You can buy the best fertilizer on the shelf, water perfectly, and mow at the right height. But if your soil pH is off, none of it works the way it should. Soil pH is the invisible factor that controls how well your lawn, trees, and shrubs absorb nutrients. And most homeowners have no idea what theirs is.
What Is Soil pH?
Soil pH measures how acidic or alkaline your soil is on a scale from 0 to 14. A pH of 7.0 is neutral. Below 7 is acidic. Above 7 is alkaline.
Most plants, including the cool-season grasses common in northeast Indiana, prefer soil between 6.0 and 7.0. In this range, the nutrients in the soil are most available to plant roots. Step outside that range and nutrients start getting locked up in chemical forms that plants cannot absorb, even though the nutrients are technically still in the soil.
Purdue Extension explains it this way: soil pH acts like a gatekeeper. When pH is in the right range, the gate is open and nutrients flow freely to the roots. When pH is too high or too low, the gate closes and the plant starves even in nutrient-rich soil.
What pH Does to Nutrient Availability
This is where it gets practical. Here is what happens at different pH levels:
Below 6.0 (too acidic): Nitrogen, phosphorus, and potassium become less available. Aluminum and manganese can reach toxic levels. Grass thins out, turns yellowish, and struggles to grow even with regular fertilizing.
6.0 to 7.0 (ideal range): All major nutrients are readily available. Beneficial soil bacteria are most active in this range, which helps break down organic matter and recycle nutrients naturally.
Above 7.5 (too alkaline): Iron, manganese, and zinc become less available. You may see yellow leaves with green veins, a condition called iron chlorosis. This is common in trees like pin oaks and river birch when planted in alkaline soil. Ohio State Extension identifies iron chlorosis as one of the most common tree problems in the Midwest, and it is almost always a pH issue, not a fertilizer issue.
What Causes pH Problems in NE Indiana?
Several factors can push your soil pH out of the ideal range. Some are natural and some are caused by things around your property.
Native soil composition. Much of the soil in the Fort Wayne and Marion area is derived from glacial deposits with varying amounts of limestone. Some spots naturally lean alkaline, while low-lying areas with more organic matter tend to be more acidic. Purdue Extension's Indiana soil maps show significant variation even within a single neighborhood.
Concrete and masonry leaching. The area within a few feet of foundations, driveways, and sidewalks often has higher pH because calcium leaches out of the concrete over time. This is a common cause of yellow, struggling grass right next to a house foundation.
Repeated fertilization. Some nitrogen fertilizers, particularly ammonium-based products, gradually lower soil pH over time. Purdue Extension notes that lawns treated with ammonium sulfate or ammonium nitrate for many years may develop increasingly acidic conditions.
Irrigation water. If you are on well water, the mineral content of your water can shift soil pH over time. Hard water (high in calcium and magnesium) tends to raise pH. Soft water can lower it.
How to Test Your Soil pH
The most reliable method is a lab test through Purdue Extension. Collect soil samples from several spots in your yard (6 to 8 cores from a consistent depth of about 4 inches), mix them together in a clean bucket, and send about a cup of the mixed sample to the lab. Instructions and sample bags are available at your local Extension office.
The Purdue soil test costs around $15 and gives you pH, phosphorus, potassium, and organic matter content plus specific recommendations for your soil. This is far more accurate than home test kits, which can be off by a full point or more.
Ohio State Extension recommends testing every three to four years, or sooner if you are having unexplained problems with your lawn or landscape.
How to Raise pH (Too Acidic)
If your soil test shows pH below 6.0, you need lime. Lime is ground limestone (calcium carbonate) and it neutralizes acidity over time.
Purdue Extension provides specific lime application rates based on your soil test results and soil type. Clay soils need more lime than sandy soils to achieve the same pH change because clay has more buffering capacity. A typical recommendation might be 40 to 50 pounds of pelletized lime per 1,000 square feet, but follow your soil test recommendation rather than guessing.
Lime takes time to work. You will not see results for two to three months, and the full effect may take six months to a year. Fall is the best time to apply lime because winter rain and freeze-thaw cycles help it work into the soil. Iowa State Extension confirms that fall lime applications are more effective than spring ones.
How to Lower pH (Too Alkaline)
If your soil is above 7.5, elemental sulfur is the standard amendment. Soil bacteria convert the sulfur to sulfuric acid, which lowers pH. Like lime, this is a slow process that takes months.
Purdue Extension provides sulfur application rates based on your target pH and soil type. Be careful with sulfur — applying too much at once can damage plants. It is better to make smaller applications over two or three seasons than to try to fix everything at once.
For trees with iron chlorosis caused by high pH (like pin oaks), soil sulfur applications can help but take a long time. Ohio State Extension notes that foliar iron sprays or trunk injections provide faster relief for symptomatic trees while you work on correcting the soil pH underneath.
pH and Your Trees
Soil pH matters for trees too, not just lawns. Many common landscape trees in northeast Indiana have specific pH preferences:
Pin oak and river birch: Prefer acidic soil (pH 5.0 to 6.5). These trees are very prone to iron chlorosis in alkaline soil. If you are planting one, test your soil first. Purdue Extension specifically warns against planting pin oaks in high-pH sites.
Sugar maple and honeylocust: Tolerant of a wide pH range (5.5 to 7.5). These are good choices for northeast Indiana because they handle our variable soils well.
Arborvitae and yews: Prefer slightly acidic to neutral soil (6.0 to 7.0). They struggle in very alkaline conditions.
The Bottom Line
If your lawn or landscape is not responding to fertilizer, watering, and good care, the answer is probably underground. A $15 soil test can reveal a pH problem that, once corrected, makes everything else work better. It is the single most underused tool in home lawn care.