How does pH affect nutrient availability in most horticultural soils, and what pH range optimizes availability for most plant species?

• A. pH has little effect on nutrient availability; optimal range is 4.5-5.5
• B. pH alters solubility and uptake; most nutrients are optimally available at roughly 6.0-7.0
• C. pH only affects micronutrients; optimal range is 8.0-9.0
• D. pH directly changes plant hormone production; optimal range is 3.0-4.0

Answer: (B)

Soil pH controls how nutrients exist in the soil water and how readily roots can absorb them. When pH is too low (acidic), some nutrients become highly soluble, but others—especially phosphorus, calcium, and magnesium—can become less available because they precipitate or bind to soil particles. When pH is too high (alkaline), micronutrients such as iron, manganese, zinc, and copper become less available, and phosphorus can again become less soluble. This means the overall availability of many essential nutrients swings with pH.

For most horticultural soils and most plant species, a near-neutral to slightly acidic range provides the best balance. Around 6.0 to 7.0, nutrients tend to be sufficiently soluble for uptake while avoiding extreme immobilization or toxicity, supporting healthy root function and nutrient absorption. Some plants do prefer different conditions—blueberries and other ericaceous plants, for example, thrive in more acidic soils—but the general pattern for the majority of crops is that pH modifies solubility and uptake, with about 6.0–7.0 offering the broadest nutrient availability.