Ask any experienced New Zealand gardener when to plant tomatoes and most will say the same thing: Labour Weekend, the fourth Monday of October. It's one of the most widely repeated pieces of gardening advice in the country, and unlike a lot of garden folklore, this one actually holds up. It isn't really about the date itself, it's about what the date is standing in for: by late October, most of the country has cleared its main frost risk, and tomatoes are frost-tender enough that a single cold night can kill a young plant outright.
The rule works because Labour Weekend happens to land close to the real last-frost timing for a wide band of the country, Waikato, the Bay of Plenty inland, Manawatū, Nelson and Marlborough among them, where frost risk typically eases through November. For those regions, "wait for Labour Weekend" is close enough to "wait for your actual last frost" that the shortcut is genuinely useful.
It's the wrong rule everywhere else, though, and by a meaningful margin in both directions. Auckland's frost risk usually clears by September, roughly two months earlier, and gardeners there who wait for Labour Weekend are simply giving up free growing time for no reason. At the other end, Canterbury's frost season often runs into December, later than anywhere else in the country with a genuine frost-free season, and Southland's frost risk barely clears at all in an average year. Planting tomatoes on Labour Weekend in Christchurch is planting into real frost risk more years than not.
It's the wrong rule everywhere else, though, and by a meaningful margin in both directions.
The honest version of the rule is this: Labour Weekend is a genuinely good estimate for the middle band of the country, and a starting point worth adjusting from everywhere else, earlier in the far north, later the further south and inland you go. Whichever week you land on, the actual test is the same everywhere: has your region's last frost genuinely passed, not just has the weather been warm for a few days. A tomato planted a week late loses almost nothing. A tomato planted into a late frost is usually planted twice.