Soil pH – Guide to Acidic Soil and Alkaline Soil Adjustment


soil ph testPreviously, we had a brief overview of soil pH, the component in organic soil that defines the chemistry of the soil in your garden.

In this post, we’re going to dig deeper into soil pH—how to check if you’re working in an acidic or alkaline environment, and how to improve soil if an extreme soil chemistry exists in your garden.

What is Soil pH?

Soil pH is simply the chemical characteristic of the soil—its level of acidity or alkalinity measured by pH. The soil pH scale runs from 1 for pure acid to 14 for pure alkaline, with 7 as the neutral midpoint.

Although typical garden soil pH never hit the extremes, slight movements up and down the pH scale can affect the health and hardiness of your plants.

Extremely alkaline soils with soil pH running above 7.5 and extremely acidic soils with soil pH below 5.0 tend to stunt plant growth because plants can’t take up nutrients effectively within these ranges. Highly acidic environments leach off plant nutrients while highly alkaline soil locks up nutrients in the soil.

Luckily though, soil pH in typical gardens comfortably range between 4.0 and 8.0, and most plants thrive within the 5.5 to 7.5 pH range so adjusting for beneficial soil chemistry would only need raising or lowering pH by a point.

Testing for Soil pH

For a successful growing and gardening experience especially when you’re starting a new garden, checking up on soil pH is usually the first step. You can do this in two ways:

Using a soil test kit which you can purchase from any garden center, or
Sending a soil sample to a laboratory or your local extension center for a soil analysis.

If you decide to do a spot of soil pH testing at home with a soil test kit, make sure that you use soil taken from a depth of 4 inches. Crumble about a tablespoonful of soil and mix with the reagent in a test tube, wait for the color to change, and then compare with the chart that comes with the kit to determine soil pH.

When you’re itching to start your garden right away, here’s the quick and easy way:

  • For acidic soil: Baking soda mixed with wet soil sample will froth.
  • For alkaline soil: A few drops of cider vinegar on a soil sample will fizz.

tomatoesAcidic Soil

The soil pH in natural forests tend to range from light to extremely acidic soils, mainly due to the decomposition of leaves, pine needles and dead trees which are typically acidic. If your area also frequently receives high rainfall levels, chances are the soil may be slightly acidic as the natural leaching action of rain encourages acidity in soil.

To lower soil acidity to the soil pH range that most plants normally need, add lime, organic matter or mulches. One quick solution is to occasionally spray soil with a mild solution of 1 tablespoon baking soda mixed in 2 liters of water. This will reduce soil acidity towards a more neutral or comfortably acidic soil pH range.

You can also apply dolomic limestone in tiny doses if soil acidity is below 6.0 to help plants absorb nutrients. Be careful to apply lime over time and in small doses. Too much too soon burns plant roots and is toxic to beneficial soil life.

Although you can add lime during any season, the best time to apply lime is in autumn because it needs about two to three months to settle and stabilize to start working. If you apply lime in the fall, highly acidic soil would’ve been treated and ready by spring.

The quickest way to get plants thriving in acidic soils is to grow plants that love this kind of soil. To list a few:

  • Trees, shrubs and bushes: Balsam fir, china fir, larch, magnolia, crabapple, gardenia, anise, Norway spruce, Japanese snowbell, weeping willow
  • Vegetables: Tomatoes, carrots, beans, peas, peppers, Irish potatoes
  • Fruits: Blueberries, cranberries, strawberries, apples, pears, bananas
  • Flowers: Golden lights azalea, amelia chrysanthemum, autumn blush coreopsis, Echinacea, blue haze euphorbia, ferns, hosta

okraAlkaline Soil

In contrast to acidic soils, alkaline soils are native to areas where the climate is mostly dry and warm. The low level of rainfall that these areas receive doesn’t rinse off, dissolve or evaporate the salts and chemicals that usually build up in the soil.

Because organic matter and decomposition contribute to soil acidity, soils with little or no growth also encourage alkalinity because of the minimal decomposition activity that happens there.

There are some ways to lower soil pH in alkaline soils and raise it to the soil acidity levels that most plants need:

  • Add acidic materials like sulfur or peat moss to reduce the soil pH.
  • Improve water drainage or prevent water evaporation by adding compost or a mulch of shredded leaves (which are very acidic) to wash away salts and chemicals.
  • Integrate coffee grounds around the plants to make soil acidic.

As always, going with the flow is the best strategy in growing plants successfully in alkaline soils. Grow plants for alkaline soil so that you won’t have to work very hard at improving soil pH:

  • Trees, shrubs and bushes: Butterfly bush, Judas tree, beauty bush, black mulberry, Indian bean tree, yew, rosemary, black maple, northern catalpa, ginkgo biloba, common hackberry, Kentucky coffee tree, Japanese barberry, shore juniper, creeping juniper.
  • Vegetables and herbs: Asparagus, okra, parsley, yams, sweet pea, baby’s breath, beets, cabbage, celery, cauliflower.
  • Flowers: Evening primrose, hellebore, flax, pink carnation, red valerian, yarrow, common lilac, delphinium, clematis, Madonna lily, purple coneflower, phlox, and candytuft.

So there you have it, the lowdown on soil pH and the ways to adjust alkaline soil and acidic soil for successful, high yield growing and gardening. Next up, I’ll introduce you to a great gardening friend of mine called Mycorrhizae, someone you can’t live without if you’re seriously into growing stuff.

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2 Responses to Soil pH – Guide to Acidic Soil and Alkaline Soil Adjustment

  1. Geri Laufer says:

    I believe you may have added the word “lime” by mistake when listing the bullet points on how to lower the pH of alkaline soils and make them more acid.
    Thanks for a great article.

    • Administrator says:

      Thank you for catching that Geri! We have corrected and updated the article. You just earned a free product! I will contact you by email.