New World Little Gardens

How long do the inactivated seedlings last? I am keen to keep them till the beginning of next year for when I'm flatting, but there is no point if they are going to go off :)

The good news is that the seed mats and biodegradable pots are best before 12/03/2019 and the soil tablet is best before 12/11/2018.  These dates are also printed on the outer label of each seedling kit.