Your guide to understanding your garden's soil pH (and helping your plants thrive)

Understanding your garden's soil pH level—and even learning how to adjust it—is key to helping your plants take up nutrients and thrive.

In very alkaline or acidic soil many plants have trouble taking up nutrients, so they fail to thrive.

• Fortunately, the vast majority of garden plants are somewhat adaptable, growing nicely when the pH is between 5.5 and 7.0, and it's not difficult to alter any soil's pH by at least a point.

Two of the major chemical characteristics of any soil are its acidity and alkalinity, which are measured on the pH scale.

• The pH scale runs from zero (pure acid) to 14 (pure alkaline); its neutral point is seven.
• Soil pH never runs toward the scale's extremes, but small numerical differences have big implications for plant growth.
• In very alkaline or acidic soil many plants have trouble taking up nutrients, so they fail to thrive. Fortunately, the vast majority of garden plants are somewhat adaptable, growing nicely when the pH is between 5.5 and 7.0, and it's not difficult to alter any soil's pH by at least a point.

Have a soil test done or use a soil test kit from a garden centre.

1. The procedure is simple: crumble 15 millilitres (one tablespoon) of soil taken from a depth of 10 centimetres (four inches), add a measured amount of distilled water, stir and let it settle.
2. A short time later, you can dip litmus paper into the water and match its colour to a guide sheet that comes with the kit.
3. Sending off for a detailed soil analysis is always a smart move, but learning to do your own pH tests has advantages, too.
4. You can more easily track changes, and it's the best way to get to know differences in the soil in different parts of your yard.

Lime and sulfur are the two main tools gardeners can use to lower or raise the soil's pH.

• Additionally, adding organic matter and using mulches can help stabilize the soil's pH.
• Once you understand your soil's natural pH tendencies, you can fine-tune your gardening practices to prevent radical spikes or dips in pH levels.

Use this guide as a starting point for adjusting the pH of nine square metres (100 square feet) of average soil by one unit on the pH scale.

Soils that are rich in organic matter or dense by nature usually need more lime or sulfur than porous, nutrient-poor soils.

Clay soil

•  To raise 1 point:  3.6 kg (8 lb) lime
• To lower 1 point: 3 kg (6.5 lb) garden sulfur

Sandy soil

• To raise 1 point: 1.4 to 1.8 kg (3 to 4 lb) lime
• To lower 1 point: 1.1 kg (2.5 lb) garden sulfur

Fertile loam

• To raise 1 point: 2.7 kg (6 lb) lime
• To lower 1 point: 2.5 kg (5.5 lb) garden sulfur