An annual application of lime to turf / pasture grasses, orchards, vineyards, garden beds and agricultural soil is extremely beneficial to help maintain optimal soil pH. The acidity or alkalinity of soil is measured in a logarithmic scale referred to as pH. Maintaining a specific soil pH is critical to ensure optimal plant growth. The pH of ones soil will have a profound affect on the availability of nutrients. When soil pH is out of balance, either too high (alkaline) or more commonly too low (acidic), essential nutrients become tied-up within the soil resulting in nutrient deficiencies. A soil pH between 6.0 and 6.5 is ideal for most garden crops and will ensure nutrients are available to plants in soluble forms. Soil pH will also influence microorganisms within the soil that convert organic nitrogen from the ammonium form of nitrogen to the nitrate form that plants use.
A decrease in soil pH, know as soil acidification, is a natural process that is accelerated by crop production practices, especially the use of heavy tillage and nitrogen (N) based fertilizers. Acidic soil conditions can also result from the decomposition of organic acids found in plant liter, the leaching of nutrients (calcium, magnesium, potassium and sodium), and an accumulation of toxic elements such as aluminum and sulfur. Soils with low pH levels, below 5.0, contain higher levels of available aluminum and manganese that can become toxic to plants and may inhibit growth.
Testing your soil pH is helpful in determining the need for any pH adjustments specific to the types of crops you are cultivating. Extension offices throughout the country offer a variety of agricultural services including soil testing.Some state extension agencies offer soil testing for free or at discounted rates. The link below will help you locate your states extension offices and the services they provide. https://nifa.usda.gov/land-grant-colleges-and-universities-partner-website-directory?state=All&type=All. Soil samples tested thru state or private labs will provide the most accurate results and will also supply recommendations for fertilizers and liming agents. Simple pH testing devices are also available at garden centers and Internet retailers. Although not 100% accurate, home-testing devices will get you in the ballpark when testing soil pH.
Considered a soil conditioner, lime helps to neutralize acidic conditions and toxic elements, improve soil structure, support beneficial bacteria, and will improve the availability of soluble nutrients. In addition, lime provides calcium and an array of micro-nutrients not usually found in conventional fertilizers. Limestone is the most common material used to help neutralize soil conditions, although there are a few other types of materials that may also be used.
Garden Lime or Hi-Cal Lime is a 100% pure form of finely ground limestone composed of calcium carbonate (CaCO3). Garden lime is an abundant resource found throughout the world mined from the remains of ancient sea life.
Dolomite Lime (CaCO3 - MgCO3) is also sourced from natural deposits. In addition to containing a pure form of calcium carbonate, dolomitic lime also contains Magnesium in the form of Magnesium carbonate (MgCO3). Magnesium plays a key role in photosynthesis and is a building block of Chlorophyll.
Aragonite or Oyster Shell Flour is a high calcium material with a course texture much like sand. Aragonite Oyster Shell has a combined total of 97% calcium in the forms of calcium carbonate (CaCO3) and calcium silicate (Ca2SiO4) with very low levels of magnesium.
Wood Ash, especially when sourced from burnt hardwood trees (fireplace ash), can also be used in the place of limestone. Wood ash is primarily composed of calcium in the form of calcium carbonate (CaCO3). Wood ash also contains an array of nutrients beneficial to plant and soil health including; potassium, phosphorus, magnesium, iron, manganese and sodium in addition to trace amounts of boron, zinc, copper, molybdenum and many other micro-nutrients. If packaged as a commercial fertilizer, wood ash would be listed with an average N-P-K of 0-1-3 with a 30% Calcium content.
How Much Lime to Apply:
For best results have your soil tested to determine the soil texture and the current soil pH. The amount of liming materials needed to adjust your soil pH will vary based upon your soil texture and the current soil pH. For example it requires more lime to raise the pH of clay soil than it will to adjust sandy loam. Use the chart below to determine an initial application of lime. If a soil pH test is not available then half of the amount recommended below should be sufficient for annual pH maintenance.
How to Apply Lime:
When possible, lime should be worked into the top 6 inches of soil to ensure it is incorporated into the root zone of soil. This can be performed when soil is turned / tilled or after an aeration for lawns and turf grasses. For no-till gardener’s lime can be broadcast over the soil surface by hand or with a broadcast seeder. Keep in mind that lime moves very slowly in the soil and can take several years to move down a few inches.
When to Apply Lime
Lime can be applied at anytime of the year prior to planting crops. Lime is most effective when applied during the late autumn or early winter as limestone takes several months to properly react and correct soil acidity. Applying lime about 4 - 6 months in advance of seeding or transplanting your projected crops will ensure it has time to take effect. Lime can be applied to cold, frozen or dormant soils.Limestone should be broadcast evenly across the soil to ensure consistency. When planting fruiting trees and shrubs (other than acid loving crops which do not require lime) it is best to incorporate lime into the planting site and with the back-fill soil.
Further Reading:
Soil Acidity and Liming for Agriculture Soils
https://vric.ucdavis.edu/pdf/soil/ChangingpHinSoil.pdf
Sources:
https://content.ces.ncsu.edu/soil-acidity-and-liming-for-agricultural-soils
https://extension.psu.edu/can-you-apply-limestone-in-the-winter
https://www.agriland.ie/farming-news/five-benefits-of-having-the-correct-lime-content-in-your-soil/