I know it's hard to believe since the summer solstice is tomorrow, but it's time to start your fall transplants for the fall vegetable garden. While a lot of fall vegetables (kale, spinach, lettuces, turnips, etc.) can be started from seed in the garden, a number of vegetables (broccoli, brussels sprouts, cabbage, cauliflower, collards and celery) must be started now, in order to have transplants available in the first weeks of August. For more information on starting seeds, see the Home and Garden Information Center's video on seed starting.
Referring to the Home and Garden Information Center's publication HG16 and using broccoli as an example, broccoli transplants can be planted in the garden in late July through the first three weeks of August. Since it takes five to six weeks to raise broccoli from seed to transplantable size, starting broccoli seeds now will produce broccoli transplants in the last week of July or the first week of August.
For more inquisitive gardeners, here are the particulars of how to calculate when you should start your fall transplants. First, pick a date when you want to start harvesting your fall broccoli or use the first frost date in your area, say you want to start harvesting on October 10 and continue to harvest side shoots throughout the fall. From October 10, subtract 14 days for so called short day factor (after the summer solstice, the period of daylight each day shortens so plants don't grow as fast). You also need to take into account the suggested number of days it takes to raise the broccoli from transplant to maturity. In the case of the premium crop broccoli I'm growing this fall, it's 55 days from transplant to maturity. So that means the transplants should go in the ground 69 (14 + 55) days prior to my October 10 harvest date or about August 2. Since it takes five to six weeks to get broccoli from seed to transpantable size, subtract that number of days from the August 2 date (I'll use six weeks or 42 days in my example), so you should start your seeds on June 21. The formula is, harvest date minus short day factor (14 days) minus days to maturity minus days to grow from seed to transplantable size equals seed starting date.