Sometimes it seems that there is so much to understand when dealing with the garden and landscape that it can be overwhelming. You finally figure out all that stuff about hardiness, mulching, pruning and fertilizing and then they throw in pH. It really is important. But don't despair… it isn't all that complicated. You just need to be aware that pH is a factor that can influence your gardening and learn the indicators of a pH problem. Since you have much more important things to keep in your head than how much lime per 1000 square feet or whether it is better to use elemental sulfur or aluminum sulfate, you just need to know where to find the answers!

Just what is pH and why is it important? pH is a measurement of acidity or alkalinity in soil. Your soil pH influences whether or not plants can make use of available nutrients.

How can I measure the pH in my soil? Soil can be tested by the University of Minnesota or many other independent soil testing labs. There are also several easy-to-use home pH tests available that will give you a general measurement. Most home tests involve putting a pinch of reactive agent and a pinch of soil into a little test tube that you fill with water and shake. Match the color of the water with a color scale that is provided to determine your pH. Since water also has a pH, it can influence the outcome of your test. To increase the accuracy of home tests, just use distilled water instead of tap water.

What do the different readings mean? PH is measured on a scale of 0 to 14. A pH of 7.0 is considered neutral. All readings with a number value higher than 7.0 are considered alkaline. 7.0-8.0 is slightly alkaline and 8.0 to 9.0 is moderately alkaline. Readings with number value lower than 7.0 are considered acid. 6.0 to 7.0 is slightly acid and 5.0 to 6.0 is moderately acid.

Will the pH vary much in different locations in my yard? It can vary significantly. If you suspect that might be the case take several soil samples and use a home test.

Once I have my soil tested, do I need to do it again? It's a good idea to test your soil each season, especially if your plants are showing symptoms that might indicate a problem. While pH doesn't change very quickly, several factors can change the pH in your soil over a season. For instance, city water in much of our area has a pH of 7.5-8.5 and watering with it gradually makes your soil more alkaline. Similarly, some soil amendments will acidify your soil as they break down.

What kind of symptoms will my plants have if the pH is not what they like? Since pH can make nutrients in the soil unavailable, plants will look like they need fertilizing, the leaves yellowing mid-season and not responding to fertilizer.

What pH do most plants like? The vast majority of plants grow well with a pH from 6.0 to 7.0. When you find out a specific plant prefers a pH of 6.5, keep in mind that most plants are tolerant of a fairly wide range and that value of 6.5 represents the middle of the range. Only a few require a specific pH.

What is the difference between tolerating and requiring a certain pH in the soil? Tolerance means the plant will not show a significant difference when the pH isn't what is ideal. For instance, delphiniums do best in a slightly alkaline soil, but will grow in neutral or slightly acid pH. A few plants require a certain pH and simply won't thrive without it. Azaleas and blueberries require very acid soil.

Are there plants that actually like it acid? Almost all garden plants prefer a slightly acid pH. If your pH is moderately acid, try growing Azaleas, Rhododendrons, Clethra, Holly, Foxglove, Trillium, Bleeding Heart and Bluebells.

Is there anything that does well where the soil is alkaline? For alkaline soil you don't want to adjust, try delphiniums, dianthus, boxwoods and spirea. Many salt tolerant plants grow in moderate alkalinity.

How can I adjust pH? To change the soil pH, you need to take into consideration the type of soil and what you want to use to change the pH. Sandy soils are easier to acidify than clay soils. To make acid soil less acid, you need to add alkaline materials such as lime. To make soil more acid, you need to add acid materials such as peat moss, sulfur, iron sulfate or aluminum sulfate. (Use of aluminum sulfate is associated with damaged plant roots and heavy metal contamination of the soil.)

How do I choose which material to use when changing pH? Consider cost, how quickly the material will work and how you want to apply it. Most materials used for changing pH are organic, but not all. Sulfur is usually the least expensive way to acidify soil. Lime is the least expensive way to make soil less acid. University soil test results will recommend the right materials and amounts for your situation.

The garden center sells different types of lime. What is the difference? Most lime is ground limestone, either calcitic lime (calcium carbonate) or dolomitic lime (calcium-magnesium carbonate). The type of lime available at local garden centers usually depends on what is found naturally in the area. Dolomitic lime is best in soils low in magnesium, but calcitic lime is usually less expensive. All lime is very slow to break down and won't affect your pH for months. You may also find hydrated (or quick) lime. It is more alkaline than ground limestone so it takes less to change the pH, but it is a fine powder that is harder to work with and you'll need to be especially careful not to let the caustic powder get into your eyes, nose and mouth or on your skin.

What are the differences between pelleted, granulated and powdered lime? To make lime easier to spread and quicker to dissolve, lime can be ground very fine and then made into pellets. Granular lime usually flows through a spreader fairly well, but is much slower to dissolve. Powdered lime is quick to dissolve, but can be very difficult to spread.

Is gypsum different from lime? Gypsum is calcium sulphate and can be applied to alkaline soils to move the pH toward neutral. It is sometimes recommended for clay soils.

Is there a best way to apply these products? Is there a best time? To determine how much to use and how best to apply it, check the instructions on the package. If you have your soil tested by a soil laboratory, it may provide you with specific recommendations.

Can I bring my soil test results in and get some help? We'd be glad to help you. If our horticulturist isn't available when you stop by, just leave the information and we will get back to you as soon as possible.

Additional Bachman's Information
Acidifying Soils
Understanding Your Soil
Soil Tests
Working With Clay Soils

Recommended Products
Pelleted and Hydrated Lime
Baled Peat Moss
Elemental Sulfur and Aluminum Sulfate