Broccoli (Brassica oleracea var. italica)
“Broccoli” can mean different things to different people. When most people think of broccoli, they are thinking of sprouting broccoli (often referred to as “Italian” or “Calabrese” broccoli). “Heading” broccoli is not a broccoli at all — it is a late-season or overwintering cauliflower. Another broccoli, broccoli rabe or raab, does not produce a head and is used as a greens crop.
Temperature
Preferring cooler temperatures for growth, broccoli grows optimally at ranges between 60–70°F, however, it will still produce well in warmer conditions. Sow from seed in late summer to early fall, when soil and ambient air temperatures are in the high 60s and 80s, respectively; seeds will emerge within 7 days in these conditions. Ambient temperatures are a major contributor to when flower heads develop. In summer, heads maturing in July may bolt faster (4–6 days) when compared to those maturing in the spring and fall when the temperatures are cooler.
When broccoli is under stress, such as low temperatures, purpling of florets may occur. This is caused by an increase in the expression of anthocyanins, which is a plant secondary metabolite.
Spacing
The spacing of plants greatly influences yield and head size. Wider between-row and in-row spacing yields larger heads and an earlier harvest. Hollow steam disorder is more likely though, as the growth rate increases. Plant or transplant into rows that are 18–36 inches apart and 12–18 inches between each plant.
Soil
Plant in soil that is well-drained and has good water-holding characteristics. Broccoli grown on sandy soil will likely require irrigation. A slightly acidic soil of 5.8 to 6.6 is recommended.
Harvest
Harvest is determined by head diameter, anywhere between 4–6 inches, however, most often harvest starts when a majority of heads are 5 inches in diameter. Bunched broccoli has stalks between 5–8 inches in length. It is important to cool broccoli promptly following harvest. For the best quality, store it at 32°F with a relative humidity of 95–100%. Under these conditions, the storage life may reach 3 weeks or more. With longer storage time comes a loss in quality as firmness and coloration degrade. Broccoli can be stored above 32°F but it will significantly reduce storage life.
For more information, please see links below:
- Penn State Extension - Broccoli Production
- University of California - Broccoli Guide
- West Virginia University - Growing Broccoli
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