All these ideas are good. I agree with Ken that your zinnias don't like their roots disturbed. I start mine in six packs and transplant them as gently as possible without disturbing their roots. If you were pricking them out into a bigger pot, that could well be your trouble. Fortunately, they are easy to start from seed and take off fast once the weather warms. Even if you have to start over, there's still time.

ZG, I see this is your first day here. Welcome to the GardenWeb. White powdery spots are probably Powdery Mildew, perhaps the most common zinnia disease. Prevention is the best cure. Powdery mildew likes to grow in a cool shady dry place. This time of year you can't do much about cool, and the days are getting shorter. Next year, plant your zinnias in those locations that get the most sun. Wet foliage does promote several zinnia diseases, but it's a myth that wet foliage promotes powdery mildew, so don't hesitate to spray your zinnias with something like GreenCure®. In the Fall, frequent sprayings are justified. You can include a photo in your message by using the [img src="URL of photo"] HTML, but use angle brackets instead of the square brackets [ ] that I just used. In order for your photo to have a URL, you need to post it on one of the photo hosting services, like PhotoBucket. For example, if I type, <img src="http://img.photobucket.com/albums/v608/MaineMan/986wides/100_4530.jpg"> The result will appear as, I used a "trick" to keep the angle brackets from taking effect in the example above. There are several other image hosting services, but PhotoBucket is a popular one, and its basic service is free. ZM

overwatering could do it. Brown crispy edges for houseplants are usually overwatering , underwatering or overfertilizing.

Post this one on annuals. There is an explanation but it's escaping me at the moment.