Geography & Geology on the Isle of Wight
The key to the Isle of Wight’s reputation as ‘The Garden Isle’ is hidden within its geological and therefore geographical make up and its unique climate, including a micro climate in the south of the Island.
Also as it is one of the most southerly parts of the UK, the Isle of Wight has a milder sub-climate than most other areas, which makes it a popular holiday destination at it also has a longer growing season than many other areas in southern Britain.
The Island’s unique geological structure gives rise to a very varied collection of landscapes with just about every soil and rock type in the south of England being represented here.
The chalk ‘backbone’ that runs through the Island from West to East gives a swathe of downland, emerging as the high chalk cliffs at Culver to the East and The Needles and Tennyson’s Down to the West.
Another huge chunk of chalk emerges above the south-eastern coast, rising to the highest point on the Island above sea level (241 metres/791 feet) at St Boniface Downs above Bonchurch and Ventnor.
Further round the coast to the west from Ventnor is the Undercliff; an area beneath high greensand cliffs that has a lush Mediterranean micro-climate. The land between the sea and the cliff is the result of a huge rock fall thousands of years ago, but because these rocks sit on blue slipper clay the land is still ‘on the move’.
Facing South West, the cliff behind this area tends to protect it from colder winds from the North and East that pass over it and out to sea.
“Because it is south facing it has all the hours of daylight and the ameliorating effect of the sea helps to keep it warmer” explained Chris Kidd, Head Gardener at Ventnor Botanic Gardens in the Undercliff at St Lawrence.
“The land here is made up from rocks you also get a radiator effect because the rocks are a pale colour and they reflect the light. Also light levels are higher here because we don’t have the sea mist problem that Cornwall has,” he added. “The quality and quantity of light here is better.
“We’re famous for the Echium Pininana that our curator Simon Goodenough introduced in 1986,” said Chris. “It is native to Grand Canaria where it is found at high altitude up the volcano. It likes the alkaline conditions here,” he added.
The Botanic Garden has become renowned worldwide for the collections of plants that grow in its Mediterranean type of climate. Gardeners from the area, and indeed other parts of the Island, have attempted to grow them in their own gardens with a degree of success.
The chalk running through the Island has a alkaline effect upon the resulting soils and gardeners on the Island tend to find that if they live near it or to the south of it then they have alkaline conditions.
To the north of the chalk ridge the rock types are predominantly clays and a little limestone, and here the soil conditions can be more acidic or ericaceous.
Because of the nature of the Island’s geology, gardeners are often advised to take a soil test from their land before embarking on planting. Those with larger tracts of land can even find that they have both acidic and alkaline conditions.
The River Medina divides the Island neatly in half and cuts through the chalk ridge and two more rivers cut the ridge, both called The Yar. The Western Yar flows from Freshwater to Yarmouth and the Eastern Yar flows from Yaverland to Bembridge Harbour and both almost dissect the Island – Bembridge was once an island in its own right.
Obviously the river valleys are fertile areas with rich cattle grazed pastures and arable fields, with estuarine mudflats towards their mouths in the Solent that are a haven for birds.
The Island also has more miles of coastline where the trees grow right to the water’s edge than anywhere else in the South of England.