In article , sam
writes

Alas,cardboard is made from wood,which depletes the soil of nitrogen.I
was similarly caught out last year using "peat" pots, only to learn
later that they are now 80% wood chippings.

Not likely to trouble peas which are adapted to low nitrogen conditions
by developing the ability to 'fix' free nitrogen
--
Kay
"Do not insult the crocodile until you have crossed the river"