Black mulch is dyed with carbon black. Carbon black is pure elemental carbon and is used in many commercial and industrial products. It is considered non-toxic and has no known adverse effects.
Mulch is spread over soil to retain moisture, prevent weeds and keep the soil cool. It may also improve the appearance of the garden bed. Organic mulches aid in fertilization as they decompose. Bark mulch is commonly used around trees and shrubs. Newspaper mulch can be used to smother weeds. Straw and hay are often used as mulch in vegetable gardens to make the paths less muddy and to keep soil borne diseases from splashing up on a plant's lower leaves.