When to plant biennial vegies in Zone 9?

I am living in NZ where we have occasional frosts down to -3C, but also temperatures up to 14C during the day.

It is the shortest day in a week's time in the Southern Hemisphere.  What is it that triggers biennial vegetables to go to seed?  Is it cold weather or the shortening and then increasing days?  If I plant biennial seeds after 21st June 2025, will they not go to seed till spring 2026?  

So I'm just refreshing my memory of familiar light frost hardy biennials as I'm in a similar climate to you:

Alliums (Garlic, Onion, Leek);
Asteraceae  (Lettuce, Salsify etc.);
Beet family (Beetroot, Chard, Spinach etc.); Brassicas (Broccoli, Brussels sprouts, Cabbage, Cauliflower, Collards, Kale, Mustard, Turnip etc.);
Umbellifers (Parsley, Carrots, Parsnip etc.).

I think they're all going to have slightly different needs.

But I think generally you'd start the seeds around the equinox, and for non-roots, potentially transplant (or plant bought plants) before the average first frost?

"But I think generally you'd start the seeds around the equinox, and for non-roots, potentially transplant (or plant bought plants) before the average first frost?"


Thanks for the reply.  Are you writing this for the northern or southern hemisphere?  We are almost at the shortest day  (21st June).  The gardening tradition here is not to plant pumpkin and other frost sensitive plants till the end LAbour day (end of October) as frosts are very unlikely after that.  But highs of 13C or more are common mid winter as well as light frosts.  The average high in midsummer is 23C, we are very temperate here.