Tan Spots on Leaves
Q. I'm having problems with tan spots appearing on the leaves of my plants. These are San Marzano tomatoes that I started by seed. I'm using the Gardener's Tomato Success kit as part of my indoor grow experiment. I'm located on the front slope of the Rockies in Colorado @ 8,500' alt. If you aren't familiar with the kit, once you plant, you top water for the first month and then use the reservoir and wicking system thereafter. I'm still within the first month. I have them under a 4 bulb T5 fixture w/ 6,500k bulbs. Humidity is not an issue as it has been 15% or lower here.
A. You didn't mention how close you keep your plants to the lights - but those spots look like an indoor version of sun scald. It could be that the lights are crisping your leaves. Double check to make sure plants are more than 4 inches from the lights!
Good luck and happy gardening!Your friends at Tomato Dirt