Lettuce Yellowing And Leaf Spot

The spots are a leaf-spot fungus. This usually isn't fatal to plants and most often happens when foliage is damp for a long time or overnight. If the spots you see are mostly on the plants next to the soil, as in this photo, that's what's going on. Clip them off and only water the plants in the AM, not in the evening. Additionally, all plants grown under lights indoors benefit from a fan placed nearby and set on a timer to go off for a few hours a day. This helps strengthen the plants as well as keep the leaves from staying damp for too long and encouraging leaf spot.

The pale color could be several things. 1. If you're using common gro-lights or fluorescent bulbs they should be only 3 or 4 inches above the plants. If you're using high-intensity bulbs they can be higher. 2. Have you fertilized recently? If not, it could be time to do so as your plants are large enough to need more nutrients. Use fertilizer according to directions on label. 3. Be sure you're not keeping the soil too moist - this will lead to root rot which produces yellow plants. Water deeply less often - let the surface of the soil go dry before watering again...a fan will also help with this.