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Definition of Alkaline Soil

Updated on October 10, 2012
Zinnia elegans grows well in slightly alkaline soil.
Zinnia elegans grows well in slightly alkaline soil. | Source


On a scale of 0 to 14, pH is a measurement of the level of hydrogen ions in relationship to hydroxyl ions that exist within soil.

Alkaline Soil

Soil that is alkaline has a pH reading above 7.0.

Acidic Soil

Acidic soil measures below 7.0 on the pH scale.

Neutral Soil

Soil with a reading of 7.0 has neutral pH. Most plants prefer soil at or near neutral.

What is alkaline soil?

Alkaline soil, sometimes referred to as "sweet" soil, registers above 7.0 on the pH scale. Unlike acidic soil, which has a pH value of less than 7.0, alkaline soil contains more hydroxyl ions than hydrogen ions.

The Importance of pH

Soil pH is important because it affects the availability of nutrients in the soil. If soil is too alkaline or too acidic, many nutrients that plants require for optimum growth—or even survival—are not accessible to them.

The majority of plants grow best in relatively neutral soil that falls within a range of 6-7.5 pH, a little above or below 7.0. At these levels, the essential nutrients most plants need are most available to them. However, just as some plants prefer acidic soil, a number of plants grow best in soil that is a bit alkaline. (See the chart below.)

The Law of Tolerance

In ecology, the law of tolerance refers to a plant's ability to live in a broad range of pH values.

Plants with high tolerance may perform poorly in soil with pH values outside their preferred range, but they won't die.

Some plants, most notably weeds and other invasive types, have a very high tolerance for a wide range of pH levels (Foerster 17).

Slightly alkaline soil is just right for sunflowers, too.
Slightly alkaline soil is just right for sunflowers, too. | Source

What if soil is too alkaline?

To determine soil pH, run a soil test. If your soil is too alkaline to suit the plants you're growing, you can increase its acidity by adding organic matter. Over time, organic material, such as sphagnum peat moss, composted manure, leaf mold and other natural amendments, tends to bring soil pH values at or near neutral (7.0).

Although slow-acting, granular sulfur is an inexpensive amendment that will lower soil pH. Elemental sulfur, aluminum sulfate and iron sulfate will also decrease soil alkalinity (Everhart).

Trees, Vegetables, Flowers & Other Plants That Like Sweet Soil

Common Name
Scientific Name
Preferred pH Level
Abelia grandiflora
Asparagus officinalis
Canna spp.
Cherry (Sweet)
Prunus avium
Cotoneaster spp.
Ribes spp.
Dahlia variablis
Delphinium grandiflorum
Ulmus americana
Fern (Maidenhair)
Adiantum pedatum
Forsythia spp.
Hyacinthus candicans
Ivy (Boston)
Parthenocissus tricuspidata, var. veitchii
Lilac (Persian)
Syringa persica
Tilia spp.
Maple (Sugar)
Acer saccharum
Mentha arvensis
Hibiscus esculentus
Pachysandra (Japanese)
Pachysandra terminalis
Pea (Sweet)
Lathyrus odoratus
Carya illinoinensis
Paeonia albiflora
Poplar (Silver)
Populus alba
Poppy orientale
Spinacia oleracea
Helianthus augustifolius, H. annus
Viola canina
Violet (Blue)
Viola paplionacea
Walnut (Black)
Juglans nigra
Nasturtium aquaticum
Wisteria (Japanese)
Wisteria floribunda
Yucca spp.
Zinnia elegans

Works Cited

Everhart, Eldon. "How to Change Your Soil's pH." Horticulture & Home Pest News. Iowa State University Extension and Outreach. 6 April 1994. Web. 10 October 2012.

Foerster, John. "Ecology." Maryland Master Gardener Handbook. University of Maryland, 2008: 5-20. Print.

State Fair Zinnia
State Fair Zinnia | Source

About the Author

The Dirt Farmer has been an active gardener for over 30 years.

She first began gardening alongside her grandfather on her parents' farm. Together, they would plant acres of vegetable gardens, setting tomato, eggplant and bell pepper plants; sowing row after row of beans and corn; and building up mounds of soil for white squash, pumpkin, cantaloupe and potatoes.

Today, The Dirt Farmer gardens at home, volunteers at community gardens and continues to learn about gardening through the MD Master Gardener program.

Copyright © 2012 by The Dirt Farmer. All rights reserved.


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    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      7 years ago from United States

      Hi Derdriu. You have berry bushes? How wonderful! They do seem to love acidic soil. Nice to hear from you! Take care, Jill

    • profile image


      7 years ago

      Jill, Isn't it interesting that so many of the commonly cultivated and house plants tend to prefer soil whose pH is in the neutral range between acidic and alkaline?

      And then there are the trees such as the chestnuts, oaks and pines that act to acidify soil and the waters into which their soil may slip and slide! It's in those areas that my acidic pH-loving berry thickets thrive.

      Respectfully, and with many thanks for sharing, Derdriu

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      7 years ago from United States

      Hi Carol! Not the most exciting topic, but ... the info's good to know. Thanks for stopping by, Jill

    • carol7777 profile image

      carol stanley 

      7 years ago from Arizona

      I always knew that alkali is a good thing..eating as much alkali foods is best for our health. Learned a lot here as always . thanks for the great information. Voted UP and sharing.


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