The young plants are in a cold frame waiting for the last frosts. The leaves have dry white edges and is spread over all of the plants.
My Young Lobelia Plants Have White Edges to the Leaves. How Do I Cure?
Certified GKH Gardening Expert
How much sun are they getting in the cold frame? Most likely this is sunscald, which is like sunburn in plants. This typically happens to plants that are not acclimated, but can happen to new growth on plants that are in locations that are a bit too sunny for them. If possible, move the plants to a location that is not quite so intense or you can try to shade the area some by placing a large umbrella (or something similar) over it.