In the realm of gardening and landscaping, grasping the nuances of soil pH proves indispensable for fostering robust plant life. Within the United Kingdom, soil pH levels exhibit notable diversity, exerting profound effects on the growth and vitality of vegetation. Through this insightful blog, we embark on an exploration of soil pH's definition, its impact on plant well-being, and the selection of trees thriving amidst varying soil conditions across the UK.
Understanding Soil pH:
Soil pH serves as a gauge of the soil's acidity or alkalinity, measured on a scale ranging from 0 to 14, with 7 denoting neutrality. Values below 7 signify acidic soil, while those exceeding 7 indicate alkaline soil. This pivotal metric plays a crucial role in plant cultivation, influencing nutrient accessibility and microbial activity, both pivotal for sustaining optimal plant health and growth.
Soil pH in the UK:
In the United Kingdom, soil pH levels exhibit variability influenced by geographical location and underlying geological formations. Typically, areas with limestone or chalk bedrock tend towards alkaline soils, whereas regions characterised by granite or sandstone bedrock often harbour acidic soils. Nevertheless, local nuances abound, with soil pH also subject to modification by factors such as precipitation patterns, vegetation cover, and human activities.
It is reassuring to note that the majority of soils in the UK tend towards neutrality, boasting a pH of 7 or slightly lower. These soils present a spectrum of textures, ranging from heavy clays to sandy loams, enabling a broad range of plant growth with minimal issues.
Acid soils are more widespread than alkaline soils, and can be found making up large areas of heathland and coniferous woodland, such as Dartmoor National Park, York Moors, Yorkshire Dales, Brecon Beacons, and the Cairngorms. Conversely, alkaline soils are predominantly found in areas characterised by chalky terrain, notable examples being the North and South Downs, Yorkshire Wolds, Salisbury Plain, and Chiltern Hills.
Choosing Trees for Different Soil Types:
Over time, certain plant species have evolved to thrive in specific soil environments, confining their growth to particular locations while bestowing upon them a competitive edge. For example, ericaceous or calcifuge plants have adapted to flourish in acidic soils, exhibiting limited growth potential in alkaline environments. On the other hand, calcioles are plants adept at thriving in alkaline or lime-rich soils but struggle to prosper in acidic conditions.
1. Acidic Soils (pH below 7):
Rhododendron (Rhododendron spp.): Renowned for their vibrant blooms, rhododendrons flourish in well-drained acidic soils.
Blueberry (Vaccinium spp.): Ideal for acidic soils, blueberries require acidic conditions to produce abundant fruit
Scots Pine (Pinus sylvestris): A native pine tree that thrives in acidic soils, Scots Pine is known for its tall stature and distinctive orange-brown bark.
Silver Birch (Betula pendula): A hardy, versatile and elegant tree, Silver Birch is well-suited to acidic soils and is prized for its delicate foliage and silver-white bark. Commonly found across the UK.
2. Neutral to Neutral to Slightly Acidic Soils (pH around 7):
Rowan (Sorbus aucuparia): Also known as mountain ash, rowan trees exhibit resilience across various soil conditions, including neutral to slightly acidic soils. Admired for their vibrant red berries, they serve as a magnet for wildlife, attracting birds and other creatures.
Hawthorn (Crataegus spp.): With its dense foliage and vivid berries, hawthorn thrives in neutral soil environments, flourishing along hedgerows and woodland edges to create picturesque landscapes.
Common Oak (Quercus robur): A symbol of strength and longevity, common oak trees can adapt to various soil types, including neutral soils, and are iconic features of the UK landscape.
European Beech (Fagus sylvatica): With its glossy foliage and smooth grey bark, this is a majestic tree. European Beech thrives in neutral to slightly acidic soils and adds a touch of elegance to woodlands and parks. It also does well in slightly alkaline soils.
Field Maple (Acer campestre): A native maple species, Field Maple grows well in neutral soils and features attractive lobed leaves that turn vibrant shades of yellow and orange in autumn.
3. Alkaline Soils (pH above 7):
Yew (Taxus baccata): Renowned for its dark foliage and tolerance to alkaline soils, yew trees are often found in churchyards and formal gardens.
Sweet Chestnut (Castanea sativa): Preferring well-drained alkaline soils, sweet chestnuts thrive in warmer regions of the UK and produce delicious nuts in the autumn.
Common Hornbeam (Carpinus betulus): Known for its dense canopy and distinctive fluted bark, Common Hornbeam is well-suited to alkaline soils and is commonly used for hedging and screening.
Holm Oak (Quercus ilex): A Mediterranean species that thrives in alkaline soils, Holm Oak features evergreen foliage and can withstand coastal conditions.
White Willow (Salix alba): White Willow adapts well to alkaline soils and is recognised for its slender leaves and graceful form. It is often found near water bodies due to its affinity for moist soil conditions.
How to tell if a plant is struggling:
The signs that a plant is not suited to the pH of the soil it's growing in include chlorosis (yellowing of the leaves), stunted growth, and curling leaves. This is because the availability of nutrients varies in soils according to their pH.
For example, in acidic soils, iron levels tend to be relatively high, whereas in alkaline soils, they are lower. Furthermore, alkaline soils typically exhibit a higher concentration of calcium compared to acidic soils.
Determining your soil's pH is a straightforward task. All you need is a soil pH test kit, readily available in the market at an affordable price.
Alternatively, you can assess the soil pH by observing the plant species thriving in your garden and its surroundings. Indicators of acidic soil include rhododendrons, camellias, heathers, magnolias, and conifers like Scots pine and larch. Conversely, the presence of honeysuckle, lilac, clematis, and lavender suggests alkaline soil conditions.
Adjusting Soil pH:
You have the flexibility to cultivate both acid-loving and alkaline-loving plants, even if your soil isn't initially suitable. Container gardening offers a versatile solution, allowing you to grow a wide variety of plants, including shrubs and trees, while maintaining control over soil conditions. Consider utilising raised beds and containers filled with ericaceous compost to create and sustain acidic environments through applications of sulphur or ferrous sulphate. Although, for acidic soils, raising pH levels can be achieved by adding lime, although this should be done cautiously to prevent excessive alkalisation. It's generally simpler to raise soil pH to make it more alkaline than to lower it.
To Acidify Soil (for alkaline soils): Incorporate elemental sulphur, organic mulches, or acidic fertilisers to lower soil pH and create acidic conditions.
To Alkalise Soil (for acidic soils): Apply lime or wood ash cautiously to elevate soil pH, ensuring careful monitoring to prevent over-alkalisation.
Understanding soil pH is paramount in selecting trees that will thrive in your garden or landscape. By opting for trees suited to your soil type and implementing appropriate soil pH adjustments, you can cultivate lush, healthy landscapes tailored to your local soil conditions.
Regardless of your soil composition, you have the opportunity to craft vibrant outdoor spaces that enhance biodiversity and contribute to the aesthetic beauty of the UK's diverse landscapes.
Whether faced with acidic, neutral, or alkaline soils, a plethora of tree species awaits your selection, ensuring that your green spaces flourish for years to come.