The trees and shrubs on your new home site are growing poorly, so you take samples to the Extension office and the agent suggests a soil test. Test results show that your soil has a pH of 4.5, which is rated as strongly acid. The agent suggests you either take corrective action to raise the pH or grow different plants.
What do the test results mean? What are "acid soils" and what does pH measure? Why does this matter to your plants? How can you correct the situation or what alternative trees and shrubs can you grow?
|Interveinal chlorosis often develops when soil pH, that is either too high or too low for a particular plant, makes an important nutrient unavailable for plant absorption.|
The pH scale is logarithmic, with 14 gradations. Each increment of 1.0 actually represents a difference of ten times either more basic (alkaline) or acidic (i.e., 6.0 is ten times more acid than 7.0, 5.0 is a hundred times more acid than 7.0, and 4.0 is a thousand times more acid than 7.0). Acid soils are often called "sour" soils and basic soils are often called "sweet" soils.
Soil nutrients are available to plants for uptake and use only when they are dissolved in water as ions. Nutrient availability differs depending on the pH of the soil solution. A soil pH range of 6.0 to 7.0 provides the greatest compromise of nutrient availability for plants. Moving away from the pH 6.0 to 7.0 range makes some nutrients more available, while decreasing the availability of others. A decreasing or more acid pH not only makes some nutrients less available, but it may also cause others, such as Al and Mn, to become available in toxic concentrations.
Virginia soil pH's range from 4.0 to 8.0 with most in the 5.1 to 5.5 range. Virginia rainfall is high, averaging 40 to 45 inches per year. Over time this rainfall has carried away water-soluble basic elements (i.e., Ca, Mg, K, NA), thus resulting in acid soils. High rainfall has also supported Virginia's forests. In contrast, low rainfall tends to produce natural grasslands with minimal leaching and thus alkaline (basic) soils.
Manmade acidic soils occur as a result of mining operations, farming, construction site development, and similar events that remove topsoil and expose the naturally acidic subsoil, or that deplete the soil of basic-forming elements. What is left is usually lacking in organic matter and available nutrients. While pH recovery can occur naturally, it will be slow, as will be plant reestablishment.
Landscape fertilization practices can also affect soil acidity. Repeated use of high ammonium or urea fertilizers, especially to turf areas that cover tree roots, can compound acidity problems. In situations where the soil is too acid, it may be better to use more basic fertilizers, many of which are nitrate based. Water used for landscape irrigation can also contribute to acidity problems and, therefore, it is valuable to have both your soil and your water tested before taking corrective measures.
|Soil pH categories|
|Medium acid||Slightly acid||Very slightly acid||Very slightly alkaline||Slightly alkaline||Medium alkaline||Strongly alkaline|
Ideally, lime should be worked into the soil to a depth of at least 8 inches. This is possible when preparing a new site with bare ground. Lime incorporation can be combined with deep tilling and the addition of organic matter (compost/manures) and fertilizer to revitalize a site that has been stripped or over-farmed. Lime incorporated into the soil will increase the pH to the target level (i.e., 6.5) in about two years.
Raising the pH of an established landscape, however, is much harder because incorporating lime into the soil may damage existing plant roots. If the total quantity of lime recommended exceeds 50 lbs/1000 ft2, split surface applications into a series of several smaller applications over time. Unfortunately, surface applications take longer to significantly change the pH below a 4 inch depth. Adding lime to the surface without incorporating it is not a desirable method for correcting acidity deep in the soil.
|Common Name||Latin Name||Common Name||Latin Name|
|Balsam and fraser fir||Abies balsamea and A. fraseri||Carolina allspice*||Calycanthus floridus|
|Maples* (Red)||Acer species||Summersweet*||Clethra alnifolia|
|Serviceberry*||Amelanchier arborea||Scotch broom||Cytisus scoparius|
|Hinoki falsecypress||Chamaecyparis obtusa||Cleyera or ternstroemia||Cleyera japonica|
|Fringetree*||Chioanthus virginicus||Redvein enkianthus||Enkianthus campanulatus|
|China fir||Cunninghamia lanceolata||Gardenia||Gardenia jasminoides|
|Franklinia*||Franklinia alatamaha||Witchhazel*||Hamamelis virginiana|
|Hollies* (Some)||Ilex species||Bigleaf hydrangea||Hydrangea macrophylla|
|Larch||Larix decidua||Hollies* (Some)||Ilex species|
|Sweetgum*||Liquidambar styraciflua||Anise||Illicium floridanum|
|Magnolias* (Some)||Magnolia species||Virginia sweetspire*||Itea virginica|
|Crabapples||Malus species||Drooping leucothoe*||Leucothoe fontanesiana|
|Norway and Colorado spruce||Picea abies and P. pungens||Mountain stewartia*||Stewartia ovata|
|Longleaf pine*||Pinus palustris|
|Eastern white pine*||Pinus strobus|
|Scots or Scotch pine||Pinus sylvestris|
|White and red oak*||Quercus alba and Q. rubra|
|Weeping willow||Salix babylonica|
|Mountain ash||Sorbus aucuparia|
|Japanese stewartia||Stewartia pseudocamellia|
|Japanese snowbell||Styrax japonica|
|Canadian hemlock*||Tsuga canadensis|
|Common Name||Latin Name||Common||Latin Name|
|River birch*||Betula nigra||Bottlebrush buckeye*||Aesculus parviflora|
|Flowering dogwood*||Cornus florida||Heaths and heathers||Erica species|
|Japanese dogwood||Cornus kousa||Fothergilla*||Fothergilla species|
|Japanese cedar||Cryptomeria japonica||Junipers*||Juniperus communis and|
|American beech*||Fagus grandifolia||J. horizontalis|
|Carolina silverbell*||Halesia carolina||Mountain laurel*||Kalmia latifolia|
|Black gum*||Nyssa sylvatica||Loropetalum||Loropetalum chinense|
|Sourwood*||Oxydendrum arboreum||Japanese pieris*||Pieris japonica|
|Loblolly pine*||Pinus taeda||Azaleas and||Rhododendron species and|
|Virginia pine*||Pinus virginiana||rhododendrons* (Some)||hybrids|
|Golden larch||Pseudolarix kaempferi||Blueberries, huckberries,||Vaccinium species|
|Douglas fir||Pseudotsuga menziesii||etc.* (Some)|
|Pin oak*||Quercus palustris|
|Willow oak*||Quercus phellos|
*Native to Virginia
Virginia Cooperative Extension materials are available for public use, re-print, or citation without further permission, provided the use includes credit to the author and to Virginia Cooperative Extension, Virginia Tech, and Virginia State University.
Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Alan L. Grant, Dean, College of Agriculture and Life Sciences; Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Jewel E. Hairston, Administrator, 1890 Extension Program, Virginia State, Petersburg.
May 1, 2009