Stem thickness indicates the age of the plant (and not the age of the stalk), with the thicker stems coming from older plants. Older, thicker stalks can be woody, although peeling the skin at the base removes the tough layer. Peeled asparagus will poach much faster. The bottom portion of asparagus often contains sand and soil, so thorough cleaning is generally advised before cooking. Plants bearing seeds produce spears that are smaller and thinner, and plants without seeds produce larger and thicker spears. Thickness and thinness are not an indication of tenderness or toughness. The stalks are thick or thin from the moment they sprout from the ground.