Blueberries need strongly acidic soil, about pH 4.5 to 5.5
Blueberries need strongly acidic soil, about pH 4.5 to 5.5. Above about 5.5 the soil is not acidic enough and the plant cannot take up iron, so the new leaves yellow between the veins (iron chlorosis). Test the soil before planting; if it is too high, lower it with elemental sulfur applied several months ahead, then re-test. A foliar iron spray only greens the leaves for a while and does not fix the soil.
Promising A person has checked it against its sources. If you skip this, it still grows, just less well. The planner suggests it.
How it works
Blueberries are acid-loving plants adapted to low-pH soils. At soil pH above about 5.5, iron is not available to the roots even when it is present in the soil, and the plant develops interveinal chlorosis (yellowing between the veins) on new growth. Lowering the pH with elemental sulfur makes iron available again; spraying the leaves with iron greens them only temporarily and leaves the soil, and so the plant's long-term health, uncorrected.
What to do about it
Test the soil pH before planting. If it is above about 5.5, lower it with elemental sulfur applied months before planting (ideally the season or the year before), and re-test before you plant. If the soil is near neutral (above about 6.0) and hard to acidify, choose a different site. Do not rely on foliar iron sprays as a cure; they mask the yellowing without correcting the soil.
How much it matters: No figure is stated. Above pH 5.5 the plants yellow, grow poorly and may die; within the 4.5 to 5.5 range they take up iron and thrive. Because siting, soil testing and acidifying are all the gardener's to do before planting, the rule only advises.
The evidence
Evidence: checked against 2 sources in the research-based literature.
The 2 sources
Do not plant blueberries until the soil is at the correct pH (4.5-5.5), or the plants may fail in the first year.
If the pH is above 6.0, select another planting site. If the soil pH is below 6.0 but above the 5.5 limit, apply wettable sulfur (90 percent sulfur)
Plants it applies to
How this rule has changed
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Cite this page
Milpa Gardens. "Blueberries need strongly acidic soil, about pH 4.5 to 5.5. Above about 5.5 the soil is not acidic enough and the plant cannot take up iron, so the new leaves yellow between the veins (iron chlorosis). Test the soil before planting; if it is too high, lower it with elemental sulfur applied several months ahead, then re-test. A foliar iron spray only greens the leaves for a while and does not fix the soil." Evidence grade: Promising. https://milpa.garden/rules/blueberries-need-strongly-acidic-soil-about-ph/
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