Someone asked me when Vinca should be started, I had 12 weeks, which seems early, their packet has 6 to 8 (both for CATHARANTHUS roseus) .
One site actually says they are slow to take off outside, so that may be the reason for the varying dates, depending on how big you want them when you transplant... here are the references I've found. Can anyone clarify, or is it just trial and error :)
Start early. I started mine Feb 17 last year, and they were still relatively small when I began planting outside. I like to start transplanting around Mothers' Day. I have to say also that I was disappointed with my plants last year. I think that I got the seeds either from Stokes Seeds or Thompson and Morgan. Those that grew did beautifully, but my overall germination rate was low.
Once they started blooming, they went like gangbusters, but it seemed to take forever for them to be sizeable.
Vincas like to have a rest period. They come up and will liek sit and sit and sit for months, then all of sudden when the daylight is long enough and the temps high enough then they will kick in.
Last year I had Vinca plants that got up to 4' tall and as wide and bloomed all the way until january when a real hard killing frost took em out.
Vinca is kinda tough to get started, but once it does and gets established it very drought tolerant.
Actually, vinca germinate sbetter when you have older seed . If you using freshly harvested seed, best to wait 4 to 6 months before sowing it. It needs a period of dormancy rest inside the seed.
You want to cover the seed, place in total darkness and start germination temps at 80 F. Most seed will germinate in 6 to nien days. Once you have emregence then you want to brign into the light and drop temps down to about 75F no lower.
It takes about 14 to 15 weeks to get the seedlings to a 6 pack size and 16 to 18 weeks to get to a 4" to size .
The big thing to rememebr with Vinca is it doesn't like cold anythign lower than 65F at night and you get stuntd and leaf diseases on yoru seedlings.
They take a bit of work, but once ya get the hang of them they really a beautiful plant that will survive in alot of areas where other plants won't.