Garden mulch is beneficial to both your garden soil and your plants. Mulch slows the evaporation rate of water out of your soil, reduces weed growth, moderates the soil temperature in both the winter and summer, adds nutrients to the soil and helps prevent soil compaction. Black mulch, due to its dark color, absorbs more of the sun's heat. This allows the garden soil to warm up fast in the spring compared to surrounding soil. Warm soil allows your plants to flourish sooner in the spring and last longer in the fall.
Plant your plants in the garden bed. Space them appropriately, according to their specific instructions, to avoid future crowding.
Calculate the square footage of your garden bed. Multiply the length by the width of the garden bed to calculate the square footage. For beds that are irregularly shaped, estimate the square footage by using approximate measurements.
Calculate how much mulch you need by using an online mulch calculator (see Resources). Enter the square footage of your bed and your desired mulch thickness. It will then output the amount of black mulch you will need in cubic yards.
Pick out a black mulch that retains its color for a long time. Some mulches degrade quickly, so your black mulch could end up gray in a matter of a month or two. Mulches that are labeled "Colorguard" are known to retain their color. Order the amount needed from the calculation in Step 3.
Spread the black mulch in your bed. Rake it smooth until it's at the depth from the above calculation. Keep the mulch a few inches away from your plants to prevent them from rotting.
Add black mulch to your garden bed each year to bring it back to the original depth. This will also refresh the color to keep it rich and black on top.