I wanted to use artist purple flossflower, or ageratum. Around here,
all I can find is "artist blue", however. (from proven winners) In the
end, I decided to simply start a bunch of purple zinnias from seed, in
several of those jiffy 7 tiny seed starters that has a clear plastic
cover and a dozen tiny peat pots.

I also got a couple of seed packs of purple morning glory. I
remember those being easy to care for, so I'll just direct seed them
along the fence, then mulch them after they come up.