We have cells of parsley, marjoram, and basil that need thinning. This is the hardest part of gardening--willfully destroying plants! How do you thin? I use a pair of tweezers to remove seedlings that are too close together. I'll thin again just before transplanting into 4" pots. Our basil and parsley have been thinned, but the marjoram stems were too small to thin yet with my tweezer method. When do you thin, and at what size of the seedling?