Should I put lime on my lawn in Iowa?
Why Iowa State University says most Iowa lawns do not need lime, the pH range turf and gardens grow best in, how buffer pH sets the rate, and why the soil temperature decides whether to lime this fall or next spring.
Only if a soil test says so. Iowa State University Extension says lawns grow best at a soil pH between 6.0 and 7.5, that lime is for soil below 6.0, and that few Iowa lawns are that acidic. Lime spread on soil that is already above 7.0 can push it too alkaline, which makes nutrients harder for grass to take up.
## Why most Iowa lawns can skip it
Iowa State's lawn answer is short: test first, and lime only when the test recommends it. Few Iowa lawns test below 6.0, so a bag of lime bought out of habit can do more harm than good. For vegetable and flower beds the target is a little narrower. Iowa State puts most garden plants at pH 6.0 to 7.0 and gives the same advice about testing before you lime.
## What the test has to show
A lime rate depends on two numbers. Soil pH tells you whether the soil is acidic. Buffer pH tells you how much lime it will take to move it, and Iowa State notes that a lab reports buffer pH only when liming may be needed. So a report with no buffer pH on it is a sign the lab did not see a need for lime.
Where it is called for, Iowa State's table gives pounds of pure, fine calcium carbonate per 1,000 square feet, worked into the top 6 inches. Two examples from that table:
- Buffer pH 6.5: 64 pounds to reach pH 6.5. - Buffer pH 6.0: 147 pounds to reach pH 6.5.
To scale the rate, multiply by your area in square feet and divide by 1,000. Most lime sold in Iowa is a mix of calcium and magnesium carbonates. Iowa State calls standard ground limestone slow but cheap and safe, and warns that hydrated lime works faster but is dangerous to handle. Bulk agricultural lime needs its rate adjusted for particle size and purity.
## Lime now or in spring
Iowa State says to apply lime in spring or fall while the soil is warmer than 55°F, and that working it in before planting is best. On an established lawn you can only spread it on the surface, so a large correction is split across several years. In mid-November, check the soil temperature with a probe thermometer before you buy anything. If it reads below 55°F, pull the soil sample now while the ground is open and plan to lime in spring once the report is back.
If the test shows the opposite problem, soil that is too alkaline for what you want to grow, Iowa State recommends elemental sulfur, which it says can take three to six months to act under warm conditions.
## Where to start
The Iowa soil testing steps on this site show which labs Iowa State points to, what goes in the sample bag and what the basic test reports, including pH, so you know before spring whether your lawn needs lime at all.