Ever wonder when a seed is ready for storage? One way to tell is by the appearance. Take a look at these nasturtium seeds.
Notice how they are all different colors? The green ones are fresh off the plant, and need to dry for a while. The light brown ones are drying and shrinking, the really dark are closest to finished. Here is another picture to see them side by side. Notice the size of the fresh seed versus the dry storage-ready seed.
See how different they are? There are plenty of seeds that transform this much in the drying process in both color and size. Really fresh looking seeds often aren't finished developing yet, but in the case of the nasturtium, the green seed is done getting its nutrition from the mother plant but hasn't finished drying yet. I know this because they fall off the plant in this state. A seed that isn't finished developing will still be attached to the parent plant via an organ called the funiculus. This organ is like an umbilical chord that attaches human babies to their mothers. When you open up a plump pea pod to scoop out the fresh green peas, the funiculus is what attaches the peas to the inside of the pod.
So next time you are out in the garden collecting seeds, use this as one indicator for whether the seed is ready to store or needs to dry down in the house some more. Happy seed-saving!