Soil Types , Soils are aggregates or complex mixtures of minerals, water, air, organic matter, and countless organisms. Soils supply plants with nutrients, most of which are held in place by particles of clay and organic matter (colloids) soil types.
The nutrients may be adsorbed on clay mineral surfaces, bound within clay minerals (absorbed), or bound within organic compounds as part of the living organisms or dead soil organic matter.
Chalky soils are generally very alkaline and often called basic soils. Such soils are free draining, able to hold water but only a little and easily dry out. Chalky soils are made of particles from solid but soft and easy-to-break down rocks.
Chalky, alkaline soils are common in Britain and many of the country’s most productive agricultural areas are based on chalky soil. But while they’re usually fertile, plants can find it hard to take advantage of the nutrient content because of chalky soil’s high alkalinity – stopping plant roots from absorbing iron. Moreover, it’s shallow and stony while the organic matter added to chalky soil can easily decompose, making it very challenging to garden.
It’s common for plants on chalky soil to suffer from poor growth and chlorosis (or yellowing of leaves) since they cannot absorb manganese, iron, and other minerals through the roots.
The challenges brought by gardening in high-alkaline, chalky soils could overwhelm a home gardener – and crossing out other plants in your garden (even if they’re a favourite) and sticking to ones that easily grow in alkaline conditions is usually the most practical option.
Chalky soils have a layer of chalk or limestone bedrock beneath the surface, hence the name.
These soils however can differ greatly from each other despite being in the same category:
Some chalky soils can have a light and peaty top soil, others have a lot of gravel, and there are chalky soils rich in clay content. It’s not surprising that properties of certain chalky soils depend on other components or particles present in the ground.
Soils rich in chalk are common in the south-east region of England. These soils are usually very shallow, have full clumps of white chalk, and can contain flint which often proves annoying when cultivating or digging the ground.
The chalkiest of chalky soils are usually stony and contain hard-to-penetrate regions coupled with large, sharp flints, giving plant roots trouble expanding as they often bump into these hard lumps.
It drains too easily and is unable to hold on to water for plants. This can be a problem especially during the summer season. People who garden on chalky soil must be prepared to water and feed their garden with greater frequency than what’s necessary in other types of soil (E.g. clay and silty).
Chalk-rich soils often have a pH of 7.5 or more, making them alkaline, a problem for most plants and gardens as it means minerals like manganese and iron are unavailable.
This stifles the growth and yellows the leaves of many plants – and one should regularly fertilise the ground to avoid these problems.
These soils can have a clay-like feel and appearance as mentioned – but be careful as the clay-like element might be fine calcium carbonate which makes the soil poor for planting. If the particles are indeed clay, that’s good news as these fine bits are known for holding onto water and nutrients very well, counteracting the chalky soil’s free draining properties.
There are several ways to find out and determine if you have chalky soil in your garden. You can perform a vinegar test by placing a handful of your soil in a jar of vinegar. If the soil froths, it means it has chalk content and is rich in lime.
Alternatively, you can add a handful of soil to a glass jar and fill it with water. Stir it well and let the particles settle for two hours, then check out the glass jar. Chalky soil will leave the water greyish in colour and will have a white, gritty layer of chalk fragments at the jar’s bottom.
PREPARATION (soil types)
Chalk soils share many similarities to sandy soils – poor water and nutrient-retention properties being examples. Those that only have a thin layer of soil to cover the chalk beneath are likely to suffer from lack of moisture as the water easily flows through the chalk and out of reach for the roots.
The high alkalinity of the soil is also an additional problem – taking roses, hydrangeas, and other ericaceous plants out of the question as these plants require iron and manganese for proper, healthy growth. The mentioned plants often suffer from dwarfing and chlorosis when grown in chalky soil.
It’s clear that successfully gardening on chalky soils – especially those that have thin layers of soil covering solid chalk – need a lot of work and preparation. Adding a lot of organic matter to the ground is a must and should be done regularly. Organic matter decomposes faster in chalky soil due to its properties – and going overboard on adding organic matter is near-impossible.
It’s recommended that you dig as deeply as possible into the ground each year, allowing you to really knead or mix the organic matter into the soil. It takes years of regularly carrying out the above steps to achieve results, but doing so will increase the depth of soil that’s suitable for gardening. Don’t forget that the topsoil of a chalky garden site needs some loving too so add organic matter to the topsoil as well and mixing it in for good measure.
