My coreopsis in the front started curling last year so I removed all of the curled stems, but this year the new growth is starting to do the same thing. My tall phlox in the back of the house has started curling too. The stem and then the leaves of the phlox as well as the coreopsis in the front are doing the same curling. Should I remove my whole bed of phlox? They are mixed in with my white bleeding hearts. I am very concerned about losing my other flowers.
Here are a couple of possibilities.
First, it could be phytotoxicity, i.e. herbicide damage. If you have been using weed killers/herbicides in the vicinity of those flowers, that can cause leaf curling. Some herbicides with 2,4D will even waft over on a breeze from quite a distance, so it's possible that you didn't use herbicide but someone else did. Here's some information from our website: http://extension.umd.edu/growit/herbicide-damage-vegetables
Second, aphids can cause leaf curling. Look for these insects. Often their coloring matches the leaves and it not readily noticeable.
Here's our website fact sheet that gives a diagnostic chart of symptoms. Scroll down to the curling/leaf distortion entry: http://extension.umd.edu/learn/ipm-series-annuals-and-perennials-hg94
You'll see that there are other possibilities.
If you're still not sure what is happening, send us a digital photo attached to a reply and we'll take a look at it.