What Makes Soil Alkaline?

Acid soil conditions release aluminum causing hydrangeas to turn blue.

Alkaline soil is soil that has a pH of 7.0 or higher. (Not to be confused with alkali, which is soil containing a specific kind of salt.) The pH of soil is important to gardeners, because different types of plants have a different range of pH values that promote good growth.

Have Your Soil Tested

The easiest way to tell the pH of a plot of ground is to have it tested. Take two or three samples from different parts of your planting area. Keep them separate and label them, as your garden or lawn may have different soil types in different areas. You can test them yourself with a soil test kit, take them to your local university extension office, or hire a private testing service.

Observe the Plants

Wild plants have specific pH requirements just as cultivated ones do. If a plot is growing weeds such as chickweed, chickory and coltsfoot, then chances are it is alkaline, according to online reference Primal Weeds. Hydrangeas planted in alkaline soil will be pink. Acid soils released aluminum in the soil, which will then cause hydrangea blooms to turn blue.

Why Does Alkalinity Matter?

Most garden vegetables like soil that has a pH range of 6.5 to 7.5. If the pH of the soil is not correct for the plants they will not grow correctly, may not bloom or produce fruit.

Causes for Alkalinity

Areas of low rainfall with desert-like conditions tend to have a high alkalinity. The presence of high amounts of lime in the soil tends to make it alkaline. Previous cultivation or construction and movement of soil from one place to another can create alkaline conditions.

Lowering Alkalinity

Alkalinity can be lower by adding sulfur, various types of sawdust, pine needles, shredded leaves (particularly oak) or peat moss to the soil. Working in organic matter tends to make either acid or alkaline soil more neutral.

Raising Alkalinity

Add lime or potash to the soil to raise alkalinity. These substances should be added carefully--a little bit goes a long way, according to online gardening reference PlanTea.

References

• Basic Info 4 Organic Fertilizers: Alkaline Soil
• Plantea: Acid or Alkaline?
• Primal Seeds: Wise Weeds