A Second Chance for Broccoli

If you were disappointed by your broccoli, cauliflower, or romanesco harvests this spring, good news – you have a second chance this year with a fall crop! Although we are just getting into what many consider the “taste” of summer with our first tomato, ground cherry, and zucchini harvests, July is the time to start planting fall crops. While it may be difficult to think about fall crops before Labor Day, Chicagoland doesn’t have quite enough long, warm days between Labor Day and the first frost to put off starting most fall crops after summer has nearly ended.

'Snowball' cauliflower in 2015.

‘Snowball’ cauliflower in 2015.

This is also a good time to familiarize yourself with the information on your seed packet to best calculate seed starting dates for fall crops:

Days to germination – this is the average number of days it takes for the seed to germinate. Sometimes a temperature range will accompany this information. Generally, seeds germinating at warmer temperatures will germinate faster than seeds at cooler temperatures, until a point. When temperatures are higher than 90 degrees, many plants will lie dormant until it cools off, and vice versa for temperatures below about 60 degrees.

Weeks to transplant – this is the average number of weeks after germination it is recommended to grow indoors until the seedling can be transplanted outside. In the spring, this is typically sometime around the last frost date in late April/early May to avoid frost damage on tender plants and to give them a head start on growth before summer’s heat kicks in. In the summer, this is to give the gardener time to get a head start on growing seedlings while there may not yet be space in the garden for fall crops, and to allow plants to develop strong root systems before entering a hotter and drier outdoor environment. Four-to-six weeks after germination is a good time to transplant. Don’t forget to spend 5-7 days hardening off your plants before transplanting.

Days to maturity – this is the average number of days after transplant that it will take the plant to reach harvest size. This number is often confusing to gardeners, who mistake it for the number of days to harvest after planting the seed. This is commonly why gardeners may have plants that are too young and too small to produce a harvest before the first frost date in late October/early November.

Although the short day factor is almost never on seed packets, it’s important to consider that as we head toward the fall equinox, days are now growing shorter. Crops maturing in the fall need an average of two more weeks to reach harvest size than the same crops maturing in late spring, as they are reaching maturity during progressively shorter day lengths and cooler temperatures.

Broccoli heads forming, about a week from harvest.

Broccoli heads forming, about a week from harvest.

To calculate a fall seed starting date for ‘Calabrese’ broccoli, first decide when you would like to harvest it. At the latest, choose a harvest date before the first average frost date, which is around Halloween. Your seed packet may only contain days to germination and days to maturity, so be sure to fill in the other information as discussed above.

Days to germination: 3-10 days
Hardening off period: 5-7 days
Weeks to transplant: 4-6 weeks (28-42 days)
Days to maturity: 58
Short day factor: 2 weeks (14 days)

Under optimal growing conditions, ‘Calabrese’ broccoli in Chicagoland can be expected to be harvested as soon as 108 days after starting from seed, and up to 131 days.

Now, count backwards your chosen harvest date to determine your seed starting date. This tells us to start seeds on July 9 for a mid-October harvest.

Other dates to mark on the calendar:

Week of August 6: begin hardening off broccoli seedlings
Week of August 13: transplant broccoli seedlings with fertilizer
Week of September 17: side dressing of fertilizer, begin heavier watering
Week of October 15: begin examining broccoli heads and harvest if ready. Harvest after the heads have stopped growing in diameter (but are still tightly held buds) and before they begin to loosen and the buds start to open.

While correct calculation of a fall seed starting date is the first step to growing full-size heads of broccoli, cabbage, and other Brassicas, keep in mind that these plants are considered heavy feeders, and should get an all-purpose fertilizer at transplanting time and again 4-6 weeks later. They will need plenty of water, particularly around the time they begin to develop their heads. These plants also need adequate space to grow large – a single broccoli plant will grow about 2 square feet to produce an 8″ diameter head. In less space, keep in mind the plant will be smaller and produce a smaller head. Finally, make sure that the variety planted meets your expectations for growth – some varieties produce smaller plants (and thus, smaller heads) and may be more appropriate for a small garden.

written by Breanne Heath