Chalk Soil

How to tell if you have chalky soil

Chalk soil can, at first, be quite hard to identify because, depending on the size of the chalk or limestone particles making the soil up, it can be light like sandy soil or heavy like clay.

ploughed field with chalky soil

A field of chalky soil.  If you look closely you can see white stones.
These are chalk and can often be used to write or draw with

Often, but not always, you will be able to see quite a few chalk stones in the soil which can be a giveaway. To be sure, if you put a small amount of the soil into a glass jar or similar container and add vinegar, the alkaline chalk soil will react with the acidity making the vinegar froth up.

Advantages of chalky soil

Chalky soil is very often free draining and, more often than not, is light and therefore easy to dig, cultivate and work with in general.

For the heavier chalk soils, this is not the case as these resemble clay in structure, but heavy chalk soils will be workable much sooner after rain than clay.

All chalky soils will warm up easily in spring and are often prized by farmers.

Disadvantages of chalky soil

The alkalinity in chalky soils can lock up iron and manganese away from plants. This will mean plants in chalky soils may be slow growing or have a yellowish tinge to their leaves.

The soil is usually quite shallow preventing some plants from fully establishing their roots before reaching limestone bed rock; as a result of both this and the generally free draining structure, chalky soil is drought prone.

Plants that like chalk soil

Calcifuges, that is plants averse to alkalinity, will of course not do well in chalky soil; this includes rhododendrons as well as most fruit trees.

Many people with chalky soil in their gardens take advantage of the fact that certain plants such as wildflowers can only grow in chalk soil as, elsewhere, they would be outcompeted by other plants which fail to thrive in the shallow, alkaline soils where wildflowers do well. Indeed, Meadowmat is grown on chalk soils.

Chalk loving plants include:

  • Bellflower
  • Clematis
  • Geranium
  • Lavender
  • Delphinium
  • Cranesbill
  • Hydrangea
  • Honeysuckle

How to improve chalk soils

Unfortunately, it is very difficult to reduce the pH of soils, so it is difficult to overcome the problem of alkalinity in any meaningful way for a significant length of time.

Adding additional topsoil and, as always, organic matter can help but will not completely solve the problem.

The best thing one can do to improve the experience of gardening with chalky soils is to choose wisely which plants they want to grow.  

More about different soil types

Know your soil type

Clay soil

The pros and cons of sandy soil

Are you working with loam soil?