You could argue that since they are berries they eventually rot, but then you could say planters need water flasks as fuel to keep the other plants alive and we don’t want to go there.
I say the berries do indeed rot, but the plant producing the berries is kept alive by the planter thereby continuously replacing spoiled berries.
maybe something in the way berries spoil, they could turn into a small piece of fertiliser, and then enough of them, re-fertilise the soil - a bit like how fruit and leaves decompose back into nutrients that self-feed the plant in some way)
if you do play solo though, and are up to trying some savegame backups, and mods, i do recommend the farming mod - it may need an update following on from the october 2 part patches/hotfix though, but im still running without the hotfix with almost 50 mods)
oh ok, i didnt realise you were on xbox - my xbox 360 suffered the ring of red lights, twice - so after microsoft charging large amounts to supposedly fix it, and getting the same problem twice - i stopped xbox.
my original xbox (transparent plastic edition) still works fine though, so does my playstation 1