Heirloom Herb. Catnip seeds won’t produce a plant that would win a beauty pageant, the greyish-green, heart-shaped leaves make a soothing tea. And of course cats go wild for it! In the garden plants can grow to 90 cm (3′) high. Catnip will self-sow and establish persistent stands. In most situations, catnip is a short lived perennial hardy in Zones 3-9.