Hi Peatpod
I gather you are talking about the red amaranthus.If you wait until the "flower" head turns brownish,you will see the seed,,just cut it off and put into a bag.With a good shake the seed will fall out,and I just dump the seed on a tray for a few days.I find the seed stays viable for years and this plant self seeds readily.I spilled some seed in my gravel driveway 3 years ago and I am still getting plants popping up.
Mollyzone5.

Thank you so much for the info Molly .. I am worried that we will have a cold snap and I will lose the seeds .. would that affect them?? The flower heads are beginning to slowly turn color .. would they be viable if I removed and dried the flower head off the plant??

Laura