches deep; it'll mat together and stay in place better than a thinner layer.
To add soil amendments to unplanted clay or sandy soil we recommend spreading 4 to 5 inches of amendment over your soil. Spread the material evenly over the soil and then work it in by hand or with a rototiller to a depth of about 9 inches. This will give you a planting area that is approximately half soil and half amendment. If the soil is loamy or has been regularly amended each season just add 2 to 3 inch layer of amendment; you'll have a top 9 inch layer of about three-quarters original soil, one-quarter amendment.
Don't use fabric under organic mulches. It's better to let them decompose and mix into the soil.
Here is a mulch calculator if you are unsure about how much mulch or amendment you will need.