Alkaline vs. acidic soil: which do you have and how can you balance it?

June 30, 2015

There are pros and cons to both alkaline and acidic soils when gardening. Read on to find out which soil you have, which plants grow best in that soil and the tricks you can use to balance it out.

Alkaline vs. acidic soil: which do you have and how can you balance it?

Alkaline soil

Alkaline soils can occur anywhere, but they are most common in warm, dry climates where low rainfall levels rarely rinse through the soil, thereby dissolving accumulated salts.

Instead, scant soil moisture evaporates away, leaving behind salts and other chemicals.

  • Having limited natural vegetation also contributes to alkaline soil conditions because little natural decomposition occurs.
  • On the plus side, dry alkaline soils host fewer soil-borne diseases than rich, moist soils that have higher overall levels of biological soil activity.

The vinegar test

  • Add a few drops of vinegar to a soil sample.
  • If it fizzes, the soil is quite alkaline.
  • For a more precise reading, pick up a home test kit or have a proper soil test done.

Add acidic materials

  • Reduce alkalinity by adding acidic materials such as peat moss, sulfur or aluminum sulfate to your soil.
  • Sandy soils need less of each additive than heavier clay soils.

Grow plants that like alkaline soil

Instead of struggling to acidify your soil, grow plants that prefer alkaline conditions.

  • Desirable flowers in this category include Madonna lily, purple coneflower, phlox, candytuft and numerous native wildflowers.
  • Shrubs and trees suited to alkaline soil include lilac, juniper and apricot.

Improve drainage

Improving drainage may help reduce alkalinity by allowing water to wash through the soil and carry away alkaline salts.

  • Put plenty of shredded leaves, compost or other organic matter into the bottom of planting holes.

Add coffee

Coffee grounds help reduce alkalinity, too.

  • In addition to those from your kitchen, check to see if you can get a larger supply of grounds from a local coffee shop.

Mulch it up

Blanketing the ground with organic mulch, such as straw or shredded leaves, prevents evaporation of water, reducing the buildup of alkaline salts.

Acidic soil

In environments that would be thick forests if left in their natural state, the soil tends to be acidic.

  • Leaves, pine needles and fallen trees are all acidic materials, which lead to the formation of acidic soil as they decompose.
  • Much of eastern North America has slightly acidic soil, which is especially prevalent in areas with high rainfall because natural leaching by rain contributes to acidic soil conditions.

The baking soda test

  • For a quick and easy soil test, wet a soil sample and add a pinch of baking soda.
  • If the mix fizzes, the soil may be too acidic for most garden plants and vegetables.

Have a proper soil test done to determine the extent of your soil's acidity. Meanwhile, you can go ahead and begin amending it with lime.

Shower plants with baking soda solution

Plants that prefer neutral to slightly alkaline soil often respond to an occasional shower with a mild solution of 15 millilitres baking soda in two litres of water, which helps them take up nutrients in soil that's a little too acidic for them.

  • Try it on clematis, delphinium and dianthus.
  • They'll show their appreciation with fuller, healthier blooms.

Grow plants that like acidic soil

Many garden plants prefer slightly acidic soil, with a pH between six and 6.5, but woodland plants — both native and non-native — thrive when the pH is even lower.

  • Pine, oak, azalea, camellia, gardenia, strawberry and blueberry are among the plants that grow best when the pH is below 6.

Add limestone

  • To lower acidity in garden soil, apply dolomitic limestone in small doses.

Heavy clay requires more lime than light sand.

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