Blanching and Heat Sensitivity, Not Spacing, Set Cauliflower Apart
Oklahoma State University Extension gives one unified spacing table for broccoli, cauliflower, and cabbage -- "18 inches apart in the row with rows two to four feet apart" -- so the numbers genuinely don't distinguish cauliflower from its brassica relatives.
What does distinguish it: blanching. Ohioline (Ohio State University Extension), University of Maryland Extension, University of Illinois Extension, and Oklahoma State University Extension all describe gathering and tying a cauliflower plant's outer leaves over the developing curd once it reaches roughly 1.5 to 3 inches across, to block sunlight and keep the head from discoloring. Self-blanching varieties exist too -- cultivars bred so their leaves naturally curl inward over the curd, reducing or eliminating the need to tie them by hand.
Cauliflower is also more heat- and temperature-sensitive than its relatives. Oklahoma State University Extension calls it "more sensitive to a dry soil and to fluctuating temperatures" than broccoli or cabbage and names it "the more difficult to grow" of the three; Ohioline gives an optimal range of 60-65°F, with temperatures above 75°F risking "buttoning" -- a stunted, undersized head.
Why Spacing Matters for Cauliflower
Because cauliflower's spacing needs mirror broccoli and cabbage almost exactly, spacing itself isn't the lever that determines success with this crop -- temperature timing and blanching technique are. Plant it at the same spacing as broccoli and you'll be fine on that front; the plant is far more likely to fail from heat stress at head-formation time than from crowding.
Adequate spacing still matters for the blanching step itself, though -- leaves need room to be gathered and tied up over the curd without tangling into a neighboring plant's head.
