Mulch applied to perennials now will help reduce the stress brought on by summer heat. Mulch can help maintain soil temperatures and moisture levels and as well as control weeds and improve the overall look of your garden. There are many different kinds of mulch materials, but only two types, organic and inert. Organic mulch includes shredded cedar mulch and bark chips.
Inert mulch includes weed barrier, rock and gravel. Rock mulch can provide a very uniform appearance. It looks great. It stays in place, won't blow away and it doesn't decompose. Rock mulch is available in a variety of colors, shapes and sizes. You can save yourself some time by applying a pre-emergent, to keep seeds from ever germinating. You should prepare the area by first removing any weed or unwanted plants. You will want to install the rock mulch over a weed barrier, for best results.
Though not as common, weed barrier can be used as mulch by itself. Be sure and choose a fabric weed barrier, which will let moisture move into the soil and allow the soil to breathe. Plastic weed barriers smother the soil and will break down over time. This type of fabric weed barrier is convenient, because it is marked every 12", making planting and landscaping alignment easy. The advantage of laying a weed barrier first, is that you can always add rock or wood mulch later.
One of the most common types of mulch is cedar mulch. Cedar mulch is very advisable for perennial beds, because it maintains its look and consistency for a long time and the color highlights the plants well. It should be applied to a depth of 3" to 4", after the weeds have been removed from the area. Mulch this deep should be sufficient enough to prevent weeds from establishing and help maintain moisture, while adding a uniform and neat appearance to your perennial bed.
Remember, each landscape is different and unique. You may have to use a mixture of mulches in order to achieve the best balance between plants needs and overall looks.