Lime in Gardens
Nearly every homeowner wonders about whether or not to use lime in their garden and on the lawn. However, few probably have a complete understanding of why liming can be an important aspect of a home garden care program, how to determine if liming is needed, and how one should go about applying lime.
To understand the role of lime in the garden, it is necessary to understand soil conditions. Most soil in Rhode Island is acidic and will benefit from lime. However, the only way to determine how much lime to apply is through the results of a soil test. A soil test kit or pH probe used to test soil pH may indicate the need for liming but this simple test does not allow one to determine how much lime is needed to correct the acidic condition.The amount of lime for a particular soil is designated as the lime requirement on soiltest reports obtained from soil testing laboratories.
pH and Lime
Soil pH, a measure of the soil's acidity or alkalinity, can directly influence the vigor and quality of plants, vegetables, and lawns. When the pH is below 7.0, the soil is said to be acidic; when above 7.0, it is alkaline. Lime is applied to the soil to increase soil pH.
Several factors cause the formation of acidic soil conditions. One primary cause is the leaching of base nutrients such as calcium, magnesium, and potassium from the soil. This occurs more frequently in areas of heavy rainfall or heavy irrigation. A second causeis the use of acidifying nitrogen fertilizers. However, the extent to which fertilizer application will affect soil pH is dependent on a number of factors, including: type of nitrogen applied, amount applied, types of other nutrients present in the fertilizer, soil type, andirrigation frequency. Other factors which may act to reduce soil pH are decomposition of soil organic matter and irrigation with acidic water.
Soil that is between about 6.0 and 7.5 has some real advantages for plants. Higher levels of nutrients are available to be accessed by roots. Plants need mineral elements like nitrogen, phosphorous, and potassium, which are used in larger amounts than other minerals and are called "primary nutrients." Next in importance are calcium,magnesium, and sulfur. Trace elements like copper, zinc, and iron are also needed. In general, the pH levels between 6.0 and 7.5 provide the broadest availability of nutrients.
If the pH gets too high or too low, nutrient availability drops. Soil microbes are also active at these pH levels. These microbes contribute to plant health by digesting nutrients and converting them into forms that can be taken up by root cells. Over-application of liming products may cause the development of alkaline (high pH) soil conditions.
Landscape Trees and Shrubs
If the landscape consists mainly of shrubs and trees that are growing satisfactorily, there may be no concern necessary about liming soil. Many of the tree and shrub plants in Rhode Island, such as conifers, rhododendrons, azaleas, heather, and andromeda must have acid soils to thrive best. Thus, they grow well without additional lime.
Lawns
No lime may be needed on the lawn either, but if lime is needed late fall is a good time to lime soil because common amendments like dolomite limes take three to four months to break down. Turf grasses prefer pH between 5.5 and 7.0. Mid October is time for the last application of fertilizer to the lawn. When installing a new lawn, get a soil test done to establish the pH level and add lime before planting if necessary, that is, if the soil pH is below about 5.5. Do not apply lime and fertilizer at the same time. Lime should go on first; wait at least 30 days after applying lime before fertilizing.
Vegetable Gardens
Vegetables produce the best crops at soil pH between 6.0 and 7.0. The exact amount of lime to add depends on the pH of the soil. Dolomite lime is most often used because it supplies magnesium as well as calcium. Add lime in late fall after crops are harvested to prepare soil for planting the following spring.
Adapted from: Ohio State University Extension, 2000; Washington State University, 1998
Useful Website
What Does Lime Do in the Garden? (Washington State University Extension)
