Most soil is a mixture of organic matter and ground rock which contains a variety of nutrients. Mulch is a material which is used to cover the soil to prevent weed growth, cool the soil, hold in moisture, or just to provide a certain appearance to the landscape. Mulches include chipped bark, gravel, landscape fabric, shredded leaves, pine needles, recycled rubber, newspaper, etc.Soil and compost are also used as mulches when placed on top of the ground.
If you want to improve your garden soil or add nutrients I would recommend adding compost - either as a mulch or mixed in. If you want to cool the soil, hold in water, suppress weeds, or give your garden a certain look then I would recommend a mulch. The type of mulch you use is up to you.
I would not use recycle rubber because unless you put down a heavy duty landscape fabric first it will mix in with your soil and will be very difficult to remove. Rubber also can contain toxins - both from the rubber itself and from the tires it is usually made from since tires pick up oils and other things from the road. Gravel mulches will warm the soil but may warm it too much.
Gravel would also be difficult to remove. Paper, leaves, pine needles and similar products will break down over time and feed your soil.
Your main concern when organic gardening is soil health. You want your little ecosystem to be as strong and healthy as possible to support the plants you're growing and the beneficial microorganisms within the soil that depend upon your plant's byproducts for nourishment. As you know, these elements work symbiotically to create the best environment for all to survive.
Most gardeners begin with a test kit that will provide a detailed analysis of the nutrients present, as well as the acidic or alkaline reading and the drainage level. More on Organic Gardening - perennial-gardens.com/flower-articles/or....
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