Assuming your plants are getting enough sun, heat, and decent soil, there are a couple diseases that can play havoc with them. See link.

Also, years ago, I had a big bed of them in New Orleans. The neighbor cat liked to urinate in them and they definitely did not like that. It would often kill them.

Hope this helps. They are a great annual.

Here is a link that might be useful: Possible problems with vinca

but there is no disease.. that EATS OFF FLOWERS ...

also.. what tree are you gardening under.. and if its maple.. that is your water problem ...

also.. vinca.. if i am not mistaken.. roots rather easily.. so learn how to do that.. and you wont have to keep buying more plants ... just snip some pieces off the ones that are thriving .. and learn how to make them grow into plants ...

ken

Donna, I looked at your link, thanks. However, I wish they wouldn't call them "annuals". They aren't annuals. I have one that's 2 years old and blooming like crazy. The article also correctly identifies them as perennials. It has nothing to do with freezing. People think tomatoes are annuals, too, but they aren't.

forgive me.. the heat must have got to me..

when speaking of rooting.. and tree competition above.. i was thinking about the perennial vine vinca.. not the annual periwinkle..

as gilda used to say.. never mind...

ken

....and so the confusion continues....lolol! "Annual Vinca" is Catharanthus roseus, and is indeed a herbaceous perennial. And Ken, you CAN take cuttings from this plant, because it IS a true perennial, even though most of us grow it as an annual.

cpski, this is a plant with a well documented history of diseases. I noticed that this problem seemed to get worse as these plants became more and more hybridized, more colorful. It's as if their resistance to problems has become bred out of them....something that we see with lots of ornamental plants (roses would be an example).

If it helps at all, I've always considered this plant to be a good choice for the xeriscape. Once established it requires very little watering. They seem quite susceptible to root rots and leaf/flower diseases if kept too moist. I've referred to Catharanthus as a good parking lot plant...full sun, no irrigation.

yeah.. but dont forget.. here in z5.. rooting annuals.. this late in the season.. means.. it might near flower.. 2 days before first frost.. lol ...

i did periwinkle.. 20 years ago.. i knew there was a reason.. it wasnt worth the annual investment ...

listen. enjoy what survives.. and i will yell...

FIND SOMETHING ELSE FOR NEXT YEAR...

and then. in 20 years.. you can say.. oh yeah.. periwinkle.. i used to grow that .. lol ...

now be honest.. the only reason.. you planted it.. was so you had a reason to say.. periwinkle.. repeatedly.. lol ...

i like the tree.. liquidamber.. cools names rock ...

but i digress...

ken