Because they're made from trees, hemlock and cedar are both organic mulches. Both make good choices for gardens because they will break down eventually, adding nutrients to the soil and improving plant growth. When applied correctly, both types of mulch can stifle weed growth. Cedar and hemlock mulches have some key differences, too.

Mulch
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A wheelbarrow of mulch in the backyard.

Pros of Hemlock Mulch

The primary appeal of hemlock mulch is that it's attractive -- hemlock has a rich, reddish-brown color that lasts. It is sometimes dyed -- so if you pick it up and it stains your hands, you will know the color is "enhanced." It also has a distinctive fragrance that is said to deter bugs.

Cons of Hemlock Mulch

Hemlock mulch is highly acidic, which means you should only use it around plants that can tolerate acidic soil. This makes it a good choice for acid-loving plants. Hemlock is a hardwood, which tends to be fibrous. When shredded, the pieces can weave together and interlock, forming a barrier that inhibits some water from reaching the soil's surface. Chips might be a better bet.

Pros of Cedar Mulch

Cedar, like hemlock, has a distinctive fragrance that is said to repel certain insects. The mulch varies in color depending on where it was harvested, and like hemlock, it can be dyed. The primary attraction of cedar is that it lasts longer than other types of organic mulches -- about two years -- so you don't have to replace it as often.

Cons of Hemlock Mulch

Like hemlock, cedar is fibrous, so it can prevent water from penetrating the soil. This can be a problem in dry climates. In addition, the slow rate of decay -- over a period of about two years -- means nutrients are added more slowly to the soil than with other types of organic mulches. Cedar mulch also loses its color rather rapidly, turning from a rich, reddish-brown to a dull gray.