Tag Archives: soil pH


By   October 12, 2015

For most US lawns, the most beneficial additive that can be applied isn’t fertilizer, it’s lime. Most homeowners know that it’s needed, but few know the importance of when, why, and how much.

Global variation in soil pH.

Global variation in soil pH. Red = acidic soil. Yellow = neutral soil. Blue = alkaline soil. Black = no data. Chart by Ninjatacoshell (Own work) [CC BY-SA 3.0 or GFDL], via Wikimedia Commons

As you can see from the chart, just about all of the regions in the US where grass is commonly grown are natively acidic.  The blue areas are mostly arid desert and we can’t use the term “easy lawns” there.

Lime is applied to the soil to increase the soil pH. pH, a measure of the soil’s acidity or alkalinity, and can directly influence the vigor and quality of the home lawn. When the pH is below 7.0, the soil is said to be acidic; when above 7.0, it is alkaline.

When the pH drops below 6.0, the chemical reactions that supply some of the lawn’s nutrients can’t happen. It’s a form of malnutrition, the food might be there, but your lawn just can’t use it. Low pH limits your lawn’s ability to use nitrogen, phosphorus, potassium, sulfur, calcium, magnesium and molybdenum is restricted. The result is that your good looking fine grass’ growth is stunted and less desirable varieties or weeds or moss are able to take over.

Overly high pH can be just as bad. Alkali soil over pH 8.0 limits your lawns ability to use nitrogen, phosphorus, iron, manganese, boron, copper and zinc. Either way, too high or too low, and your lawn will start to show a loss of color, vigor, and tolerance for drought, heat, and stress.

Most soils tend to be acidic. Heavy rainfall and long time cultivation, combined with the type of soils left behind by the ice age, tend to leach the neutralizing minerals out of the ground. Of course, acid rain doesn’t help, and decomposing leaves add to the acid levels.

Fortunately, acidic soil is easy and moderately inexpensive to fix. Limestone is  very common and it acts just like a giant Tums tablet when it’s applied to your law. It neutralizes acid and provides calcium and trace minerals at the same time.

Before you start, a soil test can tell you how much you will need. Don’t be surprised, it’s going to seem like a lot, but lime is inexpensive and, aside from carrying it home, it goes on easily. Your test will indicate how many pounds of pure calcium carbonate you will need per 1000 square feet. Since different types of limestone have slightly different contents, you’ll have to do a simple calculation. Use the table at the bottom of the page to determine how much you will need.

Lime can go on any time of the year when the ground isn’t frozen or the grass isn’t parched or wilted. It’s a good idea to water after application to wash it off the grass blades and before it blows away.


Lime Materials And Their Characteristics 

Material Calcium carbonate equivalent Rate of pH change Max. recommended rate of application Other comments
Burned Lime 180 Fast 10 Hazardous, difficult to apply
Dolomitic Limestone 70-95 Slow 50 Also a source of magnesium
Ground limestone 70-95 Slow 50
Hydrated Lime 140 Fast 20 Hazardous, difficult to apply
Pelletized Limestone 70-95 Fast 50 Easy to apply, more expensive than other sources

All values are approximate and vary by product.

Soil Ph

By   October 8, 2015

Inexpensive soil testing kits are available at most garden shops and state agricultural extension offices. Theoretically, they can tell you exactly how much of each nutrient that you need to add and when to add it.

Even without a test, I can tell you with 95% certainty what you need here in the Northeast. Since Nitrogen is water soluble and gets consumed quickly in a lawn, chances are very high that unless you have fertilized in the last few weeks, your lawn needs lots of Nitrogen. Phosphate and Potassium don’t get used up as quickly, but established lawns have usually used up most of the supply.

Ph is Important

The test that is important, though, is pH. Here’s where you get to throw around technical terms and act like a scientist. pH is an abbreviation for the potential of hydrogen, or simply a measurement of the amount of acidity or alkalinity in a substance. It’s important because everything that goes on inside the cells of grass plants is chemistry based, and some chemicals just don’t work right if things don’t have the right amount of acid.

Without getting too technical, pH is measured from 0 to 14, with 0 being the ultimate alkaline level, 14 is the strongest acid, and neutral is in the middle at 7. Not surprisingly, grass likes it best around soil Ph of 7.

Here in New England, our combination of soil type, water, and our types of trees make everything acid. Fortunately, there’s an easy and inexpensive way to fix your soil’s pH. It’s the equivalent of giving your lawn a big Tums…ground up Limestone is available from most garden shops and discount stores. It goes on easily, starts working quickly, and lasts a long time.

The bad news is that it sometimes takes a lot of limestone to correct neglected soil, it may take a while to penetrate down to the lower levels of your lawn’s roots, and needs to be reapplied every few years.

Limestone is generally available in two forms, ground to a powder and pelletized. The ground limestone is the least expensive and, up until a few years ago, was the most popular. It’s a fine powder and needs to be applied with a drop-type spreader. Many a gardener has found that, as they work up a sweat pushing the spreader, the fine powder that blows around sticks to their moist skin and they end up looking something like Casper the ghost.

Pelletized limestone eliminates this problem. It’s formed into small pellets that spread easier, don’t blow around, and can be applied much quicker with a broadcast spreader.

An important note…limestone is generally safe. After all, it’s added to food as a source of calcium, but it’s never good to expose your skin to large amounts of the low pH material, and getting the dust in your eyes or nose can cause irritation.

High Ph

It’s unusual but some in some locations the soil might be too alkaline, the opposite problem that most of us face.  It’s unusual in the major grass growing zones, so if you soil tests as heavily alkaline retest to be sure.  Some plants and shrubs like their Ph to be heavily acid.  Blueberries are the most common acid lovers although many of the evergreen foundation plants will prefer slight acid.  Hydrangeas will tell you if they need more acid.  Above Ph 5.5 soil Ph or so and their flowers will be pink, below 5.5 and the flowers are blue. Aluminum sulfate is the most common chemical used to bring the Soil Ph down.


By   October 8, 2015

Moss is a common problem and is frequently blamed on low pH, but this is only part of the problem. Even though mosses are often found on soils with low pH values, they may also become established in areas of low fertility, shade, improper drainage, and/or packed soil. Often, two or more of these factors combine to create conditions unsuitable for vigorous turf growth.

A soil test will determine the pH and fertility level of the soil and recommend the necessary lime and fertilizer. The other factors can be determined by visual inspection.

Moss growing in a lawn

Moss growing in a lawn

Site conditions need to be addressed to eliminate the moss completely. Compacted soils can be loosened manually or mechanically, and poor drainage may sometimes be improved by minor regrading.

Trees can reduce the amount and quality of light your lawn area receives, and tree roots compete with the lawn for water and nutrients. Where the tree cover isn’t especially dense, removal of a few carefully selected lower branches may improve light conditions enough for moderate grass growth. Another option is mulching or growing plants more suitable to the site or planting a shade tolerant type of grass. There are many types of ground cover that will thrive where grass has a tough time.

Once the pH and other conditions are resolved, the moss needs to be physically removed before reseeding. It should come up easily with a rake as the moss does not have deep roots or anchors. Grass won’t grow unless the seed can make physical contact with the soil. There are some commercial moss killers on the market that contain ferrous sulfate or ferrous ammonium sulfate, but they’re not always useful and they can stain concrete walks or patios. Sometimes it’s easier to just skip the killer and rake it off.  Conditions still need to be improved or moss will return, and the moss killers leave behind dead moss which still needs to be removed.

On the flipside, moss transplants easily and can make a great groundcover in rock gardens or out of the way places.  It doesn’t stand up well to traffic and isn’t good for walkways.