How to Measure and Fix Soil pH
Why it matters, how to test it, and how to correct it safely.
A plant can be watered and fed correctly and still struggle if the soil pH is off — nutrients become chemically locked out of reach for the roots. Testing pH takes minutes and rules out a cause most growers never check.
Testing & Fixing pH
Mix a soil sample with distilled water, dip a pH strip, compare colour to the chart. Cheap and fast, slightly less precise.
Push a digital pH probe into moist soil for a direct reading. More accurate for repeated checks over time.
Elemental sulfur or peat moss worked into the topsoil, or an occasional dilute vinegar-water solution. Retest after 2–3 weeks.
Garden lime or crushed eggshells mixed into the topsoil, acting slowly over several weeks.
Ideal pH by Plant Type
Most tropical houseplants: 6.0–7.0. Ferns and Calathea: 5.5–6.5 (more acidic). Succulents and cacti: 6.0–7.5 (tolerate a wider range). If unsure, aim for neutral (~6.5) — it suits the vast majority of common houseplants.
pH FAQs
Why does soil pH matter for houseplants?
pH controls how easily roots can absorb nutrients. Even if the soil has enough nitrogen, phosphorus, and potassium, a pH that's too high or low can 'lock out' those nutrients so the plant can't use them — showing up as deficiency symptoms despite adequate feeding.
What pH do most houseplants prefer?
Most tropical houseplants do best in slightly acidic soil, around pH 6.0–7.0. A few specialists differ: succulents and cacti tolerate a wider range (6.0–7.5), while acid-lovers like ferns and calathea prefer 5.5–6.5.
How do I test my soil's pH at home?
Cheapest option: paper pH test strips — mix soil with distilled water, dip the strip, compare to the colour chart. More precise: a digital soil pH meter probe, pushed directly into moist soil. Avoid tap water when testing, since it can skew the reading.
How do I lower soil pH (make it more acidic)?
Add elemental sulfur, peat moss, or a diluted vinegar-water solution (1 tsp per litre, occasionally) to gradually lower pH. Make changes slowly and retest after 2–3 weeks — large swings stress roots.
How do I raise soil pH (make it less acidic)?
Add garden lime (calcium carbonate) or crushed eggshells worked into the topsoil. This works slowly over weeks, which is safer for the roots than a fast correction.
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Track soil changes over time
Log pH tests and amendments in your diary to see what actually moved the needle.
