Red seed will create heat resulting in a wilted and damaged fern. A small amount, usually, is acceptable, but no more than one third of the fern. Buyers usually do not like to seed red seed or heavy seed. Too much seed and you risk rejection by the buyer.
Seed stage lasts for a short time. The seed then falls off creating a dusty film. The dust is actually spore that will create next year's crop. Remember, when picking ferns, leave one or two ferns per stool to insure a crop for next year.