Beginner Gardening: Zinnia leaves turning brown and crispy! Help!, 1 by MTGardenGirl

MTGardenGirl wrote:
I'm new to Zinnia and planted some small plants in a well drained, commercial "garden soil" along a fence that gets about 8 hours of direct sunlight a day. When I first planted them, I had a big problem with wilting- I was underwatering due to our notoriously bad weather-man :-) but once I started watering every morning they perked up and rooted. I had huge blooms about 2 weeks ago, deadheaded and am now seeing more buds appearing. The problem is that A LOT of my plants are getting brown and crispy lower leaves. I thought that it was sunburn at first, but I would think that if that were the case, all of the leaves would appear "crispy". Could it be a nutritional deficiency? If so, should I add fertilizer and what type? Could it be an insect problem? My yard has become a haven for ants lately- could they be disrupting the roots? Thanks!