Soil pH Explained

Even though we may not usually give it much attention, “soil pH” is a word combination we see on growing medium packaging, in soil requirements for nearly each plant, and in care guides online.

In this insight, we explain what it is, the types there are, which plants prefer a certain kind, how to test pH, as well as how to alter it if necessary.

What Does pH Stand For?

Historically representing the word combination “potential (of) Hydrogen”, soil pH shows how many hydrogen ions there are in it.

What’s in the Numbers?

A scale from 0 to 14 marks 3 basic categories of pH content in the soil, where

  • <7 is acidic,
  • 7 is neutral,
  • and >7 is alkaline.

But the soil pH scale according to the USDA is as follows:

  • Extremely acidic—3.5–4.4
  • Slightly acidic—6.1–6.5
  • Neutral—6.6–7.3
  • Slightly alkaline—7.4–7.8
  • Extremely alkaline—above 9.0

Is This Measurement Always the Same?

It isn’t. The pH fluctuates depending on the microorganisms present in soil, moisture levels, seasons, temperature, and other factors.

Why Do I Need to Be Mindful of It?

Most of the time, the health of your greenery depends on it. For instance, unless the soil has a required pH, some plants can’t absorb the necessary nutrients from it. It also plays a significant role in pesticide effectiveness.

A value from 6 to 7 (with 6.5 as the optimum) is mostly universally acceptable, but some plants might need pH below or above this measure. Further, we’ve compiled lists of plants based on the kind of soil pH they enjoy most.

Those That Prefer Acidic Mediums

  • Flowering dogwood (Cornus florida)
  • Gardenia (Gardenia jasminoides)
  • Heather (Calluna vulgaris)
  • Northern highbush blueberry and lowbush blueberry (Vaccinium corymbosum and Vaccinium stenophyllum)
  • Rhododendron plants

Neutral Dwellers

  • Bluebeard (Caryopteris x clandonensis)
  • Bower plant (Pandorea jasminoides)
  • Gerbera daisy (Gerbera Ă— hybrida)
  • Mandarin orange (Citrus reticulata)
  • Moreton Bay fig (Ficus macrophylla)
  • Purple coneflower (Echinacea purpurea)

Those That Thrive in Alkaline Conditions

  • Burningbush (Bassia scoparia)
  • English lavender (Lavandula angustifolia)
  • Russian sage (Salvia yangii)
  • Shield aralia (Polyscias scutellaria)
  • Shore juniper (Juniperus conferta)
  • Thyme (Thymus)

What Flowers Change Colors Depending on pH?

The bigleaf hydrangea (Hydrangea macrophylla) flowers are blue in highly acidic mediums (preferably 5.0–5.5) and pink in slightly acidic ones (ideally 6.5–7).

No other plants whose flowers are consistently affected like that have been discovered yet.

How Do I Test Soil pH?

There are a bunch of ways to do that.

  • The most common practice is using pocket pH meters that need regular calibration with fresh reagents. If you clean their sensors between uses, they’ll serve you for a long time.
  • Soil test kits are available in specialized stores, too (and some of them let you assess nutrient content as well). Be sure to store them according to label instructions and acknowledge their best before date.
  • Sending a sample to the nearest lab is also worth considering.
  • However, if you’re up for getting your hands dirty and a rough assessment between acidity and alkalinity is enough for you, you can carry out a home test. Using a trowel, scoop some soil from the necessary area into a plastic container. The equipment should be clean. Add some vinegar to the soil so that the proportion is 1:1. A fizzy reaction indicates alkalinity; the more prominent it is, the higher the pH is. Repeat the same process with a fresh set of tools and a new scoop of soil, but this time, use water instead of vinegar. After that, add baking soda in equal proportion. A reaction will indicate soil acidity. The more conspicuous it is, the lower the pH is.

Mind you, the soil content may be different depending on which part of your garden you take it from.

As for when you should test it, do it every few years or before planting a pH-fussy plant.

How Can I Influence It?

In fall, you can use pine needles, aluminum sulfate, acidic peat, ammonium sulfate, or sulfur to acidify soil. To alkalize it, add fine limestone or wood ashes. A laboratory test will let you know how much you’ll need to amend the soil. Otherwise, you can start small and test the result after each amendment until you’re satisfied with it.

In any case, you’ll need more than one amendment to make lasting changes to soil pH.

Now you know what pH is and why it matters, understand the numerical values describing it, and can test and amend the soil pH in your pots, beds, and lawns. More aware of its significance, you can take your plant care skills to the next level.

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