In Britain, there are many alkaline soils, many of which are chalky because they are made from chalk or limestone. Even though they have the best agricultural soils in Britain, gardening can be difficult there. Chalky soils are typically shallow, stony, and free-draining. Adding organic matter can quickly decompose, making it hard to keep fertile. Chlorosis, or yellowing of the leaves, is caused by the plants’ inability to absorb iron and manganese through their roots. The best course of action is to select plants that thrive in alkaline environments.
- Chalky soils have a pH of 7.1 or above
- Calcicoles are plants that love lime and can live in soil with a lot of lime, like Syringa.
- Calcifuges are plants that can’t grow normally in soil that has a lot of lime (they hate lime), like Rhododendron.
- Smaller plants establish themselves more quickly than mature ones.
- Chalky soils are ideal for prairie and Mediterranean plants.
Identifying Chalky Soils
Chalky soils have a wide range of characteristics, from gravelly to clay-like. It’s possible that the clay-like substance is mostly calcium carbonate, which is terrible for plant growth. However, true clay may have a greater capacity for water retention and higher nutrient levels in the soil.
Chalky soils are distinguished by:
- Soils that are chalky or have a lot of lime in them can be light or heavy, but they are mostly made of calcium carbonate and have a very alkaline pH (7.1-8.0).
- If soil in a vinegar jar froths, it contains free calcium carbonate, also known as chalk or limestone, and is high in lime.
- Soils that are very chalky may have large, easily split flints and visible lumps of chalky, white stones. Limestone lumps can be found in limestone soils.
Gardening With Chalky Soils
Naturally, chalk and limestone are abundant in lime-rich soils, which are frequently associated with herb-rich pastures in the Downland and chalk and limestone woodlands.
Because manganese and iron can be “locked up” in the soil, making them unavailable to plants, light chalky soils frequently contain a lot of stones, can be extremely dry in the summer, and frequently lack nutrients. They are also shallow and light, but their weight and looser construction make them easier to cultivate than “heavy” clay.
However, due to their elevation and porosity, light alkaline soils rarely experience flooding. They also warm up quickly in the spring, can be moderately fertile with good manure and fertiliser, and are ideal for growing a wide range of plants.
How To Improve Chalky Soils
- Dig in a lot of organic matter to help the soil retain moisture and have more humus (which can break down and disappear quickly).
- Most of the time, chalk and limestone subsoils have deep cracks where tree and shrub roots can easily find moisture. However, in some cases, you may need to break up the subsoil to get enough depth to plant woody plants.
- Apply fertilisers
- To keep the soil moist, add organic matter to the mulch.
- Crimson clover, vetch, and bitter blue lupin are examples of green manure that can be grown to help the vegetable garden fix nitrogen before planting elsewhere.
Note: Because it would take a significant amount of sulphur over a long period of time to counteract the free calcium carbonate, it is impractical to add sulphur to chalky soils in order to lower their alkalinity.
Lowering the pH of the soil—which lowers alkalinity—is more challenging than raising the pH—which raises alkalinity. As a result, pH reduction is only useful in soils that are slightly alkaline. Every time an effort is made to lower alkalinity, the soil should be tested annually to observe any changes in pH and, if necessary, the treatment should be repeated.
Applying sequestered iron in a liquid form that also contains manganese and magnesium can partially remedy lime-induced chlorosis, which is characterised by yellowing of the veins. However, if it becomes clear that this is necessary on an annual basis, serious consideration should be given to either growing the affected plant in a container filled with compost that does not contain lime (ericaceous) or replacing it with plants that are suited to chalky soils.
Importing topsoil may be necessary to increase the growing depth on very shallow chalk soils (less than 10 cm/4 in). The topsoil depth for lawns should be at least 10-15 cm (4-6 inches); for borders of 20 to 30 centimetres and for shrub beds larger than 45 centimetres (18 inches).
Top 10 AGM Plants For Chalky Soils
- Clematis e.g.: clematis ‘Mayleen’
- Dianthus e.g.: dianthus ‘Candy Floss’
- Geranium e.g.: Geranium Rozanne – ‘Jolly Bee’
- Lavandula e.g.: Lavandula angustifolia ‘Munstead’
- Fuchsia e.g.: Fuchsia Dollar Princess
- Pyracanthas e.g.: Pyracantha Orange Glow
- Agapanthus e.g.: Agapanthus Fireworks
- Helleborus e.g.: Helleborus argutifolius
- Hosta e.g.:Hosta Night Before Christmas
- Viola e.g.:Viola Molly Sanderson
Frequently Asked Questions
“Chalky soils are best for plants that don’t need a lot of nutrients and like to have good drainage,” says Chris Bonnett, a gardening expert for The Express.