Catnip Nepeta cataria
$4 per plant in 9 cm pot
Relax the children, calm your mind, get your cat high. It’s catnip!
A perennial native to Europe, catnip likes to grow in sun or partial shade with moist rich soil. Put sticks around the plant if you don’t want it squashed by yours or neighbouring cats lolling around on it. (I haven’t caught it yet but there must be a white long haired cat around these here parts, judging from the circle of cat hair around my plant. Plant bounces back remarkably well!)