Marlene Affeld
Experienced gardeners know: A healthy productive garden is one in which the plants are compatible with the pH of the soil. Not all soils are the same, and it’s important to recognize that many plants, shrubs, grasses, and trees require a specific nutrient balance.
Some soils have a neutral pH, while others can have an acidic or alkaline pH balance. A pH balance of 7 is considered neutral, and most plants grow better in slightly acidic soil, from 5.5 to 7. Some like soil that’s even more acidic. Acid-loving plants include:
- Vegetables: sweet corn, cucumbers, beans, broccoli, turnips, squash, onions
- Fruits: currants, cranberries, blueberries, huckleberries
- Trees: evergreens, beech, willow, oak, dogwood
- Flowering plants: azaleas, rhododendrons, hydrangeas, camellias, daffodils
Plants That Prefer Acidic Soils
The majority of shrubs, vegetables, fruits, and flowers do best in soil with pH ranging from 5.2 to 7.8, while the majority of grasses thrive in soil with an average pH of 5.5 to 6.5.
Acid-Loving Fruits
Homestead-favorite acid-loving fruits include currants, cranberries, blueberries, elderberry, huckleberries, thimbleberries, and gooseberries, all of which perform best in soil with a pH of 4.0 to 5.0.
Acid-Loving Vegetables
Sweet corn and cucumbers also like acidic soil, doing well in soil with a pH of 5.5 to 7.5. Beans, broccoli, turnips and tomatoes, squash, and onions all require fertile, slightly acid soil with a pH of 5.5 to 7.0.
Parsley, potatoes, peppers, sweet potatoes, radishes, and rhubarb are happiest in soil with a pH of 4.5 to 5.5.
Homesteaders who are cultivating a cash crop to sell at the fresh market, find that many of their customer’s favorite “gourmet” vegetables do best in slightly acidic, nutrient-rich soil. Basil, radishes, asparagus, artichokes, endive, eggplant, lettuce, and leeks favor soil with a pH of 6.5 to 7.5.
Acid-Loving Herbs
Staples in many homestead herb gardens such as, garlic chives, horehound, lemongrass, marjoram, oregano, all varieties of thyme, and rosemary thrive in soil with a pH as low as 4.5.
Other garden fruits and vegetables also tolerate soil with a low pH. These include celery, strawberries, castor beans, dandelion, garlic, chili peppers, shallots, and hops.
Acid-Loving Flowers, Trees & Shrubs
Evergreens and many deciduous trees including beech, willow, oak, dogwood, mountain ash, and magnolias also prefer acidic soil.
A few of my favorite ericaceous (acid-loving) plants include azaleas, mountain heather, rhododendrons, hydrangeas, camellias, daffodils, blueberries, and nasturtiums.
When cultivated in acidic soil these hardy plants brighten the garden with verdant greenery and a glorious display of spring and summer color. If soil pH is balanced, blooms will be robust and firm. If they’re lacking nutrient-rich, acidic soil, blooms will be limp and faded, and leaves will yellow.
What Is Soil pH?
Soils reaction, or pH, indicates the alkalinity or acidity of the soil, measured in pH units. The pH scale has a range of 0-14. Here is the breakdown:
- Acidic Soils: pH below 7
- Neutral soils: pH of 7
- Alkaline soils: pH above 7
As an example, lemon is extremely acidic with a pH of 2.5. Human saliva is considered neutral with a pH of 6.3 to 7.3. Salt water is highly alkaline with a pH of 8.2.
Here’s where it gets a bit confusing. You have to keep in mind that a variance in pH by as little as one point reflects a radical shift. Soil with pH 5 is as much as ten times more acidic than soil testing at a pH of 6. To complicate things further, soil with a pH of 5, is up to 100 times more acidic than that of soil testing with a pH of 7.
Across the United States, soil pH levels vary widely. Soil pH can also vary significantly across a sizeable rural homestead or a small urban plot of land. Thousands of years of interactive erosion of native rocks, types of decomposing organic material, climate weathering, terrain, and physical surroundings all contribute to the pH of the soil.
Reasons For Testing Soil pH
Soil pH impacts the solubility of minerals in the soil as well as the availability of nutrients essential for plant growth. Soil with a high acid content is typically identified as “too acidic” or “hot.”
Extremely strong acidic soils, with a pH of 4.0 to 5.0 pH, may contain high concentrations of soluble iron, aluminum, and manganese, all of which can be toxic to some plants.
If your garden plants display symptoms of nutrient deficiency, despite your best efforts in applying organic fertilizer, the problem is likely related to the pH of the soil.
Soils with a low pH (below 5.5) present a low availability of phosphorous, magnesium, and calcium, with high solubility of iron, boron, and aluminum. Soils with a pH level of 7.8 or higher present a wealth of calcium and magnesium. However, soils with a high pH often have inadequate availability of copper, zinc, phosphorus, boron, iron, and manganese.
Consider testing the pH level of your soil before making decisions that are dependent on the pH of the soil. In the spring, begin each gardening season with accurate testing to determine the pH level of your soil.
Knowing the pH level of the soil in all areas of your property allows you to make the best choices for crop rotation, and decide if soil amendment is required to maximize your crop yield.
Tips For Testing For Soil pH
While home soil pH testing kits promising quick results are available for purchase online or at local home and garden stores, experienced homesteaders know that their results are only as accurate as their sampling and testing process. The more stringent the test, the more accurate the results.
To adequately test a large growing spot such as a vineyard, orchard, or cabbage patch, sketch out a grid of the area and take measured samples across the grid. Thoroughly mix these samples in a tub or wheelbarrow.
Take a generous sample of the mix (two quarts or more) and place in a sealable one-gallon plastic heavy-duty storage bag. Label with your name, sample location, and date. Take the sample to your local county extension office, or state university for a thorough soil mineral, nutrient, and pH analysis.
If you decide to do the testing yourself, the most accurate method is to determine soil pH with a pH meter. Relatively inexpensive, reliable, and reusable, a pH meter is the best DIY choice. It has been my experience that the test kits available at most nurseries and garden shops, which use a testing solution and a color chart, are the least reliable.
Organic Methods Of Raising Soil pH
An application of finely ground limestone, also known as liming, is a widely-used method of increasing the pH of the soil. Apply lime in the spring when turning the soil, because reaction time for limestone is enhanced when moisture levels are high and soil temperatures warm.
Amend your soil with regular applications of well-aged organic compost, mature herbivore manures (cow, horse, mule, llama, goat), peat moss, and pine needles.
Wood ash enhances soil pH. Wood ash is a good source of phosphorous, magnesium, aluminum, potassium, as well as an excellent source of calcium. For generations, apple and stone fruit farmers have spread the ashes from wood stoves and fireplaces around the bases of their orchard trees to improve the soil and encourage fruit production. Use only wood ash, not charcoal briquettes, artificial logs, or coal ash.
Dolomite, a naturally occurring rock, is an excellent additive for soil where magnesium and calcium are low. However, it should be used in moderation as constant applications may result in a nutrient imbalance. Dolomite is a blend of one-part magnesium and two-parts calcium or a 2:1 ratio. The ideal soil ratio of calcium and magnesium should be around 5:1.
References
- Soil Quality Information Sheet, USDA Natural Resources Conservation Service
- Soil pH and Plant Nutrients, Alberta Agriculture And Forestry
- pH — Water properties, The USGS Water Science School
- Raising Soil pH, Wisconsin Horticulture
- Shallots, University of California – Master Gardening Program – Shallots
