Raising pH is easier than lowering it. And though there are other alternatives, amending your garden soil with limestone is probably the best method of achieving a pH increase.
Coarsely ground limestone is easier to apply than powdery pulverized limestone.
But pulverized limestone will lower the pH more rapidly.
Another alternative is to buy granular limestone (sometimes called prilled limestone).
This type of limestone is made by mixing finely ground limestone with clay. The resulting pellets are very easy to apply by hand or with a fertilizer spreader.
As the clay pellets become moist, the limestone separates from it and begins to do its job of raising pH levels.
There are two types of limestone to choose from in raising the pH of acidic soil – calcitic limestone and dolomitic limestone.
Which one should you use?
Both will work to increase pH. But if your soil happens to be low in magnesium, choose dolomitic limestone, since it will also add some magnesium to your soil. Both will also increase the calcium level of your soil.
Whichever type of limestone you choose, be sure to work it thoroughly into the top 6 inches of your soil.
The amount of limestone to apply varies depending upon the amount of pH increase needed and the texture of your soil. The greater the amount of clay in your soil, the more resistant it will be to moving the pH up. On the other hand, changing soil pH is much easier in sandy soils.
Wood ash may be used as an alternative to limestone. Wood ash works much quicker than lime, but the pH change won’t be as great or as long lasting as with lime. Wood ash will also add some valuable nutrients to your soil such as potassium.
It’s recommended that you apply no more than 20 pounds of ash per 1000 square feet.
And you probably shouldn’t add wood ash to soil in which you plan to grow potatoes. Wood ash will increase the possibility of your potatoes becoming infected with potato scab.
Be careful, too, not to mix wood ash with nitrogen fertilizers like ammonium nitrate, ammonium sulfate and urea because the combination will generate ammonia gas.
Changing soil pH can be a long term project.
Depending upon how much you need to raise the pH, it might take several months after applying lime to achieve your goal. So it’s best to plan ahead.
And though you can easily test your garden soil pH yourself, it’s best to have your soil tested initially by a soil testing lab. They’ll give you specific recommendations about the amount of lime to use for changing your soil pH.