What do you need?

Use the search below to search the site or find your local unit office.

Return to Skip Menu

Main Content

Trees and Shrubs for Acid Soils

ID

430-027

Authors as Published

Bonnie Appleton, Extension Specialist, Hampton Roads AREC; Robert Heins, Graduate Student, Hampton Roads AREC, Virginia Tech; Stephen Donohue, Crop and Soil Environmental Sciences; Gregory Eaton, Horticulture; Dawn Alleman, Norfolk VCE; Jim Williams, Hampton VCE, Virginia Tech

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?

Acid soils

Acid soils are all soils that test lower than pH 7.0, which includes most soils east of the Mississippi River. In reality, most of these soils do not have significant acidity problems. Soils with pH's below 6.0 may need special treatment or plant selection. When soils become very acid, however, with pH's below 4.5, problems develop for many common landscape trees and shrubs. These strongly acid soils need either amendment to raise the pH or careful plant selection.

    figure1a.jpg
    figure1b.jpg
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.

pH 

pH measures the available hydrogen ions in a solution, and describes the relative level of acidity or alkalinity measured on a scale of 1 (acid) to 14 (basic), with 7.0 as neutral. Vinegar is a mild acid; battery acid (sulfuric acid) is a strong acid. Baking soda is a mild base when mixed with water; lye (Drano) is a strong base. Pure water is neither basic nor acidic, and has a pH of 7.0.

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.

Causes of acid soils

Acid soils may be due to natural conditions or human disturbance of the soil. The same methods for adjusting acidity are recommended for either situation. The primary difference is that naturally acidic soil will eventually return to that state after pH adjustment, while pH adjustments to disturbed soils present a more long term change. Naturally acid soils occur when bedrock from which the soil evolved provides the natural elements for acidity, when rainfall leaches or washes away basic elements in the soil, or when land has been naturally forested. All of these situations are present in Virginia soils.

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
Strongly
acid
Medium acidSlightly acidVery slightly acidVery slightly alkalineSlightly alkalineMedium alkalineStrongly alkaline
4-5.55.5-66-6.56.5-77-7.57.5-88-8.58.5-10

Adjusting acid pH

Adding ground limestone, either calcium carbonate or calcium-magnesium carbonate (dolomitic lime) raises the pH of acid soils. Quicklime and slaked lime are also used and act faster, but are more expensive and disagreeable to use. The amount of limestone needed to change the pH of the top 8 inches of soil from 4.5 to a desired 6.5 varies according to soil type and ranges from approximately 150 lbs/1000 ft2 for a sandy soil to 250-300 lbs/1000 ft2 for a clay loam. The rate needed will be provided as part of the soil test results from a soil testing lab, if the soil type and the intended use of the land are listed when the soil sample is submitted.

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.

Trees and shrubs for acid soils

Many trees and shrubs that are tolerant of acid conditions (including strongly acid conditions below pH 4.5) are available for Virginia landscapes. These plants may often be a better solution than attempting to adjust the soil to a higher pH, particularly where the native soil condition is by nature acidic. For the following trees and shrubs, check their hardiness and heat zone tolerances relative to their suitability for your particular area. Note that most trees and shrubs native to Virginia are adapted to at least slightly acid soils.
pH 5.0 to 6.5 and above
TreesShrubs
Common NameLatin NameCommon NameLatin Name
Balsam and fraser firAbies balsamea and A. fraseriCarolina allspice*Calycanthus floridus
Maples* (Red)Acer speciesSummersweet*Clethra alnifolia
Serviceberry*Amelanchier arboreaScotch broomCytisus scoparius
Hinoki falsecypressChamaecyparis obtusaCleyera or ternstroemiaCleyera japonica
Fringetree*Chioanthus virginicusRedvein enkianthusEnkianthus campanulatus
China firCunninghamia lanceolataGardeniaGardenia jasminoides
Franklinia*Franklinia alatamahaWitchhazel*Hamamelis virginiana
Hollies* (Some)Ilex speciesBigleaf hydrangeaHydrangea macrophylla
LarchLarix deciduaHollies* (Some)Ilex species
Sweetgum*Liquidambar styracifluaAniseIllicium floridanum
Magnolias* (Some)Magnolia speciesVirginia sweetspire*Itea virginica
CrabapplesMalus speciesDrooping leucothoe*Leucothoe fontanesiana
Norway and Colorado sprucePicea abies and P. pungensMountain stewartia*Stewartia ovata
Longleaf pine*Pinus palustris  
Eastern white pine*Pinus strobus  
Scots or Scotch pinePinus sylvestris  
White and red oak*Quercus alba and Q. rubra  
Weeping willowSalix babylonica  
Sassafras*Sassafras albidum  
Mountain ashSorbus aucuparia  
Japanese stewartiaStewartia pseudocamellia  
Japanese snowbellStyrax japonica  
Canadian hemlock*Tsuga canadensis  
pH 5.0 and below
TreesShrubs
Common NameLatin NameCommonLatin Name
River birch*Betula nigraBottlebrush buckeye*Aesculus parviflora
Flowering dogwood*Cornus floridaHeaths and heathersErica species
Japanese dogwoodCornus kousaFothergilla*Fothergilla species
Japanese cedarCryptomeria japonicaJunipers*Juniperus communis and
American beech*Fagus grandifolia J. horizontalis
Carolina silverbell*Halesia carolinaMountain laurel*Kalmia latifolia
Black gum*Nyssa sylvaticaLoropetalumLoropetalum chinense
Sourwood*Oxydendrum arboreumJapanese pieris*Pieris japonica
Loblolly pine*Pinus taedaAzaleas andRhododendron species and
Virginia pine*Pinus virginianarhododendrons* (Some)hybrids
Golden larchPseudolarix kaempferiBlueberries, huckberries,Vaccinium species
Douglas firPseudotsuga menziesiietc.* (Some) 
Pin oak*Quercus palustris  
Willow oak*Quercus phellos  

*Native to Virginia

Rights


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.

Publisher

Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Jewel E. Hairston, Administrator, 1890 Extension Program, Virginia State, Petersburg.

Date

May 1, 2009