Soil Science
Soil pH
Soil pH is the master variable of horticulture. It dictates nutrient availability. You can dump kilos of fertilizer onto a bed, but if the pH is wrong, the plant cannot absorb it (nutrient lock-out).
The Optimal Range
Most plants prefer slightly acidic soil (pH 6.5) because this is the point where the maximum number of essential nutrients are soluble in the soil water.
Common Mistakes
- Applying lime without testing, driving pH up and locking out iron and manganese.
- Assuming ericaceous (acid-loving) plants will survive in neutral soil with just a top dressing of pine needles.
Data Points
| Amendment | Effect | Speed |
|---|---|---|
| Garden Lime (Calcium Carbonate) | Raises pH | Months |
| Elemental Sulphur | Lowers pH | Months (requires microbial action) |
FAQ
How often should I test?
Every 3-5 years, or whenever establishing a new bed.
Internal Links
- Calculate Lime/Sulphur
- Buffering pH with compost
- Tomato pH needs
- Potato scab and pH
- Rose pH preferences
- RHS Level 2 Soil Module
- Cation Exchange Capacity
- NPK availability
- Bed prep
- Mulch effects on pH
- Homepage
- Courses
- Guides
- Tools
- Seedling sensitivity
- Application timing
- Adjusting mix pH
- Compost acidity
- Leaching
- Study options