If you want your plants to thrive instead of merely survive, you may want to check the chemistry of your soil. pH is a measure of alkalinity or acidity, on a scale of 0 to 14. The pH of soil affects the way plants absorb nutrients. A neutral pH is 7; most plants prefer a range of 6 to 7.5, although there are some plants, such as azaleas and blueberries, that like their soil on the acidic side. An alkaline pH of far greater than 7 may hinder the ability of plants to efficiently take up required macro- and micronutrients, while a very low or acidic pH can actually harm plants by making nutrients available faster and in greater amounts than the plant can process.
Testing your soil’s pH can be done with an inexpensive kit that you can purchase at most garden centers and hardware stores, or you can have it professionally checked by a laboratory for a fee. If you are taking your own samples, be sure to gather them from several different areas of your garden, as the soil chemistry may differ depending on the location.
Once you determine that your soil pH is an issue, you can make corrections by amending it. Bear in mind that significant changes are not usually possible — if your soil test yields numbers on the extreme ends of the pH scale, you may wish to reconsider where you are gardening! Modifying soil pH is not a quick and easy process: it will take several growing seasons and possibly more than one application to get the results you are looking for. If the site has good drainage, the task may be easier.
Regions with high precipitation and poor drainage typically exhibit acidic soils due to mineral leaching and pooling. If your garden soil is acidic, bring your pH number closer to neutral by adding an amendment such as agricultural lime. Agricultural lime is usually composed of a combination of minerals which include magnesium carbonate and calcium carbonate. (Lime containing iron or aluminum is also available if your soil requires those micronutrients). Dolomitic lime, which contains a large amount of magnesium carbonate, amends soil pH more slowly than calcitic lime, which is primarily composed of calcium carbonate. You can purchase limestone in an inexpensive pulverized form, but it is dusty to apply. A pelletized form is less messy, but costs more. Lime is also available in a highly concentrated hydrated form that can quickly change the pH. Overapplication can be a problem with hydrated lime, however — using too much can harm or kill your plants.
Alkaline soil may be a problem in arid climates and in soils with high clay content. The application of sulfur is commonly used to treat alkaline soils. Elemental sulfur in a granular form is often recommended as an acidifier for alkaline soils. It is a slow-acting amendment, however, and will require time to activate. It may be necessary to wait a year or more to plant your crops in the area of application. Iron sulfate works much more quickly but may need several applications depending on the area to be covered.
The amount of lime or sulfur required to amend your soil’s pH depends on the texture of your soil (the proportion of clay, sand, or loam particles) and how many increments on the pH scale you need to adjust for. Consult with your local university’s agricultural extension office for the necessary ratios for proper coverage. Always follow all label instructions when applying chemicals, and wear protective clothing. Broadcast the amendment over the soil with a drop spreader, then thoroughly incorporate it into the upper soil layers, to a depth of at least six inches. If you do not wish to disturb the soil by tilling, lime or sulfur can also left on the surface of the soil, but it will take longer for the amendments to activate the necessary chemical changes.