Leaves are a good material for mulch. Shredded leaves can help control weeds from sprouting in your garden. You can use leaves from any deciduous tree. Oak leaves can be used as well because contrary to popular belief, these leaves will not acidify the soil since they lose their acidity as they decompose.
Spread the leaves 2 inches deep, shred or chop them before spreading. Whole leaves are easily blown by the wind.
Avoid mulching with wet leaves when the climate is cold. Cold climate can freeze wet leaves.
Soil under mulch is also rich in helpful organisms like earthworms. Try digging into your mulched soil and you will see a lot of earthworms, these earthworms will turn your mulch into the best fertilizer for you plants.
Pine needles decompose slowly and water can seep through your mulch easily. They will not change the pH of your soil even if you make a 2 or 3 inches of mulch. The good thing about pine needles is that they smell good and they become attractive as they decompose.
Grass clippings are great for your vegetable garden; you can find grass clippings anywhere in your garden. Do not use grass that has been treated with herbicide though. Grass clippings decompose quickly; and they decompose more quickly on very hot weather. Make sure that the grass clippings are dry when you spread them in your mulch. Spread grass clippings 2 inches deep and reapply often. If you applied it too thick, they will mat down and they will become impervious to water.
Plastic is the best material for your mulch if you are growing warm weather crops in a cool weather. Plastic helps in heating up the soil when the weather is cold and you can also avoid weeds from sprouting in your garden.
Clear plastics warm the soil quickly but they allow weeds from growing. Black plastic prevents weed-seeds from germinating as it warms the soil.
The disadvantages of using plastic as mulch is that they cost high, require a lot of efforts in piling and removing, they end up in the trash after the season, and they divert water out of the garden beds.
Straw does not mat like grass and leaves so you have to make a pile of 6 to 8 inches deep. The good thing is that straw breaks down quickly and they add nutrients to the soil. Do not use straw mulch during rainy season, wet straw will rot and they will become a hideout for slugs. Make sure that you buy a straw and not hay. Hay can encourage weeds from sprouting in your garden.