I bought some organic catnip seeds at the San Francisco Botanical Garden. I prefer regular seeds to the starter kits I normally find in Europe, so this bag was exactly what I was looking for. The weather has been extremely hot during the past month, so my catnip is already quite tall and fragrant, despite the half-sun position. I hope it will survive the sudden cold that is supposed to hit next weekend. Instructions said to sow as late as two months before first fall frost.
The cat seems to like this catnip as much as he likes parsley and flowers, that is to say he likes it a lot, but no weird behaviours so far.