Auckland's last frost risk is early and mild by New Zealand standards: ground frost is essentially gone by September, and even June and July, the coldest months, average under two frost days each. For most Auckland gardens the real obstacle to an early spring planting isn't cold, it's the clay-heavy soil common across much of the region, which holds water long after a North Island nor'wester has dried out lighter ground elsewhere.
Raised beds or a season of added compost make a genuine difference here, particularly for root vegetables like carrots and beetroot, which sit and rot in waterlogged clay rather than sizing up. Lettuce, spinach, silverbeet, peas, dwarf beans and spring onion are all forgiving enough to go in from September regardless, along with parsley, coriander and mint.
Hold tomatoes, capsicums, cucumber and courgette until conditions have properly settled, usually by October, and expect the growing season to move fast from there. Auckland's warm, humid summer means these crops rocket once they're established, but the same humidity brings blight and powdery mildew pressure earlier than gardeners further south will see it. Good airflow between plants matters more here than almost anywhere else in the North Island.
Hold tomatoes, capsicums, cucumber and courgette until conditions have properly settled, usually by October, and expect the growing season to move fast from there.
Basil is worth calling out on its own: it's one of the more frost-tender herbs, and Auckland is one of the few regions where it can reliably go outside as early as September rather than waiting for November.