Organic Mulch

• Organic mulch that is smaller in size than 1.5 inches not only suppresses weeds, but also contributes nutrients to the soil depending on the type that you use. Gardeners growing acidic loving plants like roses or azaleas can use a mulch that helps keep the soil within the plant's preferred acidic range, as well as keep weed growth down. Pine needles, pine bark and peat moss are acidic mulches.
  
  Those growing alkaline loving plants like wallflowers can use compost to mulch their beds.
  
  

Inorganic Mulch

• Inorganic mulch is more expensive than organic mulch, but it provides longer weed suppression. Gardeners who use gravel, pebbles, sea glass and sand do not have the problem of the mulch decomposing within one or two growing seasons.
  
  It is important to spread inorganic mulches evenly throughout the garden bed to achieve uniform soil temperatures and soil moisture. While inorganic mulch is able to withstand several seasons, it works best at controlling weeds when a layer of black plastic or landscape fabric is installed underneath, according to the University of California.
  
  

Black Plastic

• Black plastic suppresses weed growth by preventing sunlight and water from reaching the soil. Weed seeds have a difficult time germinating from lack of sun. The black plastic raises the temperature of the soil, which can suffocate existing weeds.
  
  Unfortunately, black plastic isn't effective over a long period of time because it easily tears and restricts the air movement in the flower bed. Lack of air can encourage fungal diseases.
  
  

Landscape Fabric

• Landscape fabric offers gardeners numerous benefits. It allows water to pass through and air to circulate in the beds. Also, landscape fabric can last at least four years in the flower bed, according to the University of California.
  
  To install landscape fabric, cut the landscape fabric to the size of your flower bed. Cut X-shaped holes in the landscape fabric to plant through or pull over your existing plants. Secure the fabric to the ground with landscape pins. You can increase the fabric's weed control abilities by spreading a mulch over the material.