Which deficiency causes cabbage to appear purple on the bottom?

The appearance of purple coloration on the bottom of cabbage is typically indicative of a phosphorus deficiency. Phosphorus is a crucial nutrient for plants, playing a key role in energy transfer and genetic information transfer through ATP (adenosine triphosphate) and nucleic acids. When phosphorus is deficient, plants may struggle to perform essential functions, resulting in stunted growth and distinct coloration changes.

In the case of cabbage, the leaves may develop a purplish hue due to limited phosphorus availability, which disrupts proper plant development. This condition is often exacerbated in cooler temperatures, which can reduce phosphorus uptake by the roots.

Other nutrients like potassium, nitrogen, and calcium contribute to plant health as well but do not typically produce purple coloration in cabbage. It's important to understand the specific roles of these nutrients in plant physiology to accurately diagnose nutrient deficiencies and their associated symptoms.