mulch (n.)

"strawy dung, loose earth, leaves, etc., spread on the ground to protect shoots or newly planted shrubs," 1650s, probably a noun use of Middle English molsh (adj.) "soft, moist" (mid-15c.), from Old English melsc, milisc "mellow, sweet," from Proto-Germanic *mil-sk- (source also of Dutch mals "soft, ripe," Old High German molawen "to become soft," German mollig "soft"), from PIE root *mel- (1) "soft."

"to cover with mulch," 1748 (implied in mulched), from mulch (n.). Related: Mulching.