How to Raise or Lower Soil pH

Lime and sulfur calculator

Enter your area, current pH and target, and pick your soil texture. The result stays hidden until you press the button.

What soil pH means

pH 7 is neutral; lower is acidic and higher is alkaline. The scale is logarithmic, so each whole number is a tenfold change in acidity^[1][2]. Most vegetables do well between pH 6 and 7^[2].

Oregon State University puts most vegetables at pH 6–7, and blueberries, azaleas and rhododendrons at 4.5–5.5^[2]. Set your target to the plants you’re growing, not to a round number.

Soil pH classes

The USDA splits soil reaction into 11 named classes, from ultra acid below pH 3.5 to very strongly alkaline above 9.0, with neutral at 6.6–7.3^[3]. A soil test often names your class; the table gives each one’s range.

Test before you treat

A lab test is the accurate way to read pH and get a rate^[1]. To check at home, mix soil with an equal amount of distilled water into a slurry, wait 15 minutes, stir, then measure with litmus test strips or a digital pH meter^[1].

How to lower soil pH

Elemental sulfur lowers pH. The rate depends on your starting pH, how far down you want to go, and your texture. Pounds of elemental sulfur per 1,000 sq ft, as sand / loam / clay^[1]:

• Add no more than 15 lb per 1,000 sq ft in one application; wait 6 months and re-test before adding more.^[1]
• Mixing the sulfur into the soil speeds the reaction.^[4]
• Compost is slightly acidic and helps a little, but on its own it is unlikely to correct an alkaline soil.^[1]
• Yellowing new growth is a common sign of alkaline soil, where iron is hard for plants to reach.^[1]
• Calcium-rich soils, common in the West, resist change^[1]; where the soil contains free lime, lowering pH with sulfur at field scale isn’t practical.^[4]

How to raise soil pH

Ground limestone or dolomite raises pH. With no lab test, UC’s starting rate to raise pH about one point is 20 lb per 1,000 sq ft on sand, 45 on loam and 90 on clay loam; re-test after a year^[1].

• Use dolomite where the soil also lacks magnesium; ordinary limestone supplies only calcium.^[1]
• Wood ash and hydrated lime can work but are easy to misapply; limestone or dolomite is the safer choice.^[1]
• For a product that isn’t pure limestone, adjust for its calcium carbonate equivalent (CCE): product needed = recommended limestone × 100 ÷ CCE. If 11–20 lb per 100 sq ft is recommended, split it into two applications 6 months apart.^[5]
• Incorporate lime 6–8 inches deep before planting.^[5]

Be patient

You can always add more later, but you can’t take it back out, so start with the rate above and let it work^[1]. Test once a year, in the same season each time, and adjust from there.

pH by soil texture

Texture doesn’t fix pH. Across USDA-classified US topsoil, both the sandy and the clay ends of the scale run acidic, neutral and alkaline. Here is how each texture’s acres split across the three reaction groups^[3][6]:

Sand leans acidic (69% of its acres) and clay leans alkaline (55% of its acres), but both cover all three groups, so test before you reach for lime or sulfur. Acidic soils usually need lime to come up; alkaline soils need elemental sulfur to come down.^[6][3]

Texture also decides how much amendment you’ll need. A sandy soil shifts pH with far less material than clay because it buffers less: UC’s starting lime rates run 20 lb per 1,000 sq ft on sand versus 90 on clay loam^[1].

Color is no shortcut either. The red of red clay comes from iron oxides, not acidity^[7][8], so test a red soil like any other. For the rest of working red clay, see amending clay soil.

Soil pH across the US

Acre-weighted across USDA’s classified US topsoil, surface pH splits across the USDA reaction classes like this^[3][6]:

By state, the most acidic and most alkaline topsoils (acre-weighted median surface pH, among states with at least 500 components carrying a mapped surface pH):^[6]

The most acidic topsoils sit in the humid Northeast and Southeast; the most alkaline sit in the arid West and Great Plains^[6]. See where your own address falls on the soil pH map.

Download the data: pH reaction classes (CSV), median pH by state (CSV). Figures aggregated from USDA SSURGO; data generated 2026-10-07. See the methodology for how it’s computed.

Frequently asked questions

How can I lower soil pH quickly?

There’s no fast, safe way: sulfur works over months. Add no more than 15 lb per 1,000 sq ft at a time and re-test after 6 months.^[1]

How much lime do I need per acre?

As a no-test starting point to raise pH about one point, UC’s rates work out to about 870 lb per acre on sand, 1,960 on loam and 3,920 on clay loam^[1]. For fields, use a soil test’s lime recommendation.

How do I use pelletized lime?

Check the CCE on the bag: product needed = recommended limestone × 100 ÷ CCE.^[5]

How long does lime take to work?

It reacts slowly; UC suggests re-testing after a year.^[1]

Should I use dolomite or limestone?

Use dolomite where the soil also lacks magnesium; ordinary limestone supplies only calcium.^[1]

Is red clay soil acidic?

Not because it’s red. The red comes from iron oxides in the clay, not from pH^[7][8], so test it rather than going by color, and see amending clay soil for the rest.

Does soil texture set the pH?

No. Across US topsoil, 69% of sand acres are acidic while 55% of clay acres are alkaline^[3][6], so both textures run the full range. Sandy soils also shift with less lime or sulfur than clay, because they buffer pH less^[1].

How this calculator works

Texture mapping is our own: the site’s sandy group reads the sand column, loamy reads loam, and clay-rich reads clay (and the clay-loam rate for lime). For lowering, the calculator reads the sulfur table above: if your current pH falls between rows it uses the next lower row, and if your target falls between columns it uses the next higher column (both choices ask for less sulfur), and the result says which cell it used^[1]. A current pH below 5.5 or above 8.0, or a target outside 5.0–7.0, is outside the table, so it points you to a lab test instead.

Next steps

Changing pH is one branch of the step-by-step plan to improve garden soil. For the materials themselves, see the soil amendments guide.