Wrong soil pH
pH decides which nutrients a plant can reach. Most crops grow best around pH 6.5; blueberries need it much lower. In the wrong range, nutrients lock up, leaves yellow, and feeding does little.
Soil & nutrients
What it looks like
pH problems look like deficiencies that will not go away.
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Chlorotic acid-lovers Blueberries and camellias yellow between the veins on chalky soil. -
Hydrangea colour Blue hydrangeas turn pink in alkaline soil; pink ones blue in acid. -
Scabby potatoes Common scab is worse in alkaline or freshly limed soil. -
Clubroot on acid soil Brassicas on acid soil are more prone to clubroot.
How to confirm it
A test is cheap and certain.
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Test several spots
Use a kit on soil from a few places, 10 cm (4 in) down, and average the result.
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Compare with the plant
Most vegetables: 6.0 to 7.0. Blueberries: 4.5 to 5.5. Brassicas: 6.5 to 7.5.
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Wait after liming
Test more than three months after adding lime, fertiliser or manure.
What to do
Change pH slowly, or change the plant.
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Raise pH
Add garden lime in autumn at the rate the test suggests to sweeten acid soil.
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Lower pH
Work in sulphur chips, and use rainwater and ericaceous mulch; change is slow.
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Use containers
Grow acid-lovers in pots of ericaceous compost where the soil is alkaline.
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Choose suited plants
On strong chalk, grow what likes it rather than fighting it.
Prevent it next time
- Test before planting long-lived crops like blueberries and asparagus.
- Lime brassica beds on acid soil ahead of planting.
- Keep lime and mushroom compost away from acid-loving plants.
What not to do
Do not lime and manure the same bed at the same time; they react and waste nitrogen.
In the growing guides
Where the guides mention it, with plant-specific advice.
Sources
- Soil: understanding pH and testing, Royal Horticultural Society
- Chlorosis, Royal Horticultural Society