Brassicas — what the family shares
Quick answer. The brassicas are the only family in this library that FAO names specifically in its balanced-fertilisation guidance: for cabbage, cauliflower and crucifers in many areas the components are N, P, K, S and B. Sulphur and boron joining the usual three is the fact that defines this family. Boron, however, must never be applied without soil and water analysis — local irrigation water may already carry more than the crop needs.
What unites this family
Two things — one from the source, one structural. From FAO: the addition of sulphur and boron to the standard nutrient set, a family-specific statement that does not apply to the leafy or fruiting families. Structurally: three of the four members build a large leaf frame and then convert to a compact harvested organ — a head, a curd, a flower head. That conversion is a distinct stage, and nitrogen carried into it delays or spoils the conversion.
The pattern is therefore: nitrogen-led frame building, then a deliberate reduction as formation begins, with potassium supporting fill.
Where its members differ — and why this page is not enough
Kale is the exception that proves the rule: it has no formation stage at all, so it is managed like a leafy crop while keeping the family's sulphur and boron profile. Cauliflower is the least forgiving — a single curd, and any check at transplanting shows up in it weeks later. Broccoli produces side shoots after the main head, a second production period the others do not have. FAO also names a disorder in only one member: whiptail in cauliflower, associated with molybdenum deficiency.
Read the individual crop guide before acting. Applying cabbage's mid-season nitrogen reduction to kale would cut a leaf crop off for no reason.
The mistake this family invites
Applying boron because the family is known to need it. FAO names boron for crucifers and requires deficiency to be confirmed before boron is applied — the margin between sufficiency and toxicity in boron is narrower than for any other nutrient here, and Kuwaiti irrigation water can be boron-rich. Family membership is a reason to test, not a reason to apply.
Crops in this family
- Cabbage
- Cauliflower
- Broccoli
- Kale
Each has its own guide in the crop library, filtered by family.
Before acting on a symptom. Hollow or corky stem tissue, internal browning and whiptail all appear in this family and are associated in the literature with boron or molybdenum. Association is not diagnosis. Confirm by soil and water analysis before applying either — both cause damage in excess. A visual symptom alone is not a confirmed diagnosis.
Sources
FAO — Fertilizer and Plant Nutrition Bulletin 16, Chapter 6 (balanced fertilisation for cabbage, cauliflower and crucifers: N, P, K, S and B; Table 29 removal figures, Tandon 2004), Chapter 3 (whiptail in cauliflower and molybdenum), Chapters 4 and 7. Accessed 27 August 2026. No rate, planting date or irrigation quantity is stated.
Last reviewed 27 August 2026