In article , Alan Holmes
writes

How long can you leave Swiss Chard in the ground?

How long can you keep cropping it for?

I planted some early last year and it is till cropping, do I need
to plant more?

Probably. In its second year it produces flower stems which are too
tough to be edible. You can keep taking these out, and pulling more
leaves, but you will lose the battle by midsummer. The determination to
flower increases, and the leaves that are produced get smaller and
smaller.
--
Kay
"Do not insult the crocodile until you have crossed the river"