Growing Shasta daisies
Although you mentioned that the seedlings are growing in a well lit greenhouse, they appear to be leggy and stretching to reach light. A more intense and direct light source is needed to improve growing conditions. Maintain a temperature of about 70 degrees. If you provide a cool supplemental light, place it two or three inches above the seedlings and allow 16 hours daily and eight hours of darkness.
Keep the growing medium moist but never wet. Too much moisture allows fungal pathogens to weaken or destroy stems just above the soil--a condition called "damping off."