Transplant veggie starts when they have four true leaves. The first two leaves that emerge from a seed after it germinates are called cotyledons. They are special and wonderfully encouraging to see but don’t count them. The true leaves will have a similar leaf edge and leaf shape to the mature plant. If you are not sure what you are looking for google the plant you are trying to grow or take a look at the seed packet. Four true leaves is the magic number because that usually means that the roots are well enough developed that they will hold onto some dirt during transplantation. But, the plants are not old enough that they they have been tremendously stunted by starting in pots. Remember these volunteer starts (link to ‘squash transplants’) now, as you can see from the photo above, they are happy out of their pots.