Utah's alkaline soil — and what to do about it — print version.
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SUS Farms · Utah Gardening
Utah's alkaline soil — and what to do about it
soil · beginner · ~6 min read
Most Utah soils run pH 7.4–8.4 because of caliche — calcium-carbonate parent rock left over from ancient lake beds. The most common Utah-garden problem we see, by a wide margin, is iron-deficiency yellowing on tomatoes and peppers. The fix is rarely "add fertilizer." It's "lower the pH so the iron that's already there can dissolve."
How to test
USU Extension runs a soil-test mailer service for $20 that returns pH, EC, organic matter, P, K, and recommendations specific to Utah. Order kits at extension.usu.edu/usuanalyticallaboratory. Home-test strips work for ballpark, but the lab data is what amendments should be based on. Test before you plant a perennial bed; test every 3 years on annual beds.
How to lower pH
Elemental sulfur is the most reliable amendment, but slow — soil bacteria oxidize it to sulfuric acid over 4–8 months. Apply 1 lb per 100 sq ft to drop pH 0.5 unit, work into the top 6 inches, water deeply, and wait. Don't expect results in the same season. Aluminum sulfate works faster but is expensive at scale and is hard on soil biology.
How NOT to lower pH
Gypsum loosens caliche soil but does NOT change pH — that's a stubborn myth. Vinegar burns roots and the acidity doesn't persist past the next rain. Pine needles barely move the dial. Coffee grounds are fine compost but neutral by the time they finish breaking down.
Foliar iron for emergencies
When tomatoes show yellow-veined leaves mid-July, you need a rescue. Iron chelate (Sequestrene 138) sprayed at label rate on the leaves greens up plants in 3–5 days. It's not a fix for the soil, just a band-aid until the sulfur amendment kicks in next year.