The major reason gardeners use mulch is to snuff out weed seeds by shading them. This allows the roots of desirable plants to access soil, water, and nutrients without undue competition. Mulches free of viable weed seeds—such as leaves, good compost, and wood chips—are best. Weed seedlings that sprout in any organic mulch are easily done in if you periodically fluff up and flip over the mulch with a pitchfork. The second reason to mulch your garden is to conserve water. Organic mulches soften the impact of raindrops so that water can effectively permeate the soil, and all mulches, organic or otherwise, limit evaporation of soil moisture. Keep reading the tutorial in the source.