Helichrysum ruderale is a biennial aromatic herb, growing up to 1 m tall, with a stout stem up to 10 mm thick at the base. The stem is unbranched (simple) below the flower cluster, glandular-hairy, and thinly covered in white wool on the upper parts and on the flowering branches. The plant is leafy throughout. Basal leaves are absent during flowering. Stem leaves are up to 180 × 65 mm, decreasing in size higher up. They are elliptic to lance-shaped, with an acute or pointed tip and a broad, clasping base. The uppermost leaves are long- or short-winged and glandular-hairy on both sides, with margins often edged with white wool. Flower heads are mixed (heterogamous), rounded, and 25–32 mm wide, surrounded by radiating bracts and glossy bright yellow. They form large clusters (corymbose panicles) with ascending branches. Flowering is in spring to early summer, between September and November.