Problem: Yellowing veins, especially on young, new leaves, or yellow leaves in general. Solution: Yellowing veins may mean your plant needs more iron or magnesium. Give it a trace element fertilizer. If you’re not sure which one to use, take a few sample leaves to your local garden center or nursery and ask for help. Leaves that are turning yellow all over can mean the plant needs fertilizer. Use one formulated for whatever you're growing, such as an orchid or a foliage plant like this Diffenbachia. Follow label directions.