Test Soil in Fall to Get Ahead of the Game in Spring
Published: Friday, October 17, 2025
Most every farmer and gardener has heard the value of soil testing and adjusting the pH of the soil to meet your crop needs. What you might not know is that when you apply lime or sulfur or other amendments to adjust pH, it often takes five or six months for the pH to move to towards the desired pH. That's why most farmers apply their amendments in the fall, to give the soil time to adjust.
As a basic review, pH is a scale that measures acidity and alkalinity. A pH of 0 is very acidic, a pH of 14 is very alkaline, with a pH of 7 being neutral. Most of our popular crops prefer a pH in the 6.2 to 6.8 range (slightly acidic), but there are exceptions. Alfalfa prefers a pH in the lower 7s. Blueberries and some oak trees thrive best in acidic soils below 6, for instance. Every plant has its own preferred range.
Lime is commonly used here to raise pH if the soil is getting acidic. Sulfur and several other products are used to lower pH. If lime is applied to mineral soils that have a high pH, say above 7.0 (basic soils), it can have a detrimental effect, because some plant nutrients are not as available at pHs of 7.0 or greater. Above 7.5, deficiencies like phosphorus, iron and manganese can show up in some circumstances. In most of these high pH solids need sulfur, not lime, because they need to have the pH lowered to more acidic levels.
You cannot look at the soil or the crop or the weeds growing in a spot and know how much lime or sulfur to add to bring the soil to the most favorable pH. The soil pH determination is done with a soil test. In most fields and gardens, it's good to take a soil test every two to three years, especially if you are adding a lot of manure, or compost or leaves or other organic matter. So the practice of applying 1,000 pounds of lime per acre annually is not based on any real knowledge, it's just a habit, maybe passed down from generation to generation.
In fact, here in northern Indiana, over the past 30 years, we have been seeing soil pHs changing, moving higher (less acidic) in many situations. We used to get sulfur from the steel mills to our west in the form of acid rain, but the anti-pollution technology has removed the sulfur from the smoke. Sulfur, of course, is both a plant nutrient and a way to lower pH. Farmers are seeing crop yields affected by this changing level of sulfur and pH, and many are now managing for this.
Again, remember that applying lime or sulfur does not instantaneously change the soil pH. It takes more than six months for the real effects to maximize. And, applying lime or sulfur over the top of an existing perennial crop, like alfalfa or turfgrass only changes pH in the top inch or so of soil, not 10-12 inches down where a lot of the roots are. For perennial plants like pastures, alfalfa and turf, the pH adjustment is best done six months before seeding.
The bottom line is: there are real scientifically valid reasons to apply lime and sulfur to lawns, gardens and fields, and that should be done with a soil test in hand. Spreading lime or sulfur because "it looks bad" or because "it is the way we always have done it" is not taking good care of your plants or soil.
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