Mulching Materials

• Mulches can be made from biodegradable materials, such as shredded leaves, chunks of bark, cow manure, cardboard or newspaper -- or long-lasting inorganic materials, such as gravel, plastic sheeting, aluminum foil or even pieces of old rubber tires. Inorganic materials only need to be applied once because they do not decompose. Organic mulches, on the other hand, break down over time; consequently, they need to be reapplied each year. The best time to renew mulches is in mid spring after the ground has warmed, but before the annual spring growth spurt.
  
  

Spring Mulching

• To hinder the growth of weeds and help the soil retain moisture, apply mulch in the early spring, about two weeks after the final frost. Mulching materials slow the rate at which the soil warms; applying it sooner will keep the ground cool and may hinder seed germination, which can reduce the overall productivity of the garden.
  
  

Fall Mulching

• To insulate plant roots and protect them from the damaging effects of winter weather, apply mulch in the fall, before the first frost. In the winter, the ground freezes and thaws rapidly. This can cause plants to "heave" or pop out of the soil. Mulching materials blanket the roots, reducing the impact of seasonal temperature fluctuations.
  
  

Application

• There are absolute rules regarding the correct application time for mulch as it can technically be applied whenever it is convenient to do so. While the same can be said for the amount of mulch to apply to a given plant, a 2- to 4-inch layer is generally sufficient. Robust weeds can grow through thinner layers and thicker layers restrict the flow of oxygen to the roots. The most effective thickness does vary somewhat according to the density of the mulching materials. For example, lightweight materials, such as shredded bark or straw, should be spread more thickly than dense materials, such as old carpet or gravel.