Perennials for chalky soil

Chalky soils have a degree of acidity (pH) greater than 7. They are called basic or alkaline. Below this, the degree of acidity is said to be neutral (6.5 to 7) or acid (pH <6.5).

Light in colour, they may have chalk mixed with stones or flint. You can test for chalky – or alkaline – soil by diluting a sample in white vinegar. The calcium carbonate in chalky soil will fizzle and bubble in reaction to the vinegar.

In the garden, a chalky soil, rich in fine particles can be sticky, compacted and constrictive in winter; and hard, dry and cracked in summer. The overabundance of calcium ions (Ca++) in the soil can block other positive elements and provoke chlorosis which results in a yellowing of leaves: green veins and pale-green to yellow blades. These include iron (Fe2+), manganese (Mn2+) and boron (B3+).

However, one quality of these soils is that they warm up quickly in spring, so if you add organic matter and fertiliser, you can grow a wide range of plants in them provided that:

  1. you wait –without fail – for the soil to drain before working it;
  2. you use of organic mulch and green fertilisers liberally.

If the pH is highly alkaline and if acidifying a soil is not an option for you, then you will only get good results with calcium-loving plants.

Below, you will find a list of perennials suitable for growing in chalky soil.

Source: Chalky Soil (Royal Horticultural Society)

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