Lime vs Sulfur: How to Raise or Lower Soil pH the Right Way

Use lime to raise soil pH and elemental sulfur to lower it, but only after a soil test shows you need to, and let the lab report set the rate. Both are slow: lime usually takes months, and sulfur can take a year or more. If your soil contains free lime, as many Western soils do, lowering the pH is rarely practical.

Soil pH controls how available nutrients are to roots. Phosphorus, for example, becomes less available when pH falls below 6.0 or rises above 7.3. That is why a pale, unhappy plant may be sitting in soil with plenty of nutrients it can’t use. It is also why guessing is risky, since moving pH the wrong way can cause the very symptoms you want to cure.

Do you need to change pH at all?

Probably less often than you think. Most plants tolerate a fairly wide range:

• Vegetables, grasses and most ornamentals: about 5.5 to 7.0, according to the University of Maryland Extension, which puts the ideal for most annuals, perennials and vegetables at 6.2 to 6.8.
• Azaleas, rhododendrons, blueberries and many conifers: about 4.5 to 5.5.
• Most landscape plants in high-pH regions: Colorado State University Extension calls 6.0 to 7.5 acceptable, with iron becoming limited around 7.5.

A lab test beats a home color kit, which can be inaccurate. The report also includes a buffer pH, which shows how strongly the soil resists change and sets how much lime it needs. Clay and high-organic soils need more lime than sandy soils to shift the same amount. Our guide on how to read a soil test walks through the numbers.

Lime vs sulfur at a glance

How to raise soil pH with lime

1. Confirm the need. Apply lime only if the test calls for it. Thin grass or moss alone is not proof, as our article on whether your lawn needs lime explains.
2. Pick the type. Use dolomitic lime when the report says both pH and magnesium are low. Otherwise calcitic lime is fine. Finer particles act faster, while pelletized lime spreads more easily and is less likely to clog a spreader.
3. Avoid hydrated lime. It is quick-acting but can burn plants if used incorrectly.
4. Spread evenly. Lime is very insoluble and moves little, so patchy coverage means patchy results.
5. Work it in if you can. In beds, blend it into the top few inches of soil with a fork or tiller.
6. Split big doses. If a lawn needs 85 pounds per 1,000 square feet, apply 50 now and the remaining 35 about six months later.
7. Retest. Wait a year for lime to react fully, then test again. An application that brings soil up to about 6.5 can last several years.

Wood ash can also raise pH. Maryland Extension treats about 2 pounds of ash as equal to 1 pound of limestone and says not to exceed 20 pounds per 1,000 square feet a year, based on soil test results.

How to lower soil pH with sulfur

1. Check for free lime. Put a little moistened soil in a dish and add a few drops of vinegar. If it bubbles, the soil contains free lime and sulfur won’t work well. Colorado State says it is often impractical to acidify these soils.
2. Use elemental sulfur. Iron sulfate is another option, but it contains far less sulfur. Avoid aluminum sulfate, because aluminum can be toxic to roots.
3. Use the right rate. Follow your lab report. As a guide to the scale, Oregon State University Extension lists 10 to 20 pounds per 1,000 square feet for sandy soil and 40 to 50 pounds for clayey soil west of the Cascades, while Wisconsin advises no more than 20 pounds a year. Don’t exceed what is recommended.
4. Mix it in. Work it into the top 6 inches and keep the soil moist but not saturated, since the bacteria need contact, water and warmth to do the work.
5. Acidify gradually. Two small applications a year apart are safer than one large one.
6. Retest. Colorado State suggests retesting three to four months after application. Oregon State found full results can take a year or longer, so test at the same time each year.

For shrubs already in the ground, sulfur is harder to apply because you can’t mix it in without cutting roots. Oregon State suggests working small amounts into several holes near the drip line. If new leaves are yellow with green veins, read our guide to iron chlorosis, which is often the visible result of high pH.

If your soil can’t be changed

Where soil is naturally alkaline with free lime, stop fighting it. Choose plants that tolerate your pH, or grow acid lovers such as blueberries in raised beds or containers filled with a suitable acid mix. It is usually cheaper and far more reliable than treating the ground year after year.

Safety notes

Never mix lime, sulfur, fertilizers or other garden products together. Apply them separately, follow the label, and store them away from children and pets. Wear gloves and eye protection with fine powders, and avoid spreading on windy days.

Bottom line

Test before you buy. Lime raises pH and sulfur lowers it, and the lab report should set the amount for either one. Plan ahead, because lime takes months and sulfur can take more than a year. If your soil has free lime, skip the sulfur and work with plants that fit your soil.

FAQ

How long does lime take to work?

Usually 3 to 9 months when mixed into moist soil. Lime spread on top of a lawn moves down slowly and may take 6 to 12 months to reach the root zone.

Can I apply lime and sulfur together?

No. They work against each other, and you should never mix garden products. A soil test will tell you which one you need, if either.

Can I change pH faster?

Not safely. Finer lime acts somewhat faster, but fast-acting hydrated lime can burn plants, and aluminum sulfate risks root damage. Slow, tested changes work better.

Should I lime my garden every year?

Not by default. Lime only when a soil test shows the pH is too low. Testing every few years is usually enough to catch a drift.