Soil basics

Understanding your soil's pH

If you only ever learn one number about your soil, make it this one. pH measures how acidic or alkaline your soil is, on a scale from 0 to 14 — 7 is neutral, lower is more acidic, higher is more alkaline. Most garden soil lands somewhere between 5 and 8.

Why it matters

pH controls whether the nutrients already in your soil are actually available to your plants. Iron, for example, becomes very hard for plants to take up once soil pushes above about 7 — which is why a shrub in alkaline soil can sit next to a bag of fertilizer and still starve. You can't out-fertilize the wrong pH.

Most annuals, perennials, and vegetables are happiest in the slightly acidic range of about 6.0 to 7.0. A few acid-lovers — blueberries, azaleas, and hydrangeas you want to bloom blue — prefer things much lower, down around 4.5 to 5.5.

Finding out where you stand

Inexpensive home test kits and probes will get you in the ballpark, and they're fine for casual checking. For a reading you can act on, a lab soil test is worth every penny — the University of Minnesota Extension runs an excellent, affordable one that also tells you your organic matter and nutrient levels.

Moving the number

• To lower pH (make soil more acidic): elemental sulfur is the steady, garden-friendly tool. It works slowly — soil microbes have to convert it — so apply in fall for next season and don't expect overnight change.
• To raise pH (sweeten acidic soil): garden lime, worked in ahead of planting. Again, months, not days.
• Either direction: compost and organic matter act as a buffer, nudging soil toward that happy middle zone and holding it there.

The biggest mistake we see is impatience — dumping on amendments, retesting a week later, and adding more. Adjust modestly, give it a season, and retest. Soil moves slowly, and that's a feature: it means it's stable once you get it right.

Not sure where to start? Bring your soil test results into the greenhouse — we read them all the time and we're happy to translate.