Just about any organic matter will do for chalky soils as it will help keep it fertilised.
There are gardeners, however, that recommend peat, leaf moulds, and other acidic materials to counteract the soil’s alkalinity – only slightly though.
You need all the help you can get when gardening with chalk-rich soil so keep this in mind too. Don’t forget to apply fertiliser to your chalky, garden soil before you plant during spring for good measure.
READ MORE: All You Need To Know About Sandy Soil
It is possible to reduce chalky soil’s alkalinity by adding sulphur into the ground, but this isn’t recommended for home gardeners. Large applications are necessary to counter the free calcium carbonate content (0.5-1kg of sulphur per meter squared) and applications are necessary over many years.
You also need to be choosy when gardening on chalky soil as many plants don’t thrive in it. Roses, azaleas, rhododendrons, and camellias are to be steered clear from since planting them on chalk-rich soil may only frustrate you. You also want to pick plants that tolerate not just the soil’s high alkalinity but also its shallow depth and poor water-retention properties.
We’ll take a look at some of the suitable plants for chalky soil in a later section.
PROS AND CONS
What’s Nice About Chalky Soil
You may get the impression that gardening in chalky soil is almost doomed to failure after reading its characteristics above.
But remember: some of Britain’s most successful and productive agricultural regions are based on chalky soil. It’s a challenging soil to garden, but it can be done with the right preparation. Chalky soils can be moderately fertile and provide ideal growing conditions for a wide variety of plants as long as you regularly apply organic matter and fertiliser.
Not to mention you don’t have to worry about floods in chalky soils: they’re usually elevated and are very porous like sandy soil so flooding is very rare. The same sand-like properties of chalky soil makes it easier to warm especially during spring. This allows gardeners to start seeding and sowing at an earlier date.
What’s Not-So-Nice About Chalky Soil
Chalky soils are generally full of hard, sharp flints and stones, which makes digging the ground challenging. It’s shallow and light – and depending on the plants you pick, it may not provide ideal growing conditions. It’s advisable that you go for plants that can thrive in well-drained soils.
READ MORE: All You Need To Know About Peaty Soil
The poor water and nutrient-retention means chalky soil can be extremely dry during summer, requiring frequent watering to keep the ground moist. That, combined with its high alkalinity, makes chalky soil nutrient-poor since plant roots are unable to absorb the locked-up iron and manganese.
This bushy and deciduous tree dons leaves that are usually 10cm in width and have a heart-shaped appearance. The tree loves well-drained soil and can thrive both under the sun or partial shade. Its flowers are rosy-pink in colour, shaped like peas, and are often found in clusters. The fruit of the Judas tree has a noticeably flattened pod-like appearance and purplish colour.
This deciduous tree is massive and robust – donning a broad and spreading crown, dainty flowers, and rough fruits. Its leaves are elliptic in shape, yellow-green in colour during spring but are rich brown in winter. It grows easily in well-drained soil and would appreciate the free-draining properties of chalky soil.
READ MORE: All You Need To Know About Loamy Soil
Chalky soil is rich in lime content, but as long as the green is deep and fertile the lime-tolerant common oak doesn’t mind. It’s a large tree that grows a broad, impressive crown. Its leaves have shallow and rounded robes that turn reddish brown during the winter season.
READ MORE: All You Need To Know About Clay Soil
This is an evergreen shrub that thrives in well-drained soils and is flexible enough to grow both in sun or partial shade. It’s commonly grown in flower borders, courtyards and informal gardens, and other places because of its ornamental value. Its leaves are broad – green in colour but are bordered by bright yellow (pink during winter) margins.
NORWAY MAPLE (soil types)
Not only does it grow well in chalky, free-draining soils, the Norway maple is also shade and pollution-tolerant – precisely the reason why it’s commonly grown in parks and gardens in the UK since the 17th century. The Norway maple can grow male and female flowers on the same or separate trees. Its female flowers develop into samaras or winged seeds once pollinated.
The ragwort is a fast growing shrub that’s very tough against severe and extended frosts. It’s a popular shrub in gardens that can grow up to 2 meters. Its new shoots grow rapidly with sudden changes in its direction, giving the ragwort a very roundabout appearance when surveyed beyond the leaves and flowers.