Canterbury holds onto frost longer than almost anywhere else in the country. On the plains around Christchurch, ground frost is still averaging more than five days a month through October, and most years it doesn't properly let go until December. That's a full two months behind Auckland, and it catches out a lot of gardeners who plant by a date they read somewhere else rather than by what's actually happening outside.
The nor'wester is the other thing Canterbury gardeners learn to plan around. A hot, dry gale can arrive with almost no warning in spring and flatten a bed of unstaked tomatoes or beans in an afternoon, doing more damage in an hour than a light frost would do in a week. Stake tall crops as soon as they go in the ground, not once they've grown tall enough to need it, and choose a sheltered spot against a fence or building if you have one.
Once both risks have genuinely passed, the planting itself isn't complicated: lettuce, spinach, silverbeet, peas, beetroot, carrots and dwarf beans can all go in from September, well ahead of the frost-tender crops. Tomatoes, capsicums, courgettes and sweetcorn are the ones worth waiting for. Canterbury's own last-frost timing sits around late November to December most years, and a plant that goes in a fortnight later than a North Island guide suggests loses almost nothing, while one planted a fortnight early can be wiped out overnight.
Once both risks have genuinely passed, the planting itself isn't complicated: lettuce, spinach, silverbeet, peas, beetroot, carrots and dwarf beans can all go in from September, well ahead of the frost-tender crops.
Garlic is worth a mention here too, even though it's a winter crop rather than a spring one: Canterbury's cold snaps are exactly what garlic needs to bulb up well, and gardeners further north often struggle to get the same result. If you missed planting it this year, it's worth remembering for next April.
Check this site's Christchurch planting calendar for the exact month range on any specific vegetable, since a handful, garlic among them, run on a different clock to the spring list above.