Southland's growing season is the shortest and coolest in New Zealand, and its frost record shows something no other region on this list can claim: there's no reliable frost-free stretch at all. Invercargill's own data shows ground frost recorded in every single month of the year on average, even January and February, which means a Southland garden can't be planned around a "last frost date" the way the rest of the country can.
That doesn't rule out a genuine spring garden, it just changes the approach. Cold-hardy crops, lettuce, spinach, silverbeet, peas, beetroot, carrots, dwarf beans and swede, go in from September and tolerate a light frost without much trouble. Anything genuinely frost-tender, tomatoes, capsicums, courgette, basil, is safer started and grown on undercover, in a greenhouse, cloche or cold frame, until at least November and ideally later, rather than trusted to open ground on the strength of a warm week.
A greenhouse or even a simple tunnel makes a bigger difference to what a Southland garden can grow than almost any other single investment, since it sidesteps the frost problem entirely for the crops that need it most. For everything else, keep an eye on the forecast right through spring and into early summer rather than assuming the risk has passed once the calendar says November: a clear, cold Southland night can still turn up with very little warning.
A greenhouse or even a simple tunnel makes a bigger difference to what a Southland garden can grow than almost any other single investment, since it sidesteps the frost problem entirely for the crops that need it most.