The larger fully composted bark pieces conserve moisture and improve aeration to the roots. Like a good mulch, SEA SOIL definitely improves the health and fertility of your existing soil as well as the plants in the soil. SEA SOIL is made from 50% fish, which is natures best and safest time release fertilizer. Unlike most mulches, SEA SOIL is already weed free -- so by adding it to your garden you are not only keeping the weeds down but also not introducing new weeds. However, I think one of the most important features in any mulch application is its visual appeal. SEA SOIL has a dark rich color and it makes any plant bed look clean and beautiful.