Of all the different kinds of mulch available, hardwood bark mulch seems to be the most popular, undoubtedly due to its low cost. It is the least expensive mulch found in the Heartland. Every sawmill in the Heartland produces hardwood bark mulch as a bi-product of the milling operation. Because it is so plentiful and local, hardwood buck mulch seems to be the mulch of choice.
There are some drawbacks to hardwood bark mulch. Pest control companies say that this mulch attracts termites. I doubt that it attracts termites, but there is no natural termite repellent in hardwood bark mulch. If termites are in the area, they will certainly like the addition to their home range.
Hardwood bark mulch tends to deteriorate rapidly and often forms an impervious layer on the surface of the mulch bed. This impervious layer often contributes to the demise of azaleas and rhododendrons.
Cedar and cypress mulches are also available in the Heartland. Both of these woods have natural insect repellents present. In addition, these mulches do not break down as rapidly as hardwood bark mulch.
Many gardeners like to use pine bark mulch, pine mini nuggets, or pine nuggets. The mulch is similar in appearance of hardwood bark mulch, but it does not form an impervious layer, as does hardwood bark mulch. The nuggets and mini nuggets are just larger particles of bark, great for use around azaleas and rhododendrons. Unfortunately, the nuggets and mini nuggets blow in the wind and can be moved easily during a heavy rainstorm.
More and more azaleas and rhododendron growers are using pine needles as mulch. In southeastern United States, pine needles as used quite extensively, probably due to their abundance and low cost. In addition, leachates from pine needles keep the pH of the soil close to 5.0. Low pH is just what azaleas like.
If you want to have the sweetest landscape in town, try using cocoa bean mulch. This mulch is derived from the husks of cocoa beans. Its small particle size gives your landscape mulch a more formal look. It usually stays where you placed it no matter what the weather. Its only drawback seems to have cost.