In article BfF8d.5586$Xk1.2877@trnddc02, Den writes
This is a really basic question I suspect - forgive my ignorance!

I have a pack of mustard seeds. How do I 'keep them going', so that I don't
get one crop of mustard and then have to buy a new packet of seeds?

Mustard plants will develop seed heads if they are left in place for
long enough without being cropped. The seed can then be collected and
used for future sowings. Or they could just be left to drop their seeds
and some new plants will grow in their own time and place.
--
Alan & Joan Gould - North Lincs.