We are frequently asked to design gardens on chalk. Some plants we know will thrive, some will go yellow and fade away. I thought it would be interesting to find out why the chalk hills around us formed and look into some of their unique properties.
Spanning a picturesque 100 miles between Winchester and Eastbourne, the South Downs are a beloved gem in the English countryside. Granted national park status in 2010, these rolling hills attract an impressive 46.3 million visitors each year. The chalk downlands have been sculpted over centuries by both nature and the generations of communities that have called this area home.
The South Downs boast a fascinating geological history that spans millions of years. Between 100 and 112 million years ago, layers of clay, mudstone, and siltstone settled across southeastern England, forming what’s known as the Gault Clay Formation. Fast forward to around 65 to 100 million years ago, in the Cretaceous period, when the area was submerged under tropical seas. This is when the iconic chalk deposits, now synonymous with the South Downs, were laid down.
These marine deposits settled atop the older layers and, over time, were uplifted and folded into a large dome called an anticline. As time passed by, weathering and erosion sculpted this dome into the rolling hills and valleys we admire today.
Chalk, being porous, acts like a giant sponge, storing vast amounts of water. This natural reservoir is a vital resource, supplying fresh drinking water to over 1.2 million people in and around the South Downs. And it’s this characteristic of the chalk which has created some of the recognisable features seen within the downs.
But let’s rewind to around 20,000 years ago during the last ice age. With winter temperatures averaging between 0 and 4°C, the water in the chalk froze, creating a hard, impermeable surface called permafrost. This allowed water to flow over the surface, carving out valleys as it went. Notable examples include Devil’s Dyke and the South Downs escarpment. They are called dry valleys as they don’t house rivers, but were shaped by the ice age into the striking features we see today.
People have called the South Downs home for centuries, and their presence has transformed this landscape into the beautiful, albeit unnatural, habitat we see today. The story begins in the Neolithic era, when settlers first arrived, and farmers began clearing the woodlands. As time went on, the soil’s fertility faded and erosion took its toll on the slopes, prompting farmers to move on. As they travelled across the downs, they cleared more land and left behind grazing animals on the infertile land.
And today, farming still dominates the South Downs, with 85% of the area dedicated to agriculture. This shift from traditional grazing to more intensive farming practices accelerated around the time of World War II, marking a significant change in the landscape’s use and appearance.
The chalk grasslands of the South Downs are a treasure trove of biodiversity, with up to 45 species thriving in every square metre. Among these are beloved favourites like the Adonis blue butterfly, skylarks, and the round-headed rampion. These grasslands are essential for many rare and specialised species that depend on the unique environment they provide.
Take the wildflower population, for instance. These vibrant blooms support over 30 species of butterflies during the summer months. The Adonis blue butterfly, in particular, is a chalk grassland specialist, feeding exclusively on horseshoe vetch. However, the decline in grazing of the landscape has allowed coarse scrub to encroach upon these grasslands, diminishing the biodiversity. This encroachment threatens the wildflowers and, consequently, the many species that rely on them.
Gardening on chalk:
Gardening on chalky soil can be a bit of a challenge due to its tendency to drain quickly, making it prone to drying out. In gardens with a chalk base, you’ll often find the soil is alkaline, quite shallow—sometimes just a few inches deep—and occasionally rocky with chunks of flint and chalk.
Because chalk is so porous, water and nutrients easily drain away, leaving the soil low in fertility. These factors can make it tougher to maintain a lush, healthy garden. Although with some adjustments and a few strategic approaches, you can still cultivate a thriving garden on chalky ground.
Breaking up the ground and chalk to a depth of about 75cm is a fantastic way to help plants take root and spread out more easily. To give your soil a boost, mix in plenty of organic matter like compost or well-rotted manure. This improves the soil structure and adds extra nutrients.
Mulching is another great tip—it helps retain moisture, especially during dry summer months, and it also suppresses weeds that compete for the limited nutrients in the soil.
A method to deepen you topsoil layers is lasagne gardening technique. Start by covering the area with a thick layer of cardboard or newspaper and soaking it with water. Then, add a 2–3-inch layer of brown materials like straw or leaves, followed by a 1–2-inch layer of green materials like grass clippings. Keep alternating these brown and green layers, watering each one, until you reach a height of 18-24 inches. Finish with a final layer of topsoil, and you’ll be ready to plant!
There are many different types of plants the grow well in chalky gardens. Its also suggested to plant smaller plants due to the ground conditions so they can establish quicker.
English lavender (Lavandula angustifolia) is a classic choice for chalky soil as it thrives in well drained, alkaline soils. It adds a beautiful purple blossom to any garden whether in a boarder or herb bed.
Dianthus is a resistant perennial that flowers in the summer months and has delicate pink flowers and slender stems adding elegance to the garden.
Mediterranean Strawberry tree (Arbutus uendo) is an evergreen shrubby tree that grows to around 8m tall with white flowers in the autumn time. It should be position in the full sun but should be sheltered from cold drying winds.
Although a chalk garden may be difficult to start off with there’s such a range of beautiful plants that will thrive in these conditions and creating striking designs.
August:
Obviously keep up the watering in this sustained hot weather, especially with plants in pots and new plants.
Top up the mulch to retain moisture and keep weeds down
Keep pinching out your tomatoes and sowing new rills of lettuce, radishes and spinach
Time to prune the bigger shrubs that have just finished flowering like Wygelia, Philadelphus, and Spirea- cut out the old flowering wood back to new growth that next year’s flowers will bloom from them
Mow your lawn on a higher setting now to keep moisture in the grass to help mitigate against summer browning in dry spells
Have a bit of a rest- things slow down in the garden now, and so can you.
Where to go in August
Visit the Hanna Pechar Sculpture gardens of course!
Booking from Tuesday to Sunday
Black & White Cottage
Standon Lane
Ockley
Dorking
Surrey
RH5 5QR (postal only – use RH5 5QU for SatNav)
UK
Telephone: (+44) (0) 1306 627 269
