I know we aren't even at the summer equinox yet, but its time to start thinking about starting fall broccoli and cauliflower. Here's the scoop, work backward from the date you want to harvest your crop. Let's take my favorite fall broccoli (Premium Crop produces lots of side shoots right up until it gets frozen out).
Say I want to harvest the central head around October 15 . The seed starting date can be calculated by subtracting from the October 15 date, 14 days for fall's short day factor, the days to maturity for the fall crop, the time to raise seedlings to transplantable size and the days for the seeds to germinate. For example, from October 15 I would subtract 14 days for the short day factor, 60 days for the days to maturity from transplant, five weeks to six weeks for raising seedlings to transplantable size (35 to 42 days) and 5 to 7 days for seed germination.
To make the calculation, I just plug these numbers into an Excel spreadsheet and get a seed starting date of June 14. (I'm already behind). So, moving forward from today's date (6/19) my seedlings will emerge in about a week and be ready to transplant the first week of August. My premium crop broccoli will be ready to harvest in mid to late October, all the way to freeze up in December.
By following the simple equation outlined above, you can calculate the seed starting date for all of your fall transplants. And for more information on starting seed for transplants, see the seed starting videos on HGIC's Youtube site.