Setting: I have a summer-only outdoor herb garden on a 9th story, S-SW apartment patio. I live in Canada Zone 7a/7b/8a (the boundary is really fuzzy here; general PNW perpetual overcast).

Problem: My oregano was covered in tiny, oblong white eggs. I ignored them (sigh), and they hatched into bright green inchworms. By then, the entire garden was infested. Luckily, it was the "How did you even survive the winter?!" collection of almost-dead herbs, so I removed all plants, cleaned all containers, and restarted with all-new dirt. I scrubbed the entire very-tiny concrete patio: the eggs & insects should have been gone.

I restarted my garden, and less than a month later, my (new) greek oregano and the neighbouring lime mint are coated in tiny, oblong white eggs. I've removed the infested plants, but does anyone have suggestions on how to prevent reoccurring infestations? Is oregano particularly susceptible, or just unlucky?