To know a plant, grow a plant!
Approximately 48 days after planting your Fast Plants seeds, you can be able to plant the seeds produced by your own plants!
This page describes what is involved in producing seeds that will germinate and produce an offspring generation. The time it takes to produce viable seeds is highly influenced by the environment in which you grow your plants.
For seeds to be produced, flowering and pollination must be successful. For Wisconsin Fast Plants, this results from cross-pollination. Self-pollination is not out of the question for WFP, but it is quite rare. Typically, pollen that lands on the stigma of flowers on the same plant that produced the pollen is aborted (consider how this is adaptive!) so if there is only pollen available from "self," no seedpod would develop at all (or seeds)--the flower would simply die off.
Consider the following scenario: If you have a single Fast Plant that was an early bloomer so there were never any other plants from which pollen was gathered to fertilize it (not even one other flower on another plant, perhaps later in the week) and you see seed pods developing, then you must have successfully accomplished some self-pollination (not unheard of, but pretty rare in Fast Plants). If seeds develop, they will not be sterile. The self-incompatibility inhibits fertilization; it does not affect seed development.
Use a Calendar: As soon as pollination begins, mark your calendar. Pollinate all flowers on all plants every-other-day for 1 week. The day you stop pollination and mark your calendar again.
Take drying plants off water: Approximately 20 days after last pollination, or when the ends of the pods are changing from green to brown, take your plants off water by removing the water reservoir. The pods pictured at left are just barely beginning to turn brown at the tips; they would be best removed from water in about 5 more days. (Note: if you leave your plants on water, your seeds may begin to germinate in the pods before you harvest them).
Seeds cannot germinate before they are mature: When seeds mature, they develop the embryo that is contained within and the stored energy and matter it will need to grow into a young seedling. You can tell when this is happening if you monitor your seeds. They will change from being soft and "squishable" to firm.
In addition to watching for pods to brown and dry, you can check your seeds' maturity: Open a seed pod that is average in size and maturity, observe the seed size, and pinch several seeds. If the seeds are firm and larger than what is typical of dried seeds (they will shrink as they dry) then most of your seeds are likely mature and ready to be dried. The seeds pictured on the right are getting close, but the pods are just beginning to turn brown -- a few more days on water would be best.
Drying and Harvesting: Seeds need to mature and dry in their pods. Leave your plants under the lights to dry after you take them off water, and when the pods become brittle, you're ready to harvest. Suggestions for how to harvest Fast Plants seeds can be found here.
Storing Seed: Fast Plants seeds--either produced by you or purchased--will stay viable for years if they are stored cold and dry. Seeds placed in a mason jar with a small packet of silica (like comes packed with shoes or other items) and stored in your freezer can retain their vigor for several years.