Minecraft wiki entry for Flower, associated text: When not in peaceful difficulty, wither roses inflict the Wither status effect to any players or non-immune mobs touching it, dealing 1 damage every half second‌[Java Edition only] or two seconds.‌[Bedrock Edition only] The effect lingers for 1 second after the player/mob leaves its block space. Wither skeletons, the wither, and the ender dragon are not affected due to their Wither immunity